N335 Chapter 15 Eye Assessment Study Guide

Learning Objectives for Eye Assessment

• Identify the external anatomic features of the eye.

• Describe the internal anatomy of the eye.

• Identify the structures viewed through the ophthalmoscope and compare/contrast versus abnormal findings.

• Define pupillary light reflex, fixation, and accommodation.

• Describe ways to test visual acuity and extra ocular muscle strength and discuss the meaning of abnormal findings.

• Identify age-related changes in the eye for older adults and developmental concerns for infants and children.

• Discuss the three most common causes of decreased visual functioning in the older adult.

• Incorporate health promotion concepts when performing an assessment of eyes.

External Anatomy of the Eye

• Bony Orbital Cavity: The eye is situated within this cavity, which is surrounded by a cushion of fat to provide protection for the globe.

• Palpebral Fissure: This refers to the elliptical open space between the eyelids.

• Limbus: The border or junction located between the cornea and the sclera. Medial and lateral.

• Canthus: The corner of the eye, which is the angle where the eyelids meet. There is a medial (inner) and lateral (outer) canthus.

• Tarsal Plates: These are strips of connective tissue within the upper lid that give it shape and containing the meibomian glands.

  • Meibomian Glands: Modified sebaceous glands located in the tarsal plates that secrete an oily lubricating material onto the lids to prevent tears from overflowing and create an airtight seal when eyes are closed.

• Conjunctiva: A thin mucous membrane folded like an envelope between the eyelids and the eyeball. Lubricates eye, secretes mucous and tears. Protective layer.

• Cornea: A thin, transparent, and very sensitive structure that covers the iris and pupil.

• Lacrimal Apparatus: This system provides constant irrigation to keep the conjunctiva and cornea moist and lubricated.

  • Lacrimal glands excrete tears.

• Extraocular Muscles (EOM): There are six muscles that attach the eyeball to its orbit and serve to direct the eye to points of interest. These are innervated by three cranial nerves ($CN$): Holds eye symmetrical and helps eyes move at same time.     

  • Superior Rectus: Innervated by Cranial Nerve $III$ (Oculomotor Nerve).     

  • Inferior Rectus: Innervated by Cranial Nerve $III$ (Oculomotor Nerve).     

  • Lateral Rectus: Innervated by Cranial Nerve $VI$ (Abducens Nerve).     

  • Medial Rectus: Innervated by Cranial Nerve $III$ (Oculomotor Nerve).     

  • Superior Oblique: Innervated by Cranial Nerve $IV$ (Trochlear Nerve).     

  • Inferior Oblique: Innervated by Cranial Nerve $III$ (Oculomotor Nerve).

Internal Anatomy of the Eye

The eye is a sphere composed of three concentric coats:

• Outer Fibrous Sclera:     

  • Sclera: A tough, protective, white covering. Very limited blood vessels. Maintains shape of eye. Protects from external trauma.     

  • Cornea: Part of the refracting media of the eye, bending light rays so they can be focused on the inner retina. Protective. Allows light in. Focus on retina. Must remain clear. Nociceptive pain.

• Middle Vascular Choroid:     

  • Choroid: Has dark pigmentation to prevent light from reflecting internally and is heavily vascularized to deliver blood to the retina. Provides nourishment.     

  • Iris: Functions as a diaphragm, varying the opening at its center. Color tissues. Use muscles to change size of pupil.     

  • Pupil: Round and regular; its size is determined by a balance between the parasympathetic and sympathetic chains of the autonomic nervous system. Determines how much light comes through. Opening at center of iris. Very reactive to light. 3-5 mm.     

  • Lens: A biconvex disc located just posterior to the pupil. It serves as a refracting medium, keeping a focused image on the retina. Size changes with focus. Located behind iris. Elastic. Bulges to focus near and flattens when focusing far.

  • Chambers:         

    • Anterior Chamber: Located posterior to the cornea and in front of the iris and lens. Aqueous humor. Space between cornea and iris. Thin fluid that contains vitamins and proteins. Aids in eye shape, light refraction. Small amount of fluids enters and exits constantly.

      • Can lead to increased intra ocular pressure when not draining properly.         

    • Posterior Chamber: Located behind the iris to the sides of the lens.      

    • Vitreous Body: Contains vitreous humor, a clear, gelatinous substance that occupies the space behind the lens. Largest chamber. Shock receptor maintains shape.

• Inner Nervous Retina:     

  • Retina: The visual receptive layer of the eye in which light waves are changed into nerve impulses.     

  • Optic Disc: The area in which fibers from the retina converge to form the optic nerve. It is located toward the nasal side of the retina. Inside back of eye. Entry point for major blood vessels.

    • Edema is papilledema (due to increased cranial pressure from CSF)     

  • Optic Nerve: Transmits visual information from the retina to the brain.     

  • Macula: Located on the temporal side of the fundus; it is the area of sharpest and keenest vision. Center of retina. Central vision.

    • Fovea Centralis: Area of sharpest vision     

  • Retinal Vessels: These include paired arteries and veins that extend to each quadrant.

Visual Pathways and Reflexes

• Visual Pathways: Light rays are refracted through the transparent media (cornea, aqueous humor, lens, and vitreous body) and strike the retina. The retina transforms the light stimulus into nerve impulses that are conducted through the optic nerve to the visual cortex of the occipital lobe. At the Optic Chiasm, fibers from the nasal half of each retina cross to the opposite side.

• Pupillary Light Reflex: The normal constriction of the pupils when bright light shines on the retina. It is a subcortical reflex (we have no conscious control over it).

• Fixation: A reflex direction of the eye toward an object attracting our attention.

• Accommodation: Adaptation of the eye for near vision. It is accomplished by increasing the curvature of the lens through movement of the ciliary muscles.

Developmental Considerations

Infants and children

    Peripheral vision: Intact but lens is spherical

    Macula: Absent but matures at about 8 months

    Binocular vision: 3-4 months old and can fixate. Reaches adult size at 8 years.

Aging Adult

    Loss of skin elasticity. Loose fat tissue around orbit. Muscles atrophy. Pupil size changes. Lens change and thickens, more rigid, and can’t accommodate for near vision.    

    Presbyopia after age 40 is normal, can’t focus on small and near object so reading glasses may be needed.

    Visual acuity decreases at 50. Adaption to darkness which impacts night driving and increases fall risk.

Subjective Data and Health History

When conducting an eye assessment, practitioners should ask about:

• Vision Difficulty: Any decreased acuity, blurring, or blind spots.

  • Blind spots could be glaucoma compression

  • Halos or rainbows could be pressure

• Pain: Any burning, aching, or sharp pain (noting that some serious conditions like glaucoma are often painless initially).

  • Sudden pain could a loss of vision risk

• Strabismus and Diplopia: History of crossed eyes or seeing double.

• Redness and Swelling: Any inflammation or edema.

• Watering and Discharge: Any irritation or excessive tearing (lacrimation).

• History of Ocular Problems: Past injuries, surgeries, or treatments.

• Glaucoma: Specific history of increased intraocular pressure.

• Use of Corrective Lenses: Use of glasses or contact lenses and how they are maintained.

• Patient-Centered Care: Last vision test and how vision loss affects daily living activities.

• Infants and Children considerations: Vaginal infections in mother at delivery, developmental milestones (is the child following objects?), and safety (protection from sharp objects).

• Aging Adult considerations: Difficulty with climbing stairs or driving at night, presence of cataracts or dryness. Regular eye assessments should be done after age 40

Objective Data: The Physical Exam

Equipment Needed: Snellen eye chart, Handheld vision screener (e.g., Jaeger card), Opaque card or occluder, Ophthalmoscope.

• Test Central Visual Acuity:     

  • Snellen Eye Chart: The most commonly used and accurate measure of visual acuity. The numerator indicates the distance the person is standing from the chart ($20$ feet), and the denominator gives the distance at which a normal eye could have read that particular line.     

    • Example results include a fraction such as $20/40$, meaning the individual can see at $20$ feet what a person with normal vision can see at $40$ feet. This indicates a lower visual acuity, which may require further assessment or referral.

• Test Visual Fields:     

  • Confrontation Test: A gross measure of peripheral vision. It compares the person's peripheral vision with your own.

• Inspect Extraocular Muscle (EOM) Function:     

  • Corneal Light Reflex (Hirschberg Test): Assess the parallel alignment of the eye axes by shining a light toward the person's eyes. The reflection of the light on the corneas should be in exactly the same spot on each eye.

    • Used to test for strabismus.     

  • Cover Test: Detects small degrees of deviated alignment by interrupting the fusion reflex that normally keeps the two eyes parallel.     

  • Diagnostic Positions Test (Six Cardinal Positions of Gaze): Leading the eyes through the six cardinal positions of gaze elicits any muscle weakness during movement.

    • Looks for nystagmus.

• Inspect External Ocular Structures: General inspection of eyebrows, eyelids, lashes, and eyeball alignment.

• Inspect Anterior Eyeball Structures: Examination of the cornea, lens, iris, and pupil.

• Inspect the Ocular Fundus:     

  • Ophthalmoscope: Used to enlarge the view of the eye so the media and ocular fundus can be inspected.     

  • Red Reflex: Caused by the reflection of the ophthalmoscope light off the inner retina.

Developmental Considerations

• Infant Developmental Timeline:     

  • Birth to $2$ weeks: Refusal to reopen eyes after exposure to bright light; alert state may allow for fixing on an object.     

  • $2$ to $4$ weeks: Can fixate on an object.     

  • $1$ month: Can fixate and follow a light or bright toy.     

  • $6$ weeks: Edges of the visual field are perceived.     

  • $3$ to $4$ months: Can fixate, follow, and reach for a toy.     

  • $6$ to $10$ months: Can fixate and follow the toy in all directions.

• Aging Adult:     

  • Visual Acuity: Central acuity may decrease, particularly after $70$ years of age.   

  • Three Common Causes of Decreased Visual Functioning:         

    • 1. Cataracts: A clouding of the crystalline lens from a Josephine of proteins.        

    • 2. Glaucoma: An optic nerve neuropathy characterized by loss of peripheral vision, caused by increased intraocular pressure.         

    • 3. Age-Related Macular Degeneration (AMD): A loss of central vision caused by yellow deposits (drusen) and neovascularity in the macula.    

    • 4. Diabetic Retinopathy: Leading cause of visual impairment in the working-age population.

Abnormal Findings

• Extraocular Muscle Dysfunction:     

  • Asymmetric Corneal Light Reflex: Indicates malalignment.

    • Strabismus     

  • Cover Test failures: Eye jumps to fixate on the designated object.     

  • Diagnostic Positions Test failures: Paralysis or weakness in one or more muscles.

• Eyelid Abnormalities:     

  • Periorbital Edema: Swollen and puffy lids due to fluid accumulation.

    • Common in crying, sinus conditions, heart failure, renal failure, and hyperthyroidism.     

  • Exophthalmos: Protruding eyes.

    • Look surprised all the time. Common in hyperthyroidism     

  • Enophthalmos: Sunken eyes.

    • Due to dehydration, chronic muscle wasting, and malnourishment.     

  • Ptosis: Drooping of the upper eyelid.     

    • Neuromuscular disorder, fatigue, cranial nerve damage

  • Upward Palpebral Slant: Normal in many children but may indicate Down syndrome when combined with other signs.     

  • Ectropion: Lower lid loose and rolling out.

    • Causes excessive tearing and abnormal lubrication     

  • Entropion: Lower lid rolling in.

    • Lower lid may have spasms. Feeling like something is in eye. Can be painful.

• Eyelid Lesions:     

  • Blepharitis: Inflammation of the eyelids. Inflamed crusted eyelids. Staph or dermatitis. Burning or foreign body feeling.     

  • Chalazion: A beady nodule protruding on the lid (infection or retention cyst of a meibomian gland).     

    • Cyst developed from clogged gland. Skin over nodule is movable.

    • Red, inflamed, and tender.

  • Hordeolum (Stye): Acute localized staphylococcal infection of the hair follicles at the lid margin. Very contagious.     

  • Dacryocystitis: Inflammation of the lacrimal sac.

    • Pain, warmth, edema. Purulent drainage coming from tear duct.     

  • Basal Cell Carcinoma: Often presents as a papule with an ulcerated center on the lower lid.

• Pupil Abnormalities:     

  • Anisocoria: Unequal pupil size. Can be congenital.     

  • Monocular Blindness: When light is directed to the blind eye, no response occurs in either eye. When light is directed to the normal eye, both pupils constrict.     

  • Miosis: Constricted and fixed pupils. Common in patients taking meds for glaucoma but can also mean brain damage.     

  • Mydriasis: Dilated and fixed pupils. Could indicate cardiac arrest.

• Advanced Practice / Eye Conditions:     

  • Conjunctivitis (Pink Eye): Infection of the conjunctiva. Allergic, viral, or bacterial    

  • Allergic Conjunctivitis: Inflammation due to allergens.     

  • Color Discrimination: Assessment of the ability to distinguish colors, often tested using Ishihara plates or similar tests.