Ophthalmology Exam

What are the three tunics of the eye?

Fibrous (most outer, sclera/cornea)

Vascular (iris, ciliary body, choroid)

Neurosensory (retina)

What are the three fluid-filled chambers of the eye?

Anterior chamber (filled w/ aq humor)

Posterior chamber (filled w/ aq humor)

Vitreal chamber (filled w/ vitreous humor)

What is the function of the cornea?

Refracts/bends light entering the eye (more powerful than the lens, like the gross focus of a microsope). Also protects interior structures from injury/infection.

What is the function of the lens?

Accommodates/changes shape to focus light into the back of the eye

What is phototransduction?

Receptors in the eye are stimulated by light, creating electrical signals

Ganglion cell axons of the retina aggregate to become the ____?

Optic nerve

What is the function of the optic nerve?

Gathers electrical signals from the retina and carries them to the brain.

What parts make up the fibrous tunic?

Cornea, limbus, and sclera

What is the limbus?

The circular border between the cornea and sclera.

It is important that the fluid of the eye is what color to allow for clear vision?

Clear

The outermost epithelium of the cornea does what?

Constantly replaces cells

The stroma of the cornea is made up of what? It makes up about 90% of the thickness of the cornea.

Collagen

What is descemet’s membrane?

Basement membrane of endothelium in the cornea. It thickens with age.

What is the function of the innermost endothelium of the cornea?

Pulls fluid out of the stroma to return it to aqueous humor.

What are the three cell types described in the corneal epithelium?

Superficial cells (slough continuously)

Wing cells (differentiated basal cells)

Basal cells (attached to stroma)

What is the source of new collagen in the corneal stroma?

Keratocytes

If the collagen fibers of the corneal stroma were irregular, what would be the consequence?

Light wouldn’t be able to pass through as well, causing the vision to be compromised

The corneal stroma is largely _____.

AcellularW

What types of collagen exist in the corneal stroma?

I, III, V, VI, and XII

What are some of the proteoglycans and glycosaminoglycans found in the corneal stroma?

Keratan sulfate

Chondroitin sulfate

Heparan sulfates

Hyaluronans

Describe the structure of the corneal endothelium.

Monolayer of hexagonal cells.

The loss of cells in the corneal endothelium causes what condition?

Corneal edema (fluid build-up in the cornea)

What is the point of corneal decompensation?

The fluid in the cornea is accumulating more quickly than what can be removed.

What collagen types make up descemet’s membrane?

Types III, IV, V, VI, and VIII

The corneal innervation branches from what nerve?

Trigeminal nerve (cranial nerve V)

The corneal innervation is most concentrated where? What advantage does this provide?

Superficially (anteriorly), allows for better reaction time to corneal irritation/damage.

What characteristics contribute to corneal clarity?

Avasularity

Anhydrous (relatively dehydrated)

Absense of pigment

Non-keratinized anterior epithelium

Regular arrangement and small size of stromal collagen fibrils

What are corneal ulcers?

Loss of some of the layers of the eye. AKA corneal perforation.

Where is the source of stem cells for epithelial regeneration of the cornea?

The limbus

What is the sclera made of?

Collagen and elastin

What passes through the sclera on the way to innervate the remainder of the eye?

Blood vessels and nerves

Describe the tissue arrangement of the sclera?

Dense, irregular connective tissue. Collagen fibrils are irregular in size and orientation.

What is the innermost margin of the sclera?

Lamina fusca

What is the loose exterior connective tissue of the sclera called?

Episclera

Where can you find dermatan sulfate laden proteoglycans?

The sclera

In non-mammals, what structure is sometimes present as support wthin the sclera?

Bony or cartilaginous ossicles

What is the lamina cribrosa?

The “sieve” through which retinal ganglion cell axons exit the globe and coalesce into the optic nerve.

What is the ocular adnexa?

The supporting structures and tissues of the eye

What is the orbit?

Bony protection for the globe (eye)

What bones typically make up the orbit? Hint: FLMPS

Frontal, lacrimal, maxillary, palatine, and sphenoid bones

In what types of animals is the bony orbital usually complete? What about incomplete?

Complete: herbivores

Incomplete: carnivores

The location of orbits in the skull determines in part what?

Degree of binocular vision

The orbit contains what? (Try to name a few structures)

Globe

Optic nerve

Extraocular muscles

Lacrimal gland

Third eyelid

Masticatory and pterygoid muscles

Adipose tissue

Fascial sheaths (orbital fascia)

What are the three orbital fascia?

Periorbita (periosteum)

Tenon’s capsule

Fascial sheaths of the extraocular muscles

What are the three muscle groupings of the extraocular muscles?

Rectus muscles

Oblique muscles

Retractor bulbi

What are the four parts of the rectus muscles?

Lateral

Medial

Dorsal

Ventral

What are the two parts of the oblique muscles?

Superior (dorsal)

Ventral

What are the functions of the eyelids?

Protect globe

Distribute tear film

Pump spent tears into nasolacrimal apparatus

Help control amount of light entering the eye

What is the purpose of the orbicularis oculi muscle?

Close the eyelid

What are cilia in the context of the eyelid?

Eyelashes

What glands lie within the eyelid, producing the lipid part of tears?

Meibomian glands

What are the four muscles of the eyelid?

Orbicularis oculi

Levator palpebrae superioris

Muller’s muscle

Retractor anguli oculi

Which muscle closes the palpebral fissue?

Orbicularis oculi

Which muscles raise the upper lid?

Levator palpebrae superioris, Muller’s muscle

What muscle supports and keeps the lateral canthus of the eyelid extended?

Retractor anguli oculi

What are the biggest concerns with eyelid trauma?

Major concern is globe exposure

Should be repaired promptly

Margins should be preserved

Eyelashes (cilia) are absent in what species?

Cats

What is the function of the eyelashes (cilia)?

Protection and surveillance

What is the condition called when eyelashes (cilia) increase in length or thickness?

Trichomegaly

In avian species, the cilia are modified feathers called ___?

Filoplumes

What is distichiasis?

When eyelashes grow through meibomian glands and irritate the eyes.

What is the spectacle in snakes?

Fused, transparent eyelids that shed concurrently with their skin

What is the conjunctiva of the eye?

MucoWsal lining associated with the eye/eyelids.

What are the three regions of the conjunctiva?

Palpebral, fornix, and bulbar

What are the functions of the conjunctiva?

Produces mucin component of tear film

Immune surveillance

What is conjunctivitis?

Inflammation of the conjunctiva

Non-specific clinical finding, could be due to a lot of things

Hypermia (redness), chemosis (swelling)

What is the nictitans/nictitating membrane?

The third eyelid

What is the third eyelid?

Semilunar fold of conjunctiva surrounding a T-shaped cartilaginous support

What is the purpose of the third eyelid?

Protect the globe, produce and distribute tears

Who has more control over the third eyelid: mammalians or non-mammalians?

Non-mammalians

What is the prolapse of the third eyelid gland also called?

Cherry eye

What could happen when prolapse of the third eyelid gland is not corrected?

Inflammation and loss of function

What is the purpose of the nasolacrimal system?

Secretory: Orbital lacrimal gland, gland of third eyelid, meibomian glands, conjunctival goblet cells

Drainage: through puncta at medial canthus, lacrimal sac/duct, and nasal puncta

What are the functions of tears?

Cleans/lubricate the ocular surface

Provide nutrition and O2 (instead of blood vessels, which would compromise vision)

Antimicrobial defense

Maintains optically uniform surface

What produces the aqueous, lipid, and mucin components of tears?

Aq - Lacrimal glands

Lipid - Meibomian glands

Mucin - Conjunctival goblet cells

What is keratoconjunctivitis sicca?

Dry eye:

Quantitative deficiency of aqueous tears. Causes ocular irritation/discomfort, compensatory mucoid discharge.

What is epiphora?

Increased tear production or decreased tear drainage

What is a dacryocystorhinography?

Contrast study to determine function of nasolacrimal ducts

What is the ocular fundus? What is contained in it?

The back of the eye: Retina, tapetum, choroid (including blood vessels), optic disk

What is the function of the retina?

Transformation of light energy (photons) into electrical signals

The retina is known for being the most ____ ____ tissue in the body.

Metabolically active

Why is retinal detachment such an emergency?

Because of its very high metabolic needs, it must be in constant contact with the choroid.

The photoreceptor layer of the retina is made of what structures (allows us to discern light and colors)?

rods and cones

What does the tapetum allow for?

A “second chance” for light absorbance after it’s passed through the retina. Light passes through from the front, bounces off the tapetum, and passes again through the back side of the retina.

What lies between the photoreceptor layer of the retina and the choroid?

The retinal pigmented epithelium

Most domestic animal species are __-chromats.

Dichromats! (Humans are trichromats)

Explain the difference between humans and dogs/cats in their rod and cone concentrations.

Dogs and cats have more rod-dominated retinas, allowing for better vision in dim light and better perception of movement. Humans can see more colors.

Explain how light energy becomes a nervous impulse.

Light is absorbed by photopigments in rods and cones, whose chemical rxns cause changes in neurotransmitter release. Bipolar cells respond, who are then responded to by ganglion cells. The ganglion cell axons send an impulse down their lines to the optic nerve, which eventually reaches the brain.

The optic nerve is supported by what types of neural cells?

Astrocytes and oligodendrocytes

What is the optic disc in the retina?

The end of the optic nerve. It is the only part of the CNS that is visible to an examiner.

What is the optic chiasm?

Information from both eyes is exchanged at the chiasm, allowing for information from both eyes to reach both halves of the brain.

What artery feeds the eye?

Internal maxillary

What percentage of ocular blood flow goes to the retina and the choroid?

Retina: 4%

Choroid: 85%

What are the four patterns of retinal vasculature?

Holangiotic (fewer large branches that emerge from optic disc)

Paurangiotic (diffuse, small branches from the optic disc)

Merangiotic (pairs of vessels extend horizontally ONLY, seen in rabbits)

Anangiotic (no retinal blood vessels. usually seen in exotics)

What are a few examples of an extraretinal blood supply?

Pecten, conus papillaris, choroidal papillae

What helps determine the visual field of an animal?

Are they a predator or prey animal?

Position of orbit relative to midline

Pupil size/shape

What is visual acuity?

The sharpness of an image

What adaptations help animals see in dim light?

Large relative proportion of rods

Tapetum

Pupil shape/size

Most mammals are dichromats. They usually do not perceive what color?

Red

Domestic animals often cannot see as many colors as humans. What do their eyes see better than ours?

Flicker detection/motion, larger visual fields, superior night vision