NBEO Part 1

A 32-year old female is seen at your office complaining of a recent onset of blurred vision, only at a distance. A thorough case history reveals that she recently began taking a new medication which you correctly assume has induced myopia. Which of the following medications is MOST likely to be the culprit?

Isotretinoin, birth control pills, and diuretics, among many other drugs, can cause myopia in some patients. Myopia mostly likely results from corneal swelling, which steepens the curvature of the cornea. Drugs that cause swelling of the lens, accommodative spasm, or edema of the ciliary body will also result in myopia. A reduction in the dose of the medication or cessation of the offending drug will usually result in reversal of nearsightedness. Fish oil, Tylenol, and Tums have not been shown to have a correlation with transient myopia development.

An increased rate of molecular movement down its respective concentration gradient via help from carrier proteins refers to which type of transportation?

Facilitated diffusion is described as the net movement of molecules down its concentration gradient whose rate of diffusion is increased via the use of carrier proteins. Passive diffusion refers to the movement of molecules through a plasma membrane from an area of high concentration to an area of low concentration without the use of carrier molecules. Active transport implies the movement of material against its respective concentration gradient. This type of transport requires energy and enlists the use of specific carrier proteins. Lastly, group translocation is defined as the chemical modification of a molecule while it is being transported into a cell; for example, sugars are often phosphorylated during transportation.

A 24-year old female patient presents at your office complaining of side effects that began when she started using Patanol to treat her ocular allergies. She reports complete compliance with her eye drop administration. Which of the following symptoms is MOST likely associated with olopatadine (Patanol) use?

Topical antihistamines and mast cell stabilizers such as Patanol (olopatadine) are commonly prescribed to relieve the symptoms associated with ocular allergies. They are a very effective class of medication due to their dual action mechanisms. Topical antihistamines that possess this dual action are olopatadine (Patanol), ketotifen fumarate (Zaditor), azelastine (Optivar), and epinastine (Elestat). The aforementioned drops serve to alleviate itching and redness by blocking H1 receptors as well as inhibiting mast cell and basophil degranulation. Side effects of topical antihistamine/mast cell stabilizers include stinging upon instillation, headaches, and adverse taste (don't forget to inform your patients about punctual occlusion!). Tachycardia, depression, gastrointestinal discomfort, and visual hallucinations have not been reported with Patanol use.

A 63-year old female is seen at your office with a chief concern of blurry vision in the morning that takes about an hour to resolve before she can see clearly again. Biomicroscopy reveals endothelial guttata. You correctly diagnose her with moderate Fuch's dystrophy. Which ophthalmic drop would be of MOST benefit to her?

Sodium chloride is a topical hyperosmotic agent used to relieve stromal edema caused by endothelial decompensation. Topical steroids work well to decrease swelling caused by inflammation. In the above case, the corneal edema is not mitigated by an inflammatory response. Tobramycin and Vigamox would be of no benefit since there is no active infection, and prescribing either of these would only lead to corneal toxicity or increased pathogen resistance over time.

A deficiency of which vitamin leads to prolonged dark adaptation?

A deficiency of vitamin A causes prolonged dark adaptation. Vitamin A is classified as a retinoid, and its active form is retinol. Retinol is necessary for the formation of rhodopsin, a pigment used by rods. Rods are most active in situations with dim illumination. Less rhodopsin results in fewer rods being able to respond in low levels of light, causing prolonged dark adaption.

+1.50-1.50 x 090 is required to neutralize a reflex in retinoscopy with a working distance of 50 cm. What is the resulting NET retinoscopy finding?

A working distance of 50 cm creates a divergent wave of 2.00 D that is neutralized by retinoscopy in addition to the patient's refractive error. Therefore, + 2.00 D must be subtracted from the spherical portion of the findings. To determine how much to subtract from the gross findings, one must first calculate the reciprocal of the working distance in meters. In our case, 1/0.5 = 2. Therefore +1.50 (the spherical gross findings) -2 = -0.50-1.50 x 090. Remember NET is the final result, this is found after the working distance has been accounted for by subtracting the working distance from the spherical portion of the findings.

A ray of light traveling in water (n=1.33) strikes a flat, transparent surface (n= 1.59) at an angle of 32 degrees from the normal. What is the angle of refraction?

Snell's law of refraction states that when light travels through a material that possesses an index of refraction greater than 1.0, the light rays change direction and become bent (or refracted). Snell's law is depicted as the following: n sin i= n' sin i' where n= the index of refraction of the first medium, i= the angle of incidence, n'= the index of the second medium, and i' = the angle of the refracted ray. All angles are measured with respect to the normal, which lies perpendicular to the interface between the different media. For the above example, 1.33(sin 32)=1.59 sin i', solving for i'= 26.31 degrees. It is important to commit the index of refraction of water to memory; it is 1.33.

A central retinal artery occlusion (CRAO) causes tremendous damage to the retina. How will the electroretinogram (ERG) of a person who has suffered a CRAO be affected?

A central retinal artery occlusion will cause a loss of the b-wave which is formed by responses from the bipolar and Muller cells, both of which are nourished by the central retinal artery. The a-wave results from excitation of the photoreceptors. The a-wave will not be lost in the event of a CRAO due to the fact that photoreceptors receive their oxygen supply via the choroid.

Free radicals can cause severe damage to tissue. Which of the following electrolytes can function as an antioxidant in the aqueous?

The aqueous humor contains many electrolytes including Na+, K+ , Cl-, HCO3-, glucose, lactate, amino acids, and ascorbate. Ascorbate is found in high concentrations in the aqueous (20x greater when compared to the concentration found in plasma). Ascorbate can serve as an antioxidant to eradicate free radicals reducing potential damage from ultraviolet light. Interesting note: the aqueous humor and tears of uncontrolled diabetics display higher levels of glucose than those of non-diabetics.

A 12-year old male is sitting in your waiting room while his mother undergoes her annual eye exam. While waiting, he eats a candy bar containing peanuts, and, as luck would have it, he is deathly allergic to nuts. To counter anaphylactic shock, what would be the BEST course of action?

Anaphylactic shock is defined as a severe, multi-system, type I hypersensitive, acute allergic reaction that may be life-threatening. Signs of an allergic reaction include tingling, itching, hives, swelling of lips and tongue, constriction of the airway, vasodilation, myocardial depression, and a decrease in blood pressure. The EpiPen is injected intramuscularly to the upper lateral thigh to ensure rapid delivery. Epinephrine (Adrenaline) activates both alpha and beta adrenergic receptors causing an increase in peripheral vascular resistance and allowing for an increase in blood pressure and coronary artery perfusion. Adrenaline also serves to reverse vasodilation and decrease urticaria and angioedema. For severe, life-threatening reactions, Benadryl (diphenhydramine) will not work quickly enough. Topical antihistamines have little if any systemic absorption and therefore will not be effective in counteracting the anaphylaxis. While oral steroids may be useful in the post-management of anaphylactic shock, they will not yield the desired immediate response.

An elderly patient presents in your office with decreased visual acuity. He remarks that he can read better without his glasses and his refraction denotes a large myopic shift. Dilated fundus exam is unremarkable. Which of the following slit lamp findings would MOST likely explain the above findings?

Bilateral corneal arcus
Bilateral limbal girdle of Vogt
Bilateral 3+ nuclear sclerosis of the lens
Bilateral crocodile shagreen

Nuclear sclerosis is caused by changes to the optical clarity of the lens. As we age, proteins precipitate out of the lens matrix, causing the lens to become cloudy and altering its density. As time passes, the lens will also begin to change color from clear to a yellow/brown in a process called lens brunescence. Cataracts also generally cause a myopic shift with an increase in against-the-rule astigmatism, leading to decreased distance vision but improved near vision.

Corneal arcus is caused by lipid deposition in the peripheral cornea. There remains a characteristic clear zone between the lipid and the limbus. Arcus does not generally interfere with vision.

Crocodile shagreen and limbal girdle of Vogt are also benign corneal findings commonly seen in the elderly. Crocodile shagreen appears in the peripheral cornea as polygonal white opacities. Limbal girdle of Vogt is noted at the 3 o'clock and 9 o'clock interpalpebral positions as white crescent-shaped opacities.

Long-term use of corticosteroids can lead to the formation of which of the following types of cataract?
Nuclear sclerotic
Posterior subcapsular
Cortical
Anterior subcapsular

The possible formation of posterior subcapsular cataracts (PSC) is a common concern in patients undergoing long-term treatment with corticosteroid therapy. PSCs have been associated with the use of systemic, topical, ophthalmic, topical dermatologic, nasal aerosol, and inhalation type steroids. This relationship is likely dose-dependent, and the usual time from beginning steroid treatment to the onset of lens changes is 1 year (with a dosage of 10 mg/day of prednisone) but has been observed in as short as 2 months with as little as 5 mg/day. Patients with PSC formation may complain of an increase in light sensitivity, photophobia, glare, or difficulty reading. If visual acuity is notably decreased, surgical removal of the lens may be warranted.

Berger's space is created by an interval between which two structures?
The posterior surface of the cornea and the anterior face of the iris
The anterior face of the lens and the posterior surface of the iris
The equator of the lens and the ciliary body
The posterior face of the lens and the anterior vitreous

Berger's space is created by the separation between the posterior face of the lens and the anterior face of the vitreous.

The space between the equator of the lens and the ciliary body is known as the circumlental space.

Patients with a history of homocystinuria are MOST likely to experience crystalline lens subluxation in which of the following directions?
Down and outward
Up and outward
Down and inward
Up and inward

Common ocular sequelae that have been associated with a diagnosis of homocystinuria include ectopia lentis (bilateral crystalline lens subluxation), retinal detachment, and secondary glaucoma. In most cases of ectopia lentis, the lens is more likely to be displaced downward and inward in homocystinuria (as compared to upward and outward in Marfan's syndrome). Additionally, in homocystinuria, the lens zonules are markedly abnormal, the lens does not accommodate, and up to 1/3 of the cases of lens subluxation eventually completely dislocate into the vitreous or anterior chamber. Due to the severity of systemic and cardiovascular complications associated with homocystinuria (thrombosis and occlusion), patients presenting with ectopia lentis should be screened for this disease using the sodium nitroprusside test to measure homocysteine in the urine.

Purkinje images are caused by reflections of objects on the cornea and lens. Which of the four images moves forward with accommodation?
III
I
II
IV

There are four Purkinje images. The first image is caused by reflection from the anterior corneal surface and is the brightest of the images. The first image is roughly the same size as the object. The second Purkinje image is formed by the posterior surface of the cornea and almost coincides with the first Purkinje image. The third Purkinje image is the largest and is caused by reflection off of the anterior plane of the crystalline lens. The fourth Purkinje image is the smallest and is inverted, formed by reflection off of the posterior surface of the lens.

During the process of accommodation the anterior surface of the lens moves forward. The image that is reflected off of this surface is Purkinje III. Purkinje image III will be seen to move forward during accommodation.

The ligaments that suspend the lens (zonules) are embryonically derived from what structure?
The lens capsule
The tertiary vitreous
The lens epithelium
The primary vitreous

The zonules are attached to the posterior and anterior surfaces of the lens and connect to the pars plana of the ciliary body. The primary vitreous develops from weeks 3 through 9. The secondary vitreous then begins to form and condenses the primary vitreous forming Cloquet's canal. Developmentally, the tertiary vitreous is secreted last; the zonules are comprised of condensed tertiary vitreous.

A 42-year old patient reports that her right eye has been watery and she has mild pain, redness, and swelling in the lower medial canthal region. You suspect dacryocystitis as the cause of her symptoms. Which of the following procedures is NOT appropriate when further evaluating this possible diagnosis?
Digital palpation of the medial canthal area
Dilation and irrigation of the lacrimal system
Extraocular muscle motility
Gram stain and blood agar cultures of discharge
Exophthalmometry

The evaluation of a patient suspected of dacryocystitis should involve a detailed case history including a discussion of any previous episodes with similar symptoms, or the presence of any concomitant ear, nose, or throat irritation/infection. External examination of the patient should include the application of gentle pressure to the lacrimal sac region in order to attempt to express any discharge from the punctum; this should be done bilaterally. If any discharge can be recovered, a Gram stain or blood agar culture is helpful in determining the type of bacteria present. In addition to these tests, extraocular motility and evaluation for the presence of proptosis should be completed to rule out orbital cellulitis. In atypical, severe, or non-responding cases, a computed tomography scan (CT) should be considered. It is important to remember that probing, dilation, and/or irrigation of the lacrimal system should not be attempted during an acute infection of the lacrimal gland. This may cause the infection to spread to other areas such as the throat.

A common cause of epiphora in infants is caused by a small membrane that covers over which of the following structures?
The lacrimal gland
The canaliculus
The valve of Hasner
The puncta

It is common for mothers of young infants to note that one eye (or both eyes) of her infant constantly tears in conjunction with the presence of mucopurulent discharge. This epiphora results from a blockage of the nasolacrimal passageway caused by a membrane covering the valve of Hasner. The majority of blockages will self-resolve without intervention (80-90% of infants) within the first 12 months of life. Treatment may include massage of the nasolacrimal sac several times a day in an effort to rupture the membrane.

An 81-year old female reports that her eye has been watering more frequently over the past month; you decide to administer the primary Jones dye test (Jones I). After 5 minutes, the application of a cotton-tipped applicator to the inferior turbinate reveals the presence of dye in the area. Taking this into consideration, what is the MOST likely cause of the patient's epiphora complaint?
Dysfunction of the valve of Hasner
Partial nasolacrimal duct obstruction
Punctal stenosis
Hypersecretion of tears
Complete nasolacrimal duct obstruction

The primary Jones dye test can be utilized to determine the patency of the nasolacrimal system. 1-2 drops of fluorescein are instilled into the inferior fornix of the eyes while the patient is in an upright position and blinking her eyes normally. After a period of 5 to 10 minutes, a cotton-tipped applicator is used to swab the undersurface of the inferior turbinate on each side of the nasal passage.

When the primary Jones dye test is positive (dye is recovered from the inferior turbinate of the nose), practitioners may conclude that the system is patent and that no significant blockage of the nasolacrimal drainage structure is likely. However, minor stenosis or physiologic dysfunctions cannot be completely ruled out. Patients who have a positive result on the Jones I test are more likely to experience symptoms of epiphora that are secondary to primary oversecretion of tears, rather than a dysfunction in lacrimal drainage (as in the above question).

When the primary Jones dye test is negative, the probability of an obstruction or dysfunction in lacrimal drainage is much greater; however, this test alone is not sufficient to document this conclusion. The secondary Jones dye test is then necessary to determine the severity and location of the obstruction.

Oral acyclovir is most effective for patients presenting with eyelid findings associated with herpes zoster if administered within which of the following periods following the onset of the disease?
10-12 hours
72 hours
4-5 days
24 hours
7-10 days

Oral acyclovir is the mainstay of therapy for patients diagnosed with herpes zoster ophthalmicus. This systemic treatment is maximally beneficial if it is initiated within 72 hours from the onset of the disease (usually the appearance of eyelid lesions). The use of oral acyclovir typically results in quick resolution of skin vesicles, decreases the amount of pain the patient experiences, and reduces the duration of viral shedding and appearance of new lesions. Acyclovir has also been shown to significantly reduce the incidence of ocular findings such as episcleritis, keratitis, and iritis. The recommended dosage is 800mg orally 5 times per day for 7-10 days.

Numerous reports have suggested that increased tear film osmolarity is a key consequence in dry eye. Although osmolarity is not easily measured in the clinical setting, tear osmolarity increases in most dry eye sub-types due to which of the following processes?
The lipid layer is altered in most dry eye states, leading to ion pairing
Decreased capillary exchange leads to ionic bonding
Patients with dry eye tend to blink less than normals, leading to increased evaporation
Reactive oxygen species are increased in the tears of most dry eye sub-types; this increases osmolarity
In aqueous tear deficiency, the lacrimal gland produces more ionic species
Loss of tear stability induces an increased evaporation rate, leading to increased osmolarity

Tear instability leads to greater evaporation and higher osmolarity through a mechanism of concentration of the remaining tears, since only the aqueous tear portion evaporates rather than the ionic species. Several studies have indicated that normal tear osmolarity is less than or equal to 300 Osm/L, with values exceeding 308 Osm/L indicating increased osmolarity. As a single measure, tear osmolarity has recently been found to correlate the best (r squared 0.55) to dry eye severity of several clinical tests in a large, multi-center study (Sullivan et al., IOVS 51:6125-6130, 2010).

Many skin anomalies may mimic malignant lesions. Which of the following skin conditions has the HIGHEST risk of becoming malignant?
Cutaneous horn
Papilloma
Actinic keratosis
Seborrhoeic keratosis

Actinic keratosis is a precursor to squamous cell carcinoma and appears as scaly, dry skin that does not heal. People with skin that is of lighter pigmentation along with excessive exposure to ultraviolet light tend to be most at risk for development of this condition.

Papillomas may take on various forms and may be viral or non-viral in origin. They can commonly be found on the eyelids or surrounding orbital skin. Viral warts tend to grow at an accelerated rate while non-viral papillomas are fairly slow to grow. Papillomas can mimic neoplastic growths so be sure to rule this out while watching carefully for color change, ulceration, lash loss, bleeding, and vascularization.

Cutaneous horns or tags are also benign and are likely a form of papilloma but appear to involve more keratin. Treatment is similar to that of a papilloma.

Seborrhoeic keratosis is more commonly seen in middle-aged and elderly persons. This benign, epidermal growth is quite superficial and does not extend into the dermis. It appears like a brown plaque that has been stuck onto someone's skin. The borders are very distinct and there may be some elevation. The lesions may be removed if the patient is concerned about cosmesis.

In addition to the meibomian glands which other accessory glands secrete oil?
Zeiss and Moll
Moll and Krause
Zeiss and Wolfring
Wolfring and Krause

The glands of Zeiss and Moll are accessory oil glands located on the lid margins adjacent to the base of the lash follicles. The lipid layer of the tear film is superficial and as such it is exposed to the environment protecting the aqueous layer from evaporation.

The glands of Wolfring and Krause are located deep in the fornix of the eyelids and serve to secrete a portion of the aqueous layer of the tear film.

Dacryoadenitis refers to an inflammation or infection of which of the following ocular structures?
The nasolacrimal sac
The lacrimal sac
The lacrimal gland
The puncta

Dacryoadenitis describes inflammation of the lacrimal gland, generally due to infection. The swelling is categorized as either chronic or acute. Acute presentations appear more commonly as a unilateral swelling of the upper eyelid, along with pain, excessive lacrimation, probable ipsilateral lymphadenopathy, and potential proptosis. If the condition is bilateral it is likely due to a systemic infection. Chronic dacryoadenitis is generally bilateral and presents with hard masses that are palpable at the location of the lacrimal gland. This form is often painless and caused by inflammatory diseases such as Grave's, Sjogren's, or sarcoidosis. The chronic type warrants further investigation in order to rule out a lacrimal gland tumor.

Chronic blepharitis, if left untreated, can cause which of the following structural changes to the anterior ocular segment?
Hypertelorism
Distichiasis
Tristichiasis
Madarosis

Blepharitis is a condition caused by pathogens, usually of Staphylococcus origin, that colonize along the eyelid margins. The bacteria produce exotoxins which take the form of flakes and are generally seen along the base of the eyelashes. Unfortunately, this condition is chronic but will wax and wane in its presentation. Long-term complications include madarosis (missing lashes), trichiasis, neovascularization of the eyelid margin, keratitis, erythema, phlyctenule formation and infiltrates. Patients may complain of dry, irritated eyes, stinging, pain, itching, frequent eye infections, foreign body sensation, and decreased acuity (if there is corneal involvement). Treatment includes eye lid scrubs, antibiotic ointments and sometimes transient topical steroid use to decrease lid inflammation (usually used in conjunction with a topical antibiotic). Occasionally oral antibiotics are prescribed, especially in the event of poor compliance.

Distichiasis is a rare congenital phenomenon marked by an absence of meibomian glands. In the place of the meibomian glands is an extra row of eyelashes.

Hypertelorism is a term used to describe the incidence in which the orbits are located quite far apart. This generally occurs along with other congenital cranium anomalies.

Tristichiasis is a very rare occurrence in which a person possesses three rows of eyelashes.

Ptosis can be caused by dysfunction or damage to which of the following muscles?
Inferior rectus
Muscle of Horner
Superior tarsal muscle (muscle of Muller)
Pars ciliaris (Riolan's muscle)

Ptosis is a condition in which the upper eyelid sags. It can be caused by dysfunction of either the superior palpebral levator or the superior tarsal muscle (muscle of Muller). Because the levator is the major muscle responsible for raising the upper eyelid, ptosis from levator damage is often more severe then ptosis from dysfunction of the muscle of Muller.

The muscle of Horner (also known as the pars lacrimalis) is part of the palpebral portion of the orbicularis oculi. The fibers for the muscle of Horner come from the lacrimal crest and encircle the lacrimal canaliculi. This assists the flow of tears into the nasolacrimal drainage system when the orbicularis oculi contracts to close the eye. The muscle of Riolan (also known as the pars ciliaris) is another section of the palpebral portion of the orbicularis oculi; it lies near the lid margin to maintain the margins next to the globe. The orbicularis oculi is the major muscle responsible for closing the eyelids.

Tear volume in a normal, healthy, young adult measures approximately between which of the following values?
13.0-16.0 microliters
6.0-8.0 microliters
17.0-20.0 microliters
2.0-5.0 microliters
9.0-12.0

Tear volume has been measured by several methods to be approximately 6-7 microliters in normal individuals, with lesser values occurring in conditions of aqueous tear deficiency. This has implications for drug delivery, since the normal ophthalmic drop volume varies between 25 and 50 microliters, effectively overwhelming the native tear value upon instillation.

The lymphatic system serves many important roles in the human body. The lateral portion of the eyelid lymphatics drain into which of the following structures?
The puncta
The conjunctiva
The submandibular lymph node
The pre-auricular lymph node

The lateral 2/3 of the upper lid and the lateral 1/3 of the lower lid lymphatics drain into the pre-auricular lymph node located directly in front of the ear. The medial 1/3 of the upper eye lid and the medial 2/3 of the lower lid lymphatics drain into the submandibular node located just under the jaw-line. Therefore, it is very important to evaluate these two nodes separately, especially when a condition of viral etiology is suspected.

A 2.5x Galilean telescope has a -25D ocular lens. When focused for infinity, what is the length of the telescope?
5 cm
4 cm
6 cm
10 cm
14 cm

M = -Doc/Dobj where Doc=power ocular; Dobj= power objective; t= separation of lenses
2.5= - (-)25/Dobj
Dobj= 10D
t= f'obj + f'oc
f'obj=1/10D = 0.10 m
f'oc = 1/-25D = 0.04 m

t=0.10 + -0.04 = 0.06 m or 6 cm

10 cm - incorrect- would come up with this answer if only took in account the focal length of the objective lens.
4 cm - incorrect- would come up with this answer if only took in account the focal length of the ocular lens.
14 cm - incorrect - would come up with this answer if thought equation was t= f'obj + f'oc

A patient is using a stand magnifier of +16D with a +2.00 add. If the distance separating the two lenses is 25 cm what is the equivalent power of this combination?
10D
18D
26D
22D

De= D1+D2 -tD1D2 where De=equivalent power;D1=power of magnifier;D2=power add;t=separation in meters between the lenses
De = (16+2) - 0.25(16)(2) De= 18-8 = 10D
18D- incorrect answer -would come up with this if added the stand magnifier power to the power of the add
22D -incorrect answer - would come up with this if added 16D for stand mag 2D for add and 4D for equivalent of 25cm.
26D - if added the 18 +8 in the De equation instead of subtracting

Illumination is one of the most important considerations to discuss in the case disposition for a visually impaired patient. A patient with chronic open angle glaucoma moves a 60 watt bulb on a flexible mounted arm from three feet to one foot from the page. The illumination on the page will appear to have been increased by how much?
Should be the same brightness
Increased by 3 times the original brightness
Decreased by 1/3 of the original brightness
Decreased by 1/9 of the original brightness
Increased by 9 times the original brightness

It has been said that prescribed optical devices without consideration of the appropriate lighting will often doom the patient to failure. Unfortunately, there are no good tests to determine the exact type of lighting. Generally, different light levels are tried during the examination (as well as during the training session) with the patient using an adjustable light. The distance from the page is very important because of the inverse-square law of illumination: the intensity varies inversely as the square of the distance from the page. If the light is moved from 1 foot to 3 feet from the page, a bulb will be needed that is approximately nine times as bright to keep the same illumination on the page. (It should be noted that technically, this relationship is only true for a point source of light.) Clinically, however, it gives a good approximation of the change in brightness (illumination) seen on the page when the distance of the light is changed. The illumination in the above example would therefore increase by 9X when the bulb is moved towards the page.

One of your tech-savvy low vision patients wishes to use a CCTV for reading. The CCTV operates on what principle of magnification?
Rated magnification
Equivalent magnification
Relative distance magnification
Relative size magnification

CCTVs work on the principle of relative size magnification (or projection). It operates by enlarging the text without lenses in front of the patient or the patient moving closer to the device. When the print is enlarged electronically in this matter, the image of the print subtends a larger area on the retina and thus a larger size.

An example of relative distance magnification would be if you were holding a newspaper at 40 cm and you moved it closer to 20 cm. The print now appears 2 times as large relative to the 40 cm distance.

Rated magnification is often used by manufacturers of some hand magnifiers and stand magnifiers using a 25 cm reference distance.

The visual acuity of a 77 year-old female patient with age-related macular degeneration is 2/16 in the right eye on the ETDRS chart. Why is this chart useful in monitoring the response to treatment with anti-vascular endothelial growth factor (VEGF)?
A three-line decrease represents a factor of a two time decrease in the size of the letters
Each line is 1.0 log units larger than the previous line
The Snellen construction of the chart enables the examiner to quickly note that a two-line increment represents a factor of a two time increase in the size of the letters
Each line has 5 Sloan letters throughout the chart with equal spacing and is 1.26 times larger than the line below it; each line is .1 log units larger than the line below it when moving up the chart

The ETDRS chart is a logarithmic eye chart modeled after the Bailey-Lovie chart. It is the primary standardized eye chart used in evaluating the visual acuity of low vision patients. The ETDRS charts are logMAR (log of the minimum angle of resolution) in design and are constructed with 10 Sloan sans serif letters. Each line is 1.26 times larger than the line below, and the construction of each line is such that the difficulty is theoretically equivalent on every line.

The construction of the ETDRS chart is made to eliminate the inherent errors in the measurement of visual acuity found in the traditional non-standardized Snellen test charts. The Snellen test charts have variations in legibility of different letters as well as differences in the spacing between the lines of letters and between adjacent letters on single lines. The ETDRS logarithmic chart is constructed in such a way that each line of letters is 0.1 log units (about 1.26 times) larger than the previous line. This is a geometric progression.

A positive catalase test indicates that a bacteria is capable of breaking down which of the following?
Pyruvate
Glucose
Carbon dioxide
Hydrogen peroxide

Catalase is an enzyme commonly found in organisms that are exposed to oxygen. Catalase breaks down hydrogen peroxide into oxygen and water. The catalase test is performed by applying a drop of hydrogen peroxide to a microscope slide. A colony of bacteria is then exposed to the hydrogen peroxide via an applicator stick. The presence of bubbles or froth yields a positive catalase test. Staphylococci and Micrococci are catalase-positive organisms. Campylobacter and Escherichia coli are catalase-negative organisms.

Antibiotic resistance that is rapidly spread within a population of bacteria is due to what mechanism?
Transformation
Budding
Conjugation
Binary fission

Conjugation occurs between a donor (possesses a conjugative plasmid) and recipient bacteria. The donor bacterium initiates contact with the recipient via a sex pilus, allowing for cell-to-cell contact and transfer of DNA. The plasmids often contain genes that encode for toxin production, virulence factors, and antibiotic resistance. Genetic transformation is achieved by very few strains of bacteria and may only occur during certain phases of growth; therefore, rapid antibiotic resistance is not feasible. Budding and binary fission are means of reproduction but are not directly responsible for antibacterial resistance. Genes must have been transferred that code for resistance prior to budding and binary fission in order for the progeny to contain genes that allow for drug resistance.

Congenital cataracts can be caused by a viral infection of the mother with rubella virus (German measles) during development of the primary lens fibers. At which time period in embryonic development can infection cause congenital cataracts?
Conception
1st trimester
3rd trimester
2nd trimester
Post-delivery

The developing lens is susceptible to rubella virus when the lens fibers are forming, which occurs around weeks 4-7 of gestation. Earlier infection will occur prior to lens fiber development, and the lens is resistant to later infection because the virus is unable to penetrate the lens capsule.

The fetus is most susceptible to lenticular damage during the first trimester. Contraction of the rubella virus will cause the greatest amount of damage during this time period. Congenital cataracts are usually detectable at birth but may be seen later because the virus can persist in the lens.

A 12-year old male is sitting in your waiting room while his mother undergoes her annual eye exam. While waiting, he eats a candy bar containing peanuts, and, as luck would have it, he is deathly allergic to nuts. To counter anaphylactic shock, what would be the BEST course of action?
Prednisone (oral)
Administration of Benadryl (oral)
Olopatadine (Patanol)
Injection of epinephrine (EpiPen)

Anaphylactic shock is defined as a severe, multi-system, type I hypersensitive, acute allergic reaction that may be life-threatening. Signs of an allergic reaction include tingling, itching, hives, swelling of lips and tongue, constriction of the airway, vasodilation, myocardial depression, and a decrease in blood pressure. The EpiPen is injected intramuscularly to the upper lateral thigh to ensure rapid delivery. Epinephrine (Adrenaline) activates both alpha and beta adrenergic receptors causing an increase in peripheral vascular resistance and allowing for an increase in blood pressure and coronary artery perfusion. Adrenaline also serves to reverse vasodilation and decrease urticaria and angioedema. For severe, life-threatening reactions, Benadryl (diphenhydramine) will not work quickly enough. Topical antihistamines have little if any systemic absorption and therefore will not be effective in counteracting the anaphylaxis. While oral steroids may be useful in the post-management of anaphylactic shock, they will not yield the desired immediate response.

A Galilean telescope has an ocular lens with a power of -32.00 D and an objective lens with a power of +8.00 D. What is the magnification provided by the telescope?
256x
8x
0.25x
4x

To calculate the magnification (M) of a telescope divide the power of the ocular lens (Doc) by the power of the objective lens (Dobj): M=-Doc/Dobj. In the example above, M=-(-32 D)/8 D= 4x. The magnification of a Galilean telescope is positive due to the fact that its ocular has a minus powered lens. The magnification of an astronomical telescope is negative and therefore its image will be upside down.

A 6-foot tall man wishes to buy a plane mirror in which he can visualize his whole length at the same time. How tall must the mirror measure in order for the above to occur?
3 feet tall
6 feet tall
5.2 feet tall
4.5 feet tall
2.3 feet tall

In order for a person to see their entire reflection, a plane mirror must be half as tall as the person. This holds true regardless of the position of the person. For the above example, 6/2= 3 feet.

A convex mirror in water (n=1.33) has a radius of curvature of 12 cm. What is the dioptric power of the mirror?
-22.17 D
-11.08 D
+22.17 D
+8.33 D

A concave mirror converges light and therefore acts like a convex lens, hence concave mirrors have positive dioptric values whereas convex mirrors diverge light and possess negative dioptric powers.

The equation used to determine the power of a mirror is P=-2n/r, where P= the power of the mirror in diopters, n= the index of refraction of the surrounding medium, and r= the radius of curvature of the mirror in meters. P=2(1.33)/-0.12=-22.17 D. Remember, a convex mirror will have a positive radius of curvature and a concave mirror will have a negative radius of curvature.

A patient is seen at your office complaining that her right eye is physiologically higher than her left eye. She would like to know if glasses would help improve the cosmesis of her predicament. You know that prism will shift the image of an object. How would you orient a prism to help her appearance?
Prescribe base out prism over the left eye
Prescribe base in prism over the left eye
Prescribe base down prism over the left eye
Prescribe base up prism over the right eye

A prism will bend light towards its base, but the image will be shifted towards the apex of the prism. Therefore, by prescribing base up prism over her right eye, its image will be shifted down towards the apex of the prism. Another way of remembering this is to think of the prism as an arrow that will point in the direction of the deviation (i.e., exotropia is neutralized with base in prism, the eye points outwards, the apex of the prism also points out). Prescribing prism for cosmetic purposes may not always be an option as significant vertical prism may induce diplopia or visual discomfort.

A patient brings you an old pair of glasses and asks you how much prism is in the lenses. With the lensometer, you measure 7 prism diopters base up and 4 base out in the right eye and 4 prism diopters base up and 5 base out in the left eye. What is the total amount of prism in the glasses?
11 prism diopters base up total and 9 base out
3 prism diopters base up in the right eye and 1 base out
3 prism diopters base up in the right eye and 9 base out
11 prism diopters base up total and 1 base out

For vertical prism, if the bases are oriented in the same direction, they will cancel each other out. When the bases are oriented in opposite directions in the vertical meridian (i.e., base up and base down), the powers will add together. The opposite holds true for prisms with their bases oriented horizontally. If the prism bases are both base out or base in, the powers are additive, while if they are opposite (that is, one is base in and one is base out), the powers will cancel.

A patient returns to your office reporting that her eyes feel strange when she reads 6 mm below the optical centers of her new glasses. The prescription in her right eye is -4.00 DS and -7.00 DS in her left eye. How much vertical prism is induced when she reads?
4.2 prism diopters base down
1.8 prism diopters base down
2.4 prism diopters base down
6.6 prism diopters base down

Use the Prentice rule to solve this problem: prism diopters(pd) =d*F, where d= the distance from the optical center in centimeters and F= the power of the lens in the desired meridian in diopters. In this instance, the patient is looking through base down prism in both eyes, which will cancel some of the prismatic effect as the bases are aligned. Solving for the amount of prism on the right eye, pd=0.6(-4.00)= 2.4 base down prism. Solve for the left eye: pd=0.6(-7.00)=4.2 base down prism. Subtract the two to determine the total prismatic effect experienced by the patient: 4.2-2.4=1.8 base down prism. Alternatively, you can omit one of the steps by initially determining the total power difference in the vertical meridian between the two lenses, which is 3.00 D (7-4=3). Then you can multiply this power difference by the distance between the patient's line of sight and the optical center, which is 6 mm in this question. Pd=0.6(3)= 1.8 prism diopters base down over the left eye. Generally, vertical imbalances of smaller magnitudes do not pose too much of a problem for single vision lenses as the patient can tilt her head to re-align the optical centers with her line of sight, thus eliminating any possible diplopia.

A chiasmal lesion or mass, such as a pituitary tumor, generally causes what type of visual field defect?
Left homonymous hemianopsia
Right homonymous hemianopsia
Binasal heminopsia
Bitemporal hemianopsia

The center of the chiasm contains axons of decussating ganglion cells that originate from the nasal retinas, which process temporal visual field information. The lateral portion of the chiasm is comprised of the axons of the temporal aspect of the retinas, which do not cross over. Lesions most commonly occur in the central portion of the chiasm and not the lateral aspects. Any central chiasmal mass or lesion will cause a bitemporal visual field defect that respects the vertical midline.

A cranial nerve VI palsy will cause what type of deviation?
Exodeviation worse with distance viewing
Esodeviation worse with distance viewing
Esodeviation worse with near viewing
Exodeviation worse with near viewing

A cranial nerve (CN) VI palsy, or a palsy of the abducens nerve, will cause an esodiviation on the affected side and will result in horizontal diplopia, which worsens with distance viewing since this nerve innervates the lateral rectus muscle. The patient may present with a head turn towards the same side as the affected eye. For instance, if the patient has a right lateral rectus palsy, he or she may present with a head turn to the right to help eliminate diplopia. It helps to think in terms of function. The lateral recti serve to abduct the eyes, and distance viewing requires divergence, or a turning out of both eyes simultaneously. A CN VI palsy will therefore be more evident when the patient looks far away, because the eye cannot abduct.

A healthy retinal nerve fiber layer is thickest at which portion of the optic nerve head?
Nasally
Inferiorly
Superiorly
Temporally

The nerve fiber layer is thickest at the inferior and superior regions of the nerve, respectively. The inferior and superior arcades are composed of large diameter axons with little overlap of the receptive fields, thus explaining why a field defect occurs in these regions first for early cases of glaucoma. Inferior or superior notching of the nerve is highly suspect for glaucomatous damage, and must undergo further testing in order to rule out glaucoma. The next thickest area of nerve fiber layer tissue is nasally, which is comprised of the nasal radial fibers. These axons are affected in the later stages of glaucoma, thus explaining why a temporal island of the visual field is often left remaining in advanced cases of glaucoma. Lastly, the temporal rim area is the thinnest. Temporal rim tissue is comprised of the papillomacular bundle. The fibers in this area are very small and compact, with a high degree of receptive field overlap, therefore because of the receptive field redundancy, a visual field defect correlating to this region will occur only after significant fiber loss has occurred. Due to the fact that these fibers are so small in diameter, even though they are numerous, the fibers do not occupy a lot of space in the optic nerve. The thickness of the nerve fiber layer rim tissue is best remembered as ISNT, with inferior being the thickest and temporal rim tissue being the thinnest.

A patient is seen at your office reporting constant diplopia. The patient notes that the diplopia is still present when you cover her right eye. Based upon this information, what is the MOST likely etiology of her diplopia?
Uncorrected refractive error
Superior oblique palsy
Lateral rectus palsy
Aneurysm

Monocular diplopia is never caused by any type of cranial nerve dysfunction. The most common cause of monocular diplopia is an uncorrected refractive error. Other causes of monocular diplopia include corneal irregularities, lens irregularities, lens subluxation (very rare), or an improper glasses prescription. Whenever you are confronted with a recent onset of diplopia, the first thing you must determine is whether the diplopia is present monocularly or binocularly.

A cortical hypercolumn is comprised of which of the following?
An ocular dominance column for one eye only and orientation columns for one specific orientation only
An ocular dominance column for one eye only and a complete set of orientation columns
Ocular dominance columns for both eyes and orientation columns for one specific orientation only
Ocular dominance columns for both eyes and a complete set of orientation columns
A complete set of ocular dominance columns for one eye only and a complete set of orientation columns

The striate cortex is organized into discrete rows and columns that help to code for specifics of the stimulus. A hypercolumn consists of both a right and left eye ocular dominance column as well as orientation columns for every orientation. An electrode that penetrates the cortex perpendicularly will encounter cells with the same ocular dominance, and they all respond to stimuli of the same orientation. However, an electrode that penetrates the cortex parallel to its surface will encounter neurons that all possess the same ocular dominance but respond preferentially to stimuli of different orientations. In order for ocular dominance columns to form properly, it is essential that normal vision is present in both eyes during the early years of life.

A patient who has a high spatial frequency cut-off of 40 cycles per degree will have what predicted Snellen acuity?
20/30
20/40
20/20
20/15

In order to convert from cycles per degree to Snellen acuity, simply divide 600 by the cycles per degree; this will solve for the denominator of the Snellen acuity. For the above example 600/40 = 15. Therefore, the predicted Snellen acuity would be 20/15.

A person can just barely detect the difference between two weights; one weighs 12 pounds and the other weighs 10 pounds. What is the just noticeable difference for a weight of 70 pounds?
2 pounds
20 pounds
8 pounds
56 pounds
14 pounds

Weber's Law deals with the just noticeable difference and can be expressed mathematically as:
K= delta I/I, where K= Weber's constant, delta I= that difference threshold, and I= the original stimulus intensity (weight etc.)

For the above example, we must first solve for Weber's constant. 12-10/10=0.2. Using this Weber's constant we can then solve for the just noticeable difference or the increment threshold for 70 pounds.
X-70/70=0.2, X= 14 pounds. Therefore, the above person will just be able to discern the difference between a 70-pound weight and an 84-pound weight.

A person who is missing the photopigment chlorolabe is categorized as which of the following?
A protanope
A deuteranomalous trichromat
A tritanope
A protanomalous trichromat
A deuteranope

There are several classifications of color-vision defects; hereditary defects are the most common. The two broad categories are dichromacy and anomalous trichromacy. In dichromacy, one of the photopigments is missing; the type of dichromacy is categorized based on which photopigment is lacking. A deuteranope is missing chlorolabe, a tritanope is missing cyanolabe, and a protanope is missing erythrolabe. It is theorized that the missing photopigment is replaced by the photopigments that are present; otherwise, the person would likely suffer a deficit in visual acuity. Anomalous trichromats are in possession of all three photopigments but the absorption spectrum of one of the pigments has been shifted. For a protanomalous trichromat, the spectrum for erythrolabe is shifted towards the shorter wavelengths. A deuteranomalous trichromat displays a shift of the maximum sensitivity of chlorolabe towards the longer wavelengths. Protans and deutans are said to be red-green colorblind while tritans tend to mix up blues and yellows and are said to possess a blue-yellow defect; this is usually acquired rather than hereditary.

A 24-year old female patient presents at your office complaining of side effects that began when she started using Patanol® to treat her ocular allergies. She reports complete compliance with her eye drop administration. Which of the following symptoms is MOST likely associated with olopatadine (Patanol®) use?
Gastrointestinal discomfort
Headache
Depression
Tachycardia
Visual Hallucinations

Topical antihistamines and mast cell stabilizers such as Patanol® (olopatadine) are commonly prescribed to relieve the symptoms associated with ocular allergies. They are a very effective class of medication due to their dual action mechanisms. Topical antihistamines that possess this dual action are olopatadine (Patanol®), ketotifen fumarate (Zaditor®), azelastine (Optivar®), and epinastine (Elestat®). The aforementioned drops serve to alleviate itching and redness by blocking H1 receptors as well as inhibiting mast cell and basophil degranulation. Side effects of topical antihistamine/mast cell stabilizers include stinging upon instillation, headaches, and adverse taste (don't forget to inform your patients about punctual occlusion!). Tachycardia, depression, gastrointestinal discomfort, and visual hallucinations have not been reported with Patanol® use.

A 31-year old male patient presents to your office for a photorefractive keratectomy (PRK) pre-operative examination. As you review his required ocular medication schedule, which of the following prescribed drops must you remember to tell him to "shake well" before instillation?
Zymaxid®
FreshKote®
Pred Forte®
Acular®

Pred Forte® is an ocular medication that is in suspension form; therefore, it is important to shake this medication well before use. Other forms of prednisolone that are suspensions include Pred Mild®, Econopred®, and Econopred Plus®.

On the other hand, there are prednisolone ocular medications that are solutions, making shaking of the bottle unnecessary. These include AK-Pred®, Inflamase Mild®, and Inflamase Forte®.

Zymaxid® is a 4th generation fluoroquinolone antibiotic that is bottled in solution form, as well as Acular®, which is an ocular non-steroidal anti-inflammatory drug (NSAID). FreshKote® is a prescription artificial tear that also does not need to be shaken before use.

A 32-year old female is seen at your office complaining of a recent onset of blurred vision, only at a distance. A thorough case history reveals that she recently began taking a new medication which you correctly assume has induced myopia. Which of the following medications is MOST likely to be the culprit?
Tums® (calcium carbonate)
Accutane® (isotretinoin)
Tylenol® (acetaminophen)
Omega III fish oil capsules

Isotretinoin, birth control pills, and diuretics, among many other drugs, can cause myopia in some patients. Myopia most likely results from corneal swelling, which steepens the curvature of the cornea. Drugs that cause swelling of the lens, accommodative spasm, or edema of the ciliary body will also result in myopia. A reduction in the dose of the medication or cessation of the offending drug will usually result in reversal of nearsightedness. Fish oil, Tylenol®, and Tums® have not been shown to have a correlation with transient myopia development.

A chin fissure is a dominant trait. If a father who is homozygous-dominant for this trait and a mother who is homozygous-recessive for this trait mate, what are the chances that their first child will have a chin fissure?
50%
0%
25%
100%
75%

Because the father is homozygous-dominant, it is indicated that he possesses a dominant gene pair for the chin fissure trait (FF). On the other hand, the mother is homozygous-recessive for this trait; therefore, phenotypically she would have a "normal chin" because she has an identical gene pair that does not code for a chin fissure (ff). Each child would receive an allele from each parent, but the pair of genes would not be identical (this is termed heterozygous (Ff)).

However, because they would inherit a dominant form of the allele, this is the form of the gene that would influence the phenotype, resulting in the appearance of a chin fissure.

A constant ringing of the ears is known as which of the following terms?
Malleus
Sinusitis
Otitis media
Tinnitus

Tinnitus is caused by damage to hair cells in the inner ear from exposure to excessive noise, medications (like aspirin), aging, and some diseases. Sound waves cause the hair cells to bend, releasing a neurotransmitter and causing action potentials of the auditory nerve. Sometimes the hair cells break or are left in the "on" position, causing the perception of ringing.

Otitis media is an infection or inflammation of the middle ear.

Sinusitis is an inflammation of the sinuses.

The malleus, also known as the hammer, is one of the tiny bones in the ear that help to transmit and amplify sound to the auditory nerve.

A contracting muscle that develops tension but does not shorten displays which type of muscle tension?
Isometric
Isovelocity
Isotonic
Isovolume

Isometric contraction occurs when a muscle is contracting but is not shortening. This type of muscle tension is used for load-bearing situations such as holding a plate of food in front of you. Muscles that shorten but maintain the same amount of tension are said to display isotonic contraction. An isovelocity contraction follows when the force of the contraction varies while the velocity remains constant.

During gestation, when does the secondary vitreous begin to develop?
The 20th week of gestation
The 30th week of gestation
The 9th week of gestation
The 1st week of gestation

The primary vitreous develops at around the third week of gestation. It is formed by mesoderm. The secondary vitreous begins to develop during the ninth embryonic week and later becomes the mature vitreous. The secondary vitreous stems from primary vitreal cells and retinal glial cells and therefore originates from neuroectoderm. The secondary vitreous expands to fill the globe while compacting the primary vitreous in the center of the globe.

A central retinal artery occlusion (CRAO) causes tremendous damage to the retina. How will the electroretinogram (ERG) of a person who has suffered a CRAO be affected?
The a-wave will remain while the b-wave will disappear
Both the a-wave and the b-wave will remain
Both the a-wave and the b-wave will disappear
The a-wave will disappear while the b-wave will remain

A central retinal artery occlusion will cause a loss of the b-wave which is formed by responses from the bipolar and Muller cells, both of which are nourished by the central retinal artery. The a-wave results from excitation of the photoreceptors. The a-wave will not be lost in the event of a CRAO due to the fact that photoreceptors receive their oxygen supply via the choroid.

A patient is concerned with an acute reduction of the acuity in the right eye. You correctly diagnose central serous retinopathy, and confirm your diagnosis with an optical coherence tomography (OCT). What is the standard treatment protocol?
Monitor monthly for resolution
Refer for intravitreal steroid injection
Treat the patient with prism as they are likely to develop diplopia
Refer for laser treatment of the retina
Refer for cryotherapy of the retina

CSR is more commonly seen in middle-aged males under high-stress, who are very anxious, or with type A personalities. This condition causes fluid to leak from the choriocapillaries into the subretinal area, causing a serous detachment of the neurosensory retina. There is an associated loss of the foveal reflex, a hyperopic shift, a potential relative scotoma, and metamorphopsia. Flourescein angiography will reveal hyperfluorescence that appears like a smoke-stack. Evaluation of the posterior pole will typically display a blister-like elevation of the neurosensory retina. The patient is monitored monthly and intervention is rarely required, as most cases of CSR will resolve within roughly 6 months.

According to the Keith-Wagener-Barker method of classification, hypertensive retinopathy is categorized as stage four when which ocular sign is present?
Hard exudates in a star configuration
Swelling of the optic disc
Flame hemorrhages
Retinal edema

Grading of hypertensive retinopathy according to the Keith-Wagener-Barker system is as follows:
Stage 1- narrowing of the retinal arteries
Stage 2- stage 1, plus focal constriction of the retinal vasculature (arteriovenous nicking)
Stage 3- stage 2, plus retinal hemorrhages, hard exudates (likely in a star configuration), cotton wool spots, and retinal edema
Stage 4- stage 3, plus swelling of the optic disc. This patient must be hospitalized immediately.

Bipolar cells receive information from photoreceptors. Which type of neurotransmitter do bipolar cells respond to?
Glycine
Glutamate
Serotonin
Dopamine

Bipolar cells respond to glutamate released by photoreceptor cells. Glutamate release in the dark causes on-center bipolar cells to hyperpolarize (inhibition) and off-center bipolar cells to depolarize (excitation).

Drusen typically deposit between which layers of the retina?
The inner and outer plexiform layers
The ganglion cell layer and the nerve fiber layer
The retinal pigment epithelium and Bruch's membrane
The inner and outer nuclear layers

Drusen deposits collect between the retinal pigment epithelium (RPE) and Bruch's membrane. The retinal pigment epithelium plays a very important role in phagocytosis of shed outer segments of photoreceptors. If the RPE fails to rid the retina of this debris, it will begin to accumulate, which can have a significant impact on vision and may lead to macular degeneration.

Midget ganglion cells receive information pre-synaptically from which cells?
Horizontal bipolar cells
Rod bipolar cells
Midget bipolar cells
Flat bipolar cells

Midget bipolar cells synapse onto midget ganglion cells. These are very selective and exclusive channels as one cone cell synapses with one midget bipolar cell which then in turn relays the information to a midget ganglion cell. There is no additional input from other cells or synapses. These types of monosynaptic cells are most common in the central retina thus explaining the ability to visually discern fine details.

Flat bipolar cells receive information from many cone cells and in turn synapse with many ganglion cells.

Rod bipolar cells, as their name suggests, convey information from many rod cells to several ganglion cells. Rods relay information only to rod bipolar cells.

What is the MOST common type of oculomotor deviation?
Exophoria
Hyperphoria
Hypophoria
Esophoria

By far the most common oculomotor deviations are exo in nature ( about 95%), however most do not pose a problem. The least common type of deviation is vertical.

While examining a patient with diplopia, you ask him to look downward and toward his nose. He is able to move the eye toward his nose (medially) but not down. Based on the isolated agonist model of eye movement by extraocular muscles, which nerve and muscle are not functioning appropriately?
Oculomotor nerve, superior rectus
Trochlear nerve, inferior oblique
Abducens nerve, lateral rectus
Abducens nerve, inferior oblique
Trochlear nerve, superior oblique

The trochlear nerve (CN IV) innervates the superior oblique muscle. The abducens nerve (CN VI) innervates the lateral rectus, which is not involved in the motion described in this question. The oculomotor nerve has two divisions; the inferior division innervates the inferior rectus, inferior oblique and medial rectus, while the superior division innervates the superior rectus and levator palpebrae superioris.

The functions and anatomy of the extraocular muscles are as follows:
Superior rectus - turns eye up, adducts, and medially rotates (intorsion)
Inferior rectus - turns down, adducts, and laterally rotates (extorsion)
Lateral rectus - abducts eye (laterally)
Medial rectus - adducts eye (medially)
Superior oblique - medially rotates (intorsion), abducts and turns eye down
Inferior oblique - laterally rotates (extorsion), abducts and turns eye up

In the case described here, when the patient adducts the eye medially with the medial rectus as well as the superior and inferior rectus, only the superior oblique and inferior oblique can move the eye down or up respectively because the superior and inferior rectus muscles are already contracted. The same is true if a patient abducts the eye with the obliques and lateral rectus: only the superior and inferior rectus can move the eye up or down respectively.

Which of the following muscle pairings and actions follows Sherrington's law of reciprocal innervation?
Looking to the right causes contraction of the right medial rectus and contraction of the left medial rectus
Looking to the right causes contraction of the right medial rectus and inhibition of the right lateral rectus
Looking to the right causes contraction of the right lateral rectus and inhibition of the left medial rectus
Looking to the right causes contraction of the right lateral rectus and inhibition of the right medial rectus

Sherrington's law of reciprocal innervation states that when a muscle is stimulated to contract, its antagonist is inhibited. Based upon this law, looking to the right causes contraction of the right lateral rectus and inhibition of the right medial rectus.

Which extraocular rectus muscle has its insertion site CLOSEST to the limbus?
The superior rectus
The inferior rectus
The lateral rectus
The medial rectus

The medial rectus inserts into the sclera roughly 5.3 mm from the limbus, followed by the inferior rectus, which inserts 6.8 mm from the limbus. The lateral rectus inserts 6.9 mm from the limbus, and the superior rectus has the furthest insertion point at 7.9 mm from the limbus. Remember MILS (Medial rectus, Inferior rectus, Lateral rectus, Superior rectus). If one draws a line connecting the insertion points of the muscles, an imaginary spiral is created called the spiral of Tillaux.

Reference: Chen, W. Oculoplastic Surgery: the Essentials (2001) page 330.

When performing a unilateral cover test on your patient, you note the following: upon covering the right eye, the left eye moves in 1/10 times. Upon covering the left eye, the right eye moves in 4/10 times. The alternating cover test measures 25 prism diopters base-in. What is your diagnosis based on these findings?
25 prism diopter intermittent alternating exotropia; left eye preferred
25 prism diopter intermittent alternating esotropia; left eye preferred
25 prism diopter intermittent alternating esotropia; right eye preferred
25 prism diopter intermittent alternating exotropia; right eye preferred

The unilateral cover test will tell you the eye (or eyes) affected, the direction, and the frequency of the ocular deviation. In this case, the eyes lose fixation 5/10 times, which shows that the frequency is intermittent (it would be constant if at least 1 eye moved 10/10 times). Since each eye moves at least once when the other is covered, the deviation is considered to be alternating. The uncovered eye is noted to move "in" on unilateral cover test, meaning that the deviation is an exotropia (if the eye moves "out" it is an esotropia). Since the right eye loses fixation more than the left eye (4/10 vs. 1/10), the left eye is considered to be the preferred eye. Also, the alternating cover test will tell you the full amount of the deviation, which is 25 prism diopters in this case.

Which of the following conditions would be categorized as causing amblyopia due to deprivation?
A child born with a large congenital cataract in one eye only
A child born with a monocular 2 mm ptosis
A five-year old with an uncorrected prescription of OD: +7.00 D 20/400 OS: +0.50 20/20
A three-year with a constant right 30 prism diopter esotropia

Form deprivation amblyopia results when a clear and focused retinal image is blocked to one eye during the critical period. This can occur by a complete congenital cataract in one eye, a large ptosis that covers most or all of the pupil or by some other element that occludes the eye. The lack of visual information to the retina causes the other eye (non-occluded eye) to become dominant and thusly have stronger and a greater number of synaptic connections to the brain. Amblyopia causes a disproportionate amount of cortical neurons to respond preferentially to the non-deprived eye. The occlusion must occur during the critical period, and the earlier the occlusion is detected and removed, the better the prognosis. A small ptosis (i.e. 2 mm) would not be expected to cause amblyopia because the pupil would not be occluded. An unequal prescription such as the one in the above question would cause anisometropic amblyopia in which one eye would receive a clear image while the other would receive a blurry image. The brain would favor the clear retinal image, resulting in a strong dominance of cortical neurons for the least ametropic eye. Strabismus results in the perception of two images that are not fusible by the brain, causing diplopia. In order to eliminate double vision, the eye will suppress an eye (usually the deviated eye). This suppression leads to amblyopia.

Which of the following methods can be used to test for the presence of eccentric fixation?
Binocular versions
The Hirschberg test
The Bruckner test
Visuoscopy

Angle Kappa (Lambda), visuoscopy, Haidinger's Brush, and the Brock-Givner afterimage transfer tests are all methods of investigating for the presence of monocular fixation. The Hirschberg test allows for the determination of the direction, magnitude, and frequency of the ocular deviation. The Bruckner test may be used to detect small angle deviations, media opacities, anisometropia, and tumors. Binocular versions allows for the determination of the comitancy of the deviation.

Which of the following types of refractive error would have the greatest tendency to lead to amblyopia?
A four-year old boy with an uncorrected refractive error of OD: +6.00 DS and OS: +1.50 DS
A five-year old girl with an uncorrected refractive error of OD: -3.25 DS and OS: -0.75 DS
A four-year old girl with an uncorrected refractive error of OD: +1.00-1.50 x 180 and OS: +1.50-1.25 x 180
A three-year old boy with an uncorrected refractive error of OD: +1.50 DS and OS: -2.00 DS

A prescription in which there is a big refractive difference between the eyes, especially if both eyes are hyperopic, is most likely to cause amblyopia. Consider the prescription of OD: +6.00 DS and OS: +1.50 DS. The left eye will be able to accommodate 1.50 diopters to obtain a clear distance image and, because accommodation is bilateral and equal, the right eye will still be 4.50 diopters out of focus. This defocus will cause the left eye to dominate the cortical neurons, causing a decreased amount of binocular neurons and leading to poor stereopsis and amblyopia of the right eye.

A prescription of OD: -3.25 DS and OS:-0.75 DS will not lead to amblyopia because even though the right eye is blurry in the distance, at 30 cm its image will be clear and in focus. This also applies to the prescription of OD: +1.50 DS and OS:-2.00 DS. Although both patients will have good monocular corrected acuities, they will most likely possess poor stereopsis due to a decreased amount of binocular neurons because the eyes are never in focus at the same distance.

It is important to note that in order for amblyopia to occur, ametropia must be present during the critical period.

What is the equivalent of a Reduced Snellen 20/50 optotype in metric notation (assuming a working distance of 40 cm)?
2M
1M
0.5M
0.67M

To convert from Reduced Snellen to metric notation one must divide the denominator by 50. In the above example 50/50 = 1M.

To convert from Reduced Snellen to Printer's point, divide the denominator by 6. To convert from Printer's point to metric, divide by 8. To convert from Metric notation to Reduced Snellen, multiply by 50; this will give you the denominator of Reduced Snellen.

A good rule of thumb is 1M = RS 20/50 = 8 point.

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What is the Interval of Sturm for a spherocylindrical lens with a power of +6.00 -2.00 x 090?
20 cm
16.7 cm
41.7 cm
8.3 cm
25 cm

The powers in each meridian of the lens are +6.00 and +4.00.
The Interval of Sturm is simply the distance between the focal point of each power.

1/+6.00 = 16.7cm
1/+4.00 = 25.0cm

25cm - 16.7cm = 8.3cm

What is the minimum thickness necessary for an antireflective coating (n=1.9) to be useful against incident light of 530 nm wavelength?
58.3 nm
69.7 nm
139.5 nm
132.5 nm
278.9 nm

The equation for finding the minimum antireflective coating thickness is:

thickness = wavelength/(4 x index of coating)
thickness = 530 / (4 x 1.9)
thickness = 530 / 7.6
thickness = 69.73 nm

What separation distance will make the combination of a +3.00 and a +10.00 thin lens afocal?
23 cm
0.43 cm
2.3 cm
43 cm
1.7 cm
17 cm

For this question, the equation for equivalent power of a thick lens system should be used, solving for thickness (t).

De = D1 + D2 - (t/n) x D1D2
De = equivalent power, D1 = front surface power, D2 = back surface power
t = thickness of lens system, n = index between the 2 surfaces

An afocal system has its focal points (F and F') located at infinity. Therefore, an incident parallel pencil of light rays will emerge into image space as a parallel pencil as well. Another way to characterize an afocal system is that the equivalent power (De) is 0.

In the above question, De = 0, D1 = +3.00, D2 = +10.00, n= 1
0 = 3 + 10 - ((t/1) x (3) x (10))
0 = 13 - (t x 3 x 10)
0 = 13 -30t
30t = 13
t = 0.43 m (or 43 cm)

If the two lenses are separated by 43 cm, the lens system can be considered afocal. This type of combination of two plus lenses is also an example of a simple astronomical (Keplerian) telescope. Keep in mind that the image in this type of optical system is inverted.

Which of the following BEST describes the definition of irregular astigmatism?
The principal meridians of the cornea are located 90 degrees apart
The principal meridians of the cornea are not perpendicular to each other
The axis of astigmatism is located along an oblique axis
The axis of astigmatism is located along the 90 degree meridian

Astigmatism can be classified as either being regular or irregular. Regular astigmatism occurs in individuals in which the principal meridians of the cornea are located 90 degrees apart. That is, the area of the cornea with the flattest curvature (the axis) is oriented perpendicular to the meridian of the steepest curvature.

In certain ocular conditions such as keratoconus, corneal scarring, or post-surgical corneas, the steep and flat meridians may not be oriented 90 degrees apart. This type of corneal curvature can be considered irregular astigmatism. In these cases, the refractive error is typically not well corrected with spectacles, in comparison to correction with gas-permeable contact lenses.

Which type of light scattering is responsible for the reddish-orange colors that are often observed during sunsets?
Mie scattering
Brillouin scattering
Rayleigh scattering
Raman scattering
Tyndall scattering

Scattering of light occurs when the medium through which light or other electromagnetic radiation travels is not homogenous. In the case of Rayleigh scattering, the particles that scatter the light are smaller than the wavelength of the light passing through. The particles may be individual atoms or molecules of a solid, liquid, or most commonly, a gas. The appearance of the blue sky during the day and the reddish hue of the sunset are due to Rayleigh scattering of light.

While performing the astigmatic clock dial, your patient reports that the clearest/blackest line is the 2-8 line while the 5-11 line is the least clear. What would be the corresponding axis of astigmatism?
60 degrees
30 degrees
180 degrees
150 degrees

In order to determine the corresponding axis of astigmatism utilizing the clock dial, one must multiply the smallest number of the clearest clock position by 30 degrees. In our case 2 x 30= 60 degrees. In general the line perpendicular to the clearest line is generally the least clear as this corresponds to the second principal meridian of the eye. Remember the principal meridians of the eye are 90 degrees apart.

What is the net overall moles of ATP produced by the electron transport chain (i.e. not including glycolysis)?
2 moles of ATP
30 moles of ATP
34 moles of ATP
6 moles of ATP
38 moles of ATP

The electron transport chain yields a total of 34 moles of ATP. Glycolysis produces a total of 2 moles of ATP. The overall net of cellular respiration is 36 moles of ATP.

Which of the following is a precursor to steroid hormones such as testosterone?
Phospholipids
Triglycerides
Sphingolipids
Cholesterol

Progesterone, aldosterone, testosterone, estradiol and cortisol are all derived from cholesterol. Cholesterol has a unique configuration comprised of four joined cycloalkane rings. Because these hormones are fat-soluble, they readily pass through cell membranes. They diffuse into the blood and are generally bound to carrier proteins, which transport the hormones to their designated target site where they may further undergo processing or transformation.

Sphingolipids are important in cell membranes, especially those located in the central nervous system, such as myelin sheath. Sphingolipids contain sphingosine as a backbone and are then further classified depending on which molecules are attached to that backbone, such as ceremides, gangliosides, sphingomyelin, etc.

Phospholipids contain a polar and non-polar end, thus making them amphoteric. This property allows for the formation of bilayers (polar ends aligned together and pointed outwards) resulting in the lipid bilayer commonly seen in cell membranes. Phospholipids are generally comprised of a phosphate group, a choline group (polar), and two fatty acid chains (non-polar) attached to glycerol, which serves as the backbone.

Triglycerides are comprised of three fatty acid chains attached to a glycerol backbone. Triglycerides are important in long-term energy storage for use by cells.

What is the name of the pigmented line that represents the leading edge of a pterygium?
Fleischer's ring
Krukenberg's line
Stocker's line
Hudson-Stahli line
Coat's white ring
Ferry's line

- Stocker's line is a deposition of iron in the corneal epithelium that is located at the leading edge of a pterygium
- A Hudson-Stahli line is an iron line that is commonly observed at the junction of the middle and lower third of the cornea (where lid closure occurs upon blinking)
- Ferry's line is found in front of a filtering bleb
- Coat's white ring is a small, white, oval ring at the level of Bowman's membrane that is associated with a previous corneal foreign body
- A Fleischer ring is an iron pigment that encircles the base of a cone in keratoconus
- A Krukenberg spindle is a deposition of pigment on the corneal endothelium that is associated with pigment dispersion syndrome

What is the name of the surgical procedure in which thermal laser burns are placed in the mid-periphery of the cornea in an attempt to steepen the corneal curvature?
Limbal relaxation incisions
Laser-assisted in-situ keratomileusis
Radial keratotomy
Photorefractive keratectomy
Conductive keratoplasty

In cases where the corneal curvature must be steepened in order to correct for refractive error (hyperopia or presbyopia), conductive keratoplasty (CK) is a viable surgical option. Although this surgical procedure was used more often in earlier years, it is not currently as widely used as laser-assisted in-situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). In comparison to CK, LASIK and PRK tend to be safe, have long-standing results, and more predictable outcomes. The CK technique involves using a radiofrequency probe to create burns in either one or two concentric rings in the mid-peripheral region of the cornea. These thermal laser burns cause subsequent stromal shrinkage, which results in an increase in the curvature of the cornea. This change in curvature typically decays over time, but the procedure can be repeated.

Radial keratotomy is also an older surgical procedure in which a diamond blade is used to create several radial corneal incisions (the number and depth of the incisions depends on the refractive error) in order to flatten the corneal curvature in patients with myopic refractive errors. Limbal relaxation incisions are similar in that arcuate incisions are made on opposite sides of the corneal periphery in the meridian of the "plus" cylinder axis in order to create flattening of the steep corneal curvature (with some smaller steepening of the flat meridian) in an attempt to reduce the amount of corneal astigmatism.

Photorefractive keratotomy (PRK) and laser-assisted in-situ keratomileusis (LASIK) are refractive surgery techniques that use an excimer laser to ablate corneal tissue to a certain depth in either the central cornea (to correct myopia) or peripherally (to correct hyperopia).

Which layer of the cornea, if penetrated, will leave a scar?
The tear film
The epithelium
The wing cell layer
The stroma

The corneal epithelium is comprised of 3 major layers. The outermost layer is composed of superficial cells (2-3 layers) followed by wing cells (2-3 layers) and, lastly, basal cells (1 layer). Damage to the epithelium will heal without keloid formation. The epithelial basement membrane is made up of collagen types IV, VII and XII.

The stroma makes up the bulk of the cornea and is comprised of keratocytes, nerves, type I collagen fibers and mucopolysaccharides. If injured, the stroma will heal but a scar will remain at the site of trauma.

The tear film lies anterior to the cornea and is not composed of tissue and as such cannot scar, nor is it considered a part of the cornea.

Which of the following ocular signs is virtually pathognomonic for trachoma caused by chlamydia?
Lymphadenopathy
Superior tarsal follicles
Inferior tarsal papillae
Tranta's dots

Chlamydia causes two forms of conjunctivitis, trachoma and inclusion. Trachoma is more common in lesser-developed countries and can cause blindness if not treated appropriately. Trachoma presents in several stages, initially starting with mucopurulent discharge, lymphadenopathy, red eye, small superior tarsal follicles, and mild superior pannus. As the condition evolves, the formation of limbal follicles occurs and will eventually scar causing Hebert's pits, which are characteristic of this infection. This condition, if left untreated, ultimately progresses to horrible scarring of the eyelid (Arlt's line) and cornea, causing extremely poor visual acuity. Diagnosis is made with the observation of two or more of the following: follicles on the upper tarsus, pannus (particularly superiorly), limbal follicles or Herbert's pits and typical conjunctival scarring of the upper lid. Treatment includes oral doxycycline, tetracycline, or erythromycin along with topical tetracycline or erythromycin ointment. Azithromycin is also a good choice because it is given as 1000 mg PO which delivers exceptional compliance; however, this is not to be prescribed to those with liver disease or to young adults under the age of 16.

Inclusion conjunctivitis is linked to venereal disease and can present either unilaterally or bilaterally (which is more common) as follicles on the upper and lower tarsal plates (lower follicles will be larger and more prominent), lymphadenopathy, possible mucopurulent discharge, lid edema, micropannus, superior corneal sub-epithelial infiltrates, superficial punctate keratitis, and scarring of the upper eyelid (sometimes called Arlt's line or "basketweave" because of its appearance). This type of conjunctivitis is less severe than trachoma. Treatment is similar to that of trachoma.

Follicles are related to cellular immunity which serves to protect against viruses. Many types of viral infections can cause inferior palpebral follicles, such as EKC, Herpes simplex and molluscum contagiosum. Superior tarsal follicles are highly suggestive of a chlamydial infection. A superior papillary response is generally associated with an allergic response. Inferior tarsal papillae are frequently seen in bacterial infections and allergic responses as papillae act as the release sites for both eosinophils (associated with allergies) and polymorphonuclear leukocytes which destroy bacteria.

References:
Clinical Ophthalmology, A Systematic Approach 5th edition. Kanski, J. Butterworth-Heinemann, Elsevier Science, 2003, pages 70-73.

Vaughan & Ashbury's General Ophthalmology 16th edition, Riordan-Eva, P., Vaughan, D. & Asbury T., McGraw-Hill, 2004, pages 105-108.

Which of the following alterations will help to loosen a tightly-fitting gas-permeable lens?
Steepen the base curve of the lens
Increase the overall diameter
Steepen the peripheral curve system
Reduce the width of the peripheral curve system
Reduce the size of the optic zone

There are a multitude of alterations that can be made when a lens is fitting too tightly, many of which can be done in-office if a modification unit is available. If a gas-permeable lens is fit too tightly, the most commonly altered parameter is flattening of the base curve. One can also decrease the optic zone, decrease the overall diameter (OAD), widen the peripheral curve system, or flatten the peripheral curve system. In order to modify a lens that is fitting too loosely, simply reverse all of the above: steepen the base curve, increase the OAD, increase the optic zone, steepen the peripheral curve system, and narrow the width of the peripheral curves.

Which of the following will occur if you increase the water content of a soft hydrogel contact lens?
The patient will report an increase in dry eye symptoms
The tendency of lens deposits will decrease
The oxygen permeability will decrease
The lens durability will increase

As the water content of a soft hydrogel contact lens increases, generally the durability of the lens will decrease, the permeability of the lens will increase as will deposit formation and dry eye symptoms.
This is also mostly try for silicone-hydrogel lenses, except for the fact that with these lenses, as water content increases, the permeability of the lens tends to decrease.

Which one of the following bitoric GP contact lenses would NOT induce cylinder if rotated to a misaligned position on the eye?
7.54 mm / +1.50 D --------------------- 7.99 mm / +2.75 D
7.63 mm / -1.50 D --------------------- 8.11 mm / +1.12 D
7.46 mm / -4.25 D --------------------- 8.13 mm / -1.75 D
All of the options listed would induce cylinder if rotated off axis
7.58 mm / -5.37 D --------------------- 8.18 mm / -0.50 D

Cylinder power effect (CPE) bitoric and base curve toric (with a spherical front-surface) gas-permeable (GP) lenses will induce unwanted cylinder if the lens rotates off axis. The resulting cylinder is due to cross-cylinder effects. However, a spherical power effect (bitoric) will not induce unwanted cylinder regardless of lens rotation. To determine whether a GP lens is a spherical power effect (SPE) or cylinder power effect (CPE) bitoric, measure the two base curves using a radiuscope and the two raw contact lens powers using a lensometer. If the difference between the two base curve meridians in diopters is the same as the difference between the two raw powers, the lens is an SPE bitoric. This is the case for only one of the above answers. Converting mm of base curve radius to diopters results in 7.63 mm = 44.25 D and 8.11 mm = 41.62; a difference of 2.62 D. The difference between the two raw powers of +1.12 D and -1.50 D is also 2.62 D. Therefore, this lens is a spherical power effect (SPE) bitoric GP contact lens.

You are fitting a toric soft contact lens to your patient's right eye. The patient's manifest refraction is -2.00 -1.50 X 095. You apply a -1.75 -1.25 X 085 diagnostic toric soft contact lens. It fits well, and the prism base down marking consistently locates halfway between the 6 o'clock and 7 o'clock hours. What axis should you order?
70 degrees
80 degrees
110 degrees
95 degrees
100 degrees

Applying LARS to compensate for lens rotation, since the lens is rotated to the Left, you would Add the amount of left rotation to the manifest refraction axis. Every hour on the clock dial would translate to 30 degrees rotation. In the above example, the lens is rotated to the doctor's left by 15 degrees (between the 6 and 7 o'clock hours). Add the amount of rotation (15 degrees) to the cylinder axis of the manifest refraction (95 degrees). This results in a cylinder axis order of 110 degrees.

Which of the following correctly describes the autonomic innervation of the iris muscles?
The iris sphincter is innervated sympathetically and the iris dilator is innervated parasympathetically
The iris sphincter and iris dilator are both innervated sympathetically
The iris sphincter and iris dilator are both innervated parasympathetically
The iris sphincter is innervated parasympathetically and the iris dilator is innervated sympathetically

Stimulation of the sympathetic nervous system results in pupil dilation and the parasympathetic nervous system pupil constriction. Accordingly, the sphincter muscle (which constricts the pupil) is innervated by the parasympathetic nervous system and the dilator muscle (which dilates the pupil) is innervated by the sympathetic nervous system.

Ref: Remington, LA. Clinical Anatomy of the Visual System, 1998 p 44

Which of the following types of scleritis presents without ocular inflammation, has a low risk for perforation, and does not typically result in pain or decreased visual acuity?
Granulomatous necrotizing scleritis
Scleromalacia perforans
Posterior scleritis
Vaso-occlusive necrotizing scleritis
Nodular scleritis
Anterior non-necrotizing diffuse scleritis

Scleromalacia perforans is a type of necrotizing scleritis that typically presents without vascular congestion or pain. Clinical observations commonly include yellow-colored necrotic plaques that occur near the limbus without inflammation and very slow progression of scleral thinning that eventually exposes the underlying uveal tissue. Patients commonly complain of a mild non-specific irritation but no pain. Visual acuity is also not usually affected in these patients. Scleromalacia perforans typically affects elderly women with a long-standing history of rheumatoid arthritis. By the time patients are correctly diagnosed with this condition, treatment is usually not needed or is ineffective. Even though the name contains the word "perforans," the risk of perforation is extremely rare, as the integrity of the globe is usually well maintained.

Which type of anterior scleritis is associated with the highest risk of perforation?
Diffuse
Necrotizing
Nodular
Scleromalacia perforans

Scleritis is an inflammation of the sclera that generally occurs secondarily to a systemic condition, usually of collagen vascular origin. Diffuse scleritis has a gradual onset and presents as a boring pain which may radiate to other structures such as the jaw and forehead. Patients will present with distension of the scleral vascular pattern, causing a deep pinkish hue of the sclera. Nodular scleritis appears similar to diffuse scleritis, but the areas of inflammation are localized to painful, raised nodules. Scleromalacia perforans is the least common form and is almost always seen in association with rheumatoid arthritis. Patients with scleromalacia perforans generally do not experience pain or inflammation. Necrotizing scleritis is the most severe form and has a higher mortality rate than the other types due to the fact that it usually stems from autoimmune diseases.

References: Schwartz, G. Around the eye in 365 days (2009) page 314.

Pavan-Langston, D. Manual of Ocular Diagnosis and Therapy, 6th edition (2008) pp 133-136.

Which of the following drugs decrease intraocular pressure by increasing uveoscleral outflow?
Pilocarpine
Brinzolamide
Timolol
Brimonidine
Dorzolamide

Glaucoma medications lower intraocular pressure by either decreasing aqueous production or by increasing aqueous outflow. There are three classes of drugs for which the mechanism of action is increasing aqueous outflow: cholinergic agonists, prostaglandin analogs, and alpha-2 agonists. Cholinergic agonists, such as pilocarpine, work by increasing trabecular outflow, whereas prostaglandin analogs and alpha-2 agonists work by increasing uveoscleral outflow. The other classes of glaucoma medications, such as beta-blockers and carbonic anhydrase inhibitors, work by decreasing aqueous production.

It is important to note that alpha-2 agonists, such as Brimonidine (Alphagan®) and Apraclonidine (Iopidine®), have dual mechanisms of action. This class of medication decreases intraocular pressure by both increasing uveoscleral outflow and decreasing aqueous production.

When examining a patient, a pinpoint spot of the posterior surface of the lens known as Mittendorf's dot is seen. What is this a remnant of?
Pupillary membrane
Hyaloid artery
Glial tissue of the optic nerve
Vitreous

Mittendorf's dot is a remnant of the hyaloid artery and appears as a black dot on the posterior surface of the lens. Pupillary membrane remnants would be present in front of the lens and are a complex of fibers. Glial tissue of the optic nerve head is a remnant that is known as Bergmeister's papilla.

Ref: Remington, LA. Clinical Anatomy of the Visual System, 1998 pp 110

Which of the following types of congenital cataracts are characteristic of galactosemia?
Christmas tree cataracts
Blue dot (Cerulean) opacities
Oil droplet opacities
Sunflower cataracts

Central oil droplet opacities are a type of congenital cataract that is associated with galactosemia, a genetic metabolic disorder that affects the body's ability to metabolize galactose properly.

Blue dot (Cerulean) opacities are congenital cataracts and are not usually associated with systemic disease but are thought to be due to autosomal dominant mutations in several genes.

Christmas tree cataracts are not considered a congenital type of cataract; they are a rare variant of senile cataracts that have a strong association with myotonic dystrophy.

Sunflower cataracts are also not considered congenital cataracts and are due to the abnormal deposition of copper in patients suffering from Wilson's disease.

You are measuring the palpebral fissure height in a patient reporting drooping of his upper eyelid. Which of the following BEST describes the normal positioning of the upper and lower eyelids in comparison to the limbus?
The upper lid normally rests about 2mm lower than the upper limbus, and the lower lid rests about 1mm lower than the lower limbus
The upper lid normally rests about 2mm lower than the upper limbus, and the lower lid rests about 1mm above the lower limbus
The upper lid normally rests about 1mm lower than the upper limbus, and the lower lid rests about 2mm above the lower limbus
The upper lid normally rests about 1mm lower than the upper limbus, and the lower lid rests about 2mm lower than the lower limbus

The palpebral fissure height is a measurement of the distance between the upper and lower eyelid margins when the patient is looking in primary gaze. This particular measurement is typically less in males (7-10mm) as compared to females (8-12mm). The normal positioning of the upper and lower eyelids are as follows: the upper eyelid usually rests about 2mm below the superior limbus, while the lower eyelid position is typically 1mm above the lower limbus. A unilateral ptosis can be quantified by comparing these measurements to the contralateral eye. A ptosis up to 2mm may be graded as mild; a 3mm ptosis is considered moderate; a ptosis of 4mm or more is deemed severe.

Another important measurement in evaluating a ptosis is the marginal-reflex distance (MRD). The MRD can be defined as the distance between the upper eyelid margin and the resultant corneal reflection caused by directing a patient's gaze at a penlight held by the examiner. This measurement is normally 4-4.5mm.

Which of the following is the correct pathway for the drainage of tears through the nasolacrimal drainage system?
Nasolacrimal duct, lacrimal sac, valve of Hasner, lacrimal canaliculus, ampulla, lacrimal punctum
Lacrimal punctum, lacrimal canaliculus, ampulla, lacrimal sac, nasolacrimal duct, valve of Hasner
Lacrimal sac, lacrimal punctum, lacrimal canaliculus, ampulla, nasolacrimal duct, valve of Hasner
Lacrimal punctum, lacrimal canaliculus, ampulla, valve of Hasner, nasolacrimal duct, lacrimal sac

The lacrimal punctum is a small aperture located in the lacrimal papilla, the slight elevation at the junction of the lacrimal and ciliary portions of the eyelid margin. Initially, the tear film drains through this aperture. The lacrimal punctum leads into the lacrimal canaliculus, the tube connecting the punctum to the lacrimal sac. The ampulla is a slight dilation in the initial portion of the lacrimal canaliculus. The canaliculi from the upper and lower lids run horizontally along the lid margin, connecting into a common canaliculus that then enters the lateral aspect of the lacrimal sac located in the anterior portion of the medial orbital wall. The lacrimal sac empties into the nasolacrimal duct in the maxillary bone. The valve of Hasner is located at the terminus of the nasolacrimal duct in the inferior nasal meatus. The Valve of Hasner is a fold of mucosal tissue that ensures that fluid flows anterograde out of the duct.

Ref: Remington, LA. Clinical Anatomy of the Visual System, 1998 pp 153-154

Which of the following skin conditions is considered to be benign and has the LOWEST risk of malignancy?
Squamous cell carcinoma
Keratoacanthoma
Actinic keratosis
Basal cell carcinoma

Keratoacanthoma appears very much like squamous cell carcinoma (SCC) in that it tends to progress rapidly and appears to ulcerate. This condition typically occurs in middle-aged and elderly patients of Caucasian descent on areas of the skin that are exposed. The lesion appears elevated, and eventually the center will produce a scab-like plug of keratin. The margins surrounding the plug will be rolled. At some point the keratin plug will fall out, resulting in the formation of a pit, and the lesion will regress. Most patients and clinicians do not like to wait this condition out due to its similarities to SCC.

Actinic keratosis is a pre-cursor to squamous cell carcinoma and appears as scaly, dry skin that does not heal. People with skin that is of lighter pigmentation along with excessive exposure to ultraviolet light tend to be most at risk for development of this condition.

Squamous cell carcinoma (SSC) is thankfully one of the rarest malignancies but due to its ability to metastasize can be quite dangerous. This malignancy has the ability to progress rapidly and has a high affinity for people who spend a lot of time in the sun, especially those who are light-skinned. The only way to definitively diagnose SCC is to refer for a biopsy and ensuring the use of Mohs technique. This strategy takes more time but ensures that the lesion is removed. Essentially, Mohs procedure calls for removal of tissue and biopsy of the surrounding borders. If the borders prove to be malignant then more tissue is removed and biopsied. This continues until the borders prove to be free of any carcinoma.

Basal cell carcinoma (BCC) is the most common malignant lid lesion and mercifully tends to be very slow-growing. BCC generally appears as a waxy, translucent nodule. Eventually the nodule will ulcerate. Patients may bring these to your attention and tell you that they have "had it for years and it just does not seem to heal". Whenever you hear this it is best to send out for biopsy via Mohs technique. BCC very rarely metastasizes.

Which patient would be considered legally blind?
A wet macular degeneration patient with best central acuities of 10/120 OD and 10/200 OS
A patient with a total retinal detachment of the right eye, no light perception and a best corrected central acuity of 8/60 due to wet macular degeneration
A patient with Best's disease with best corrected central acuities measure OD 10/80 and OS 10/100
A myopic patient with acuities of 20/400 OD and OS uncorrected
A retinitis pigmentosa patient who has 20/20 central vision in each eye and a 30 degree in diameter visual field

Legal blindness must take into account central best corrected visual acuity, with the better eye 20/200 or worse. If the central acuity is normal such as in the RP patient then the field would be the restricting qualification, which, at 30 degrees, does not qualify.

What term describes the phenomenon in which a bacterium directs its movement TOWARD a chemical in its environment?
Apoptosis
Transposition
Chemotaxis
Phagocytosis

Many bacteria possess flagella, or thread-like appendages, which allow for movement. Certain chemicals attract bacteria (chemoattractants), while others repel them (chemorepellents). Chemotaxis refers to the response of the bacteria to either chemoattractants or chemorepellents. In the absence of either of the aforementioned chemicals, bacteria will move in random patterns. Some bacteria possess genes and proteins which allow for the sensing of concentration gradients in their environment. In the presence of a chemoattractant, bacteria will have longer runs in the appropriate direction.

Apoptosis is defined as programmed cell death.

Phagocytosis refers to the engulfment of a particle (for example, bacteria) by a phagocyte (for example, a macrophage).

Transposition refers to the rare phenomenon in which genes move from one place on the genome to another position.