22.2 Eyes

External Structures

External structures of the eye consist of the following:

• Eyebrow: The eyebrow is the hair-covered ridge above the eye that helps protect the eye from sweat and direct sunlight.
• Eyelid: The eyelid is the movable fold of skin and muscle that covers and protects the front of the eye.
• Eyelashes: The eyelashes are short hairs along the eyelid edges that help prevent debris from entering the eye.
• Conjunctiva: The conjunctiva is a thin, transparent membrane covering the front surface of the eye (except the cornea) and the inner surface of the eyelids.
• Cornea: The cornea is the clear, dome-shaped front surface of the eye that focuses light onto the lens and retina.
• Sclera: The sclera is the white, tough outer covering of the eye that helps maintain its shape and protect its inner structures.
• Iris: The iris is the colored part of the eye that controls the size of the pupil and regulates the amount of light entering the eye.
• Pupil: The pupil is the black circular opening in the center of the iris that allows light to enter the eye.
• Lacrimal gland: The lacrimal gland produces tears that keep the eye moist and help with lubrication, nourishment, and protection against infections.
• Lacrimal ducts: The lacrimal duct drains tears from the eye’s surface to the nasal cavity.

Internal Structures

Internal structures of the eye consist of the following:

• Lens: The lens is a transparent, flexible structure located behind the iris. It changes shape to focus light onto the retina.
• Ciliary muscle: The ciliary muscle controls the shape of the lens to help with focusing on near and distant objects (accommodation).
• Vitreous humor: The vitreous humor is a gel-like substance that fills the larger space within the eye, helping maintain its shape and providing support to the retina.
• Retina: The retina is the innermost layer of the eye that contains specialized cells called photoreceptors (rods and cones) that detect light and transmit visual signals to the brain.
• Cones: A cone is a photoreceptor that is primarily responsible for color vision and visual acuity (sharpness).
• Rods: A rod is a photoreceptor that is responsible for vision in low-light conditions and for detecting movement.
• Macula: The macula is the small, central area of the retina responsible for central vision and color perception.
• Optic nerve: The optic nerve is a bundle of nerve fibers that carries visual information from the retina to the brain for processing.
• Optic disc: The optic disc is the area where the optic nerve exits the retina; it lacks photoreceptors, creating the “blind spot.”

Movement of the eye within the orbit occurs by the contraction of six extraocular muscles that originate from the bones of the orbit and insert into the surface of the eyeball. The extraocular muscles are innervated by the abducens nerve, trochlear nerve, and oculomotor nerve (cranial nerves III, IV, and V).

Vision

The process of vision is a complex and intricate interaction involving various structures within the eyes, brain, and neural pathways. From the visual fields that encompass our surroundings to the intricate neural pathways that relay information to the brain, and to the reflexes that adapt our visual experience to changing conditions, each facet of this process contributes to our profound sense of sight. Key elements of vision include visual fields, visual pathways, and visual reflexes.

Assessing the Pupils

Inspecting the pupils is an important part of a nursing assessment, as it can provide valuable information about a person’s neurological and ophthalmic health. To assess the pupils, ensure proper lighting in the room (dim lighting can help with assessing pupil size). Wash your hands and don gloves. Explain the procedure to the patient to ensure their cooperation and comfort. Position the patient comfortably sitting or lying down, facing you.

Begin by assessing the patient’s overall level of alertness and consciousness. A patient who is not fully alert may have different pupil responses. Ask the patient to look straight ahead, keeping their gaze focused on a distant object. Hold the penlight or flashlight about 12 to 15 inches away from the patient’s face and shine the light directly into one eye. Observe both pupils for their initial size and equality. They should be of equal size and react similarly to light. On average, a normal adult pupil is approximately 2 to 4 millimeters in bright lights and 4 to 8 millimeters in dark spaces. Note any differences in size between the two pupils. Test the pupil’s reaction to light by shining the light directly into one pupil and observing the response. The illuminated pupil should constrict briskly, and the opposite pupil should also constrict when light is shone into the other eye. If one or both pupils do not constrict or if the response is sluggish, it may indicate an abnormality in the neurological or ophthalmic system.

To test pupil accommodation, ask the patient to focus on a near object (e.g., your finger) and then switch their focus to a distant object. Observe the pupils for changes in size. The pupils should constrict when focusing on a near object and dilate when focusing on a distant object. If the pupils do not react as expected during accommodation, it may indicate a dysfunction in the pupil’s response to changes in focus.

Visual Acuity

Assessing visual acuity is a crucial aspect of a comprehensive eye examination. The visual acuity measures a person’s ability to see details at a specific distance. Visual acuity includes both far and near vision assessments.

To assess far-distance vision, ensure the room is well lit and the patient is wearing any corrective lenses they normally use (glasses or contact lenses). Explain to the patient they will be asked to read letters or symbols on a chart to assess their ability to see details. Far-distance acuity is measured using the Snellen chart (Figure 22.18) at a distance of 20 feet (6 meters) in the United States. The Snellen chart consists of rows of letters or symbols, with the largest and most visible letters at the top and progressively smaller ones below. Instruct the patient to cover one eye and read the letters from the top row to the bottom until they can no longer correctly identify the letters or symbols. Visual acuity is recorded as a fraction. The top number represents the distance at which the chart is viewed (20 feet), and the bottom number indicates the distance at which a person with normal vision can read the line. For example, if the patient can read the line labeled “20/40,” it means they can see at 20 feet what a person with normal vision can see at 40 feet.

Figure 22.18 A Snellen chart is used to assess distance vision. (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

To assess near vision, explain to the patient that you will be assessing their ability to read small print at a close distance. A near vision chart, such as a Jaeger card (Figure 22.19), consists of paragraphs of text with varying font sizes. Ask the patient to hold the Jaeger card 14 to 16 inches from their eyes and read aloud the text on the chart starting from the largest font size. Proceed to smaller font sizes until the patient can no longer comfortably read the text. Note the font size at which the patient is able to read comfortably. For example, if they can read text labeled “J5,” it means they can read text that is typically readable by a person with normal vision at a distance of 5 inches.

Figure 22.19 A Jaeger card is used to assess near vision. (credit: “111012-F-ZT401-067.JPG” by Airman 1st Class Brooke P. Beers, Public Domain)

Extraocular Movements

Assessing extraocular movement is an essential part of a neurological and ophthalmic examination. These movements involve the coordinated actions of the six muscles that control each eye’s movement and alignment. Ensure proper lighting in the room and position the patient comfortably sitting or lying down, facing you. Explain to the patient that you will be assessing their eye movements to ensure their eyes can move smoothly in different directions. Test the six cardinal directions of gaze by asking the patient to keep their head still and follow a target (your fingertip or a pen) with their eyes only, without moving their head. Instruct the patient to focus on the target as you move it through the six cardinal directions of gaze: right (lateral), left (lateral), up (superior), down (inferior), upper-right diagonal, and upper-left diagonal. While the patient is tracking the target with their eyes, observe their eye movements for smooth and coordinated motions in each direction. An involuntary, rhythmic, back-and-forth movement of the eyes is termed nystagmus and is considered abnormal.

To test convergence, ask the patient to focus on an object (e.g., your fingertip) held about 2 inches in front of their nose. Slowly move the object toward the patient’s nose while instructing them to keep looking at the object. Observe their eyes for convergence, where both eyes move inward. Abnormal findings, such as limited eye movements, jerky motions, or nystagmus, may indicate issues with the extraocular muscles, issues with the cranial nerves (particularly cranial nerves III, IV, and VI), or neurological problems.

Peripheral Vision

Assessing peripheral vision, also known as visual field, is important for detecting any abnormalities or defects in a person’s ability to see objects in their side or peripheral vision. Ensure adequate lighting and seat the patient comfortably facing you, at eye level. Explain to the patient that you will be testing their ability to see objects in their side vision. To conduct the confrontation test, instruct the patient to cover one eye. Instruct the patient to keep their gaze fixed on your nose or another reference point in the center. Hold your hands or an object in each of the four quadrants of the patient’s visual field: superior, inferior, temporal (side), and nasal (side). Ask the patient to tell you as soon as they see your fingers or the object you are holding in their peripheral vision. They should not look directly at the objects but should maintain their gaze on the center. Compare the patient’s responses to the objects in each quadrant of the visual field to assess whether their peripheral vision is intact. If the patient consistently misses objects in certain quadrants, it could indicate peripheral vision deficits or defects, which may warrant further evaluation by an eye care professional or a more detailed visual field test. Assessing peripheral vision is crucial for detecting conditions like glaucoma, retinal disorders, and neurological issues that can affect peripheral vision.

Validating and Documenting Data

Data should be validated if discrepancies exist between subjective and objective data, significant changes occur between visits, or highly abnormal findings are noted. To validate the data, the nurse may need to repeat the physical assessment and clarify the subjective findings with the patient. Other times, the nurse may need another nurse or healthcare professional to verify the findings.

Accurate documentation is needed to promote effective communication among the interdisciplinary team. Documenting the results of an eye assessment begins with the chief complaint or reason for the assessment, whether it is routine, due to specific symptoms, or as part of a larger medical evaluation. Document the appearance of the eyes, eyelids, eyebrows, and surrounding skin. Note any swelling, redness, lesions, or abnormalities. Describe the color, texture, and any signs of inflammation, infection, or discoloration. Note the clarity of the cornea and any irregularities. Observe the color and shape of the iris. Measure and record the size of the pupils, documenting any irregularities, such as unequal sizes. Record observations of eye movements, smoothness, coordination, and the presence of nystagmus. Record the results of visual acuity tests (Snellen chart or other methods) for both near and far vision. Document the response of the pupils to light stimuli. Note if they constrict (miosis) in bright light and dilate (mydriasis) in dim light. Describe the patient’s ability to focus on a near object and how the pupils constrict during this process. Document any additional tests that were performed, such as color vision, depth perception, or visual field tests, and also document the results.

Abnormalities of the External Eye

Abnormalities of the external eye refer to various visual, structural, or functional deviations from the normal appearance and function of the eye’s outer structures. These abnormalities can result from various eye conditions, injuries, infections, or systemic disorders. Common abnormalities of the external eye, including conjunctivitis (pink eye), hordeolum (stye), chalazion, ptosis, ectropion, and exophthalmos can be found in Table 22.3.

Condition	Description	Visual Example
Conjunctivitis (also, pink eye)	Inflammation of the conjunctiva (thin membrane covering the sclera and inner eyelids) due to infections (bacterial, viral, or allergic), causing redness, itching, discharge, and tearing	(credit: “Swollen eye with conjunctivitis” by “Tanalai”/Wikimedia Commons, CC BY 3.0)
Hordeolum (also, stye)	A painful, localized infection or inflammation of an eyelid gland, resulting in a red, swollen lump along the eyelid’s edge	(credit: “Stye02” by Andre Riemann/Wikimedia Commons, Public Domain)
Chalazion	A noninfectious bump on the eyelid caused by a blocked meibomian gland, leading to localized swelling, tenderness, and sometimes blurred vision	(credit: “Chalazion” by “jd”/Wikimedia Commons, Public Domain)
Ptosis	Drooping of the upper eyelid due to weakened or paralyzed levator muscles, which can partially obstruct vision	(credit: “Congenitalptosis” by “Andrewya”/Wikimedia Commons, Public Domain)
Ectropion	Outward turning of the lower eyelid, leading to exposure of the inner eyelid and increased risk of dryness and irritation	(attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)
Exophthalmos	One or both eyeballs bulge or protrude abnormally from the eye sockets (orbits)	(credit: “Proptosis and lid retraction from Graves’ Disease” by Jonathan Trobe, M.D./Wikimedia Commons, CC BY 3.0)

Table 22.3 Abnormalities of the External Eye

Abnormalities of the Internal Eye

Abnormalities of the internal eye refer to various disorders and conditions that affect the structures within the eye, including the retina, optic nerve, vitreous humor, and other components. These abnormalities can lead to changes in vision, visual disturbances, and potential vision loss. Common abnormalities of the internal eye include the following:

• Pterygium: A pterygium is a growth of tissue on the conjunctiva that can extend onto the cornea, often caused by excessive ultraviolet (UV) light exposure and leading to redness, irritation, and potential visual disturbances.
• Corneal abrasions or scars: A corneal abrasion is a scratch or injury to the cornea’s surface, while a corneal scar is tissue that forms after the healing of a deeper injury. Both can cause pain, discomfort, and changes in vision.
• Cataracts: A cataract is a clouding of the eye’s natural lens, leading to gradual vision loss, glare sensitivity, and decreased color perception (Figure 22.20).

  Figure 22.20 (a) A cataract causes the natural lens in the eye to become cloudy, causing blurred vision of (b) an originally clear image. (credit a: “Eye disease simulation, myopia.jpg” by National Eye Institute, National Institutes of Health, Public Domain; credit b: “Normal vision” by National Eye Institute, National Institutes of Health, Public Domain)
• Irregularly shaped iris: An irregularly shaped iris is observed when the colored part of the eye that surrounds the pupil has irregular contours, which can be congenital or associated with certain eye conditions.
• Mydriasis: In mydriasis, there is abnormal dilation of the pupil, often due to medication, neurological issues, or eye trauma (Figure 22.21).

  Figure 22.21 Individuals with mydriasis, or benign episodic unilateral mydriasis, will exhibit a dilated pupil in one eye and may also experience mild headaches, eye pain, sensitivity to light, and blurred vision. (credit: modification of work from Anatomy and Physiology. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)
• Anisocoria: In anisocoria, there are unequal pupil sizes in both eyes, which can be normal or a sign of underlying neurological or eye problems.
• Miosis: In miosis, there is abnormal constriction of the pupil, often due to medication, bright light, or neurological conditions.
• Papilledema: In papilledema, there is swelling of the optic disc at the back of the eye due to increased intracranial pressure, which can be a sign of serious conditions like intracranial tumors or head injuries.
• Glaucoma: The term glaucoma is used for a group of eye disorders characterized by increased intraocular pressure that damages the optic nerve, causing gradual peripheral vision loss and potential blindness (Figure 22.22).

  Figure 22.22 Someone who has glaucoma will gradually lose peripheral vision but retains central vision, which makes their vision similar to looking into a tube where things straight ahead appear clearly, but the sides look blurry or darkened. (credit: “Eye disease simulation, glaucoma.jpg” by National Eye Institute, National Institutes of Health, Public Domain)
• Optic atrophy: In optic atrophy, there is degeneration of the optic nerve fibers, leading to vision loss and pale optic discs on examination.
• Macular degeneration: In macular degeneration, there is gradual and progressive damage to the macula, which can lead to significant vision loss and impairment of daily activities that require clear central vision, such as reading and recognizing faces (Figure 22.23).

  Figure 22.23 Visual changes associated with macular degeneration include blurred or distorted central vision, dark or empty spots in the central vision, and straight lines that appear wavy or crooked. (credit: “Eye disease simulation, age-related macular degeneration.jpg” by National Eye Institute, National Institutes of Health, Public Domain)

Visual Abnormalities

Common visual abnormalities that individuals might experience include the following:

• Myopia (nearsightedness): In myopia (nearsightedness), distant objects appear blurry, while close objects are clear. It occurs when light focuses in front of the retina instead of directly on it.
• Hyperopia (farsightedness): In hyperopia (farsightedness), distant objects are clearer than close ones. Light focuses behind the retina instead of directly on it.
• Astigmatism: With an astigmatism, blurred or distorted vision is due to an irregularly shaped cornea or lens, causing light to focus on multiple points rather than a single point.
• Presbyopia: In the age-related condition presbyopia, an individual has difficulty focusing on close objects due to a gradual loss of the eye’s ability to change focus.
• Color blindness: Individuals with color blindness have difficulty distinguishing certain colors, often red and green or blue and yellow, due to a genetic deficiency in color-sensitive cone cells.
• Amblyopia (lazy eye): In amblyopia (also, lazy eye), there is reduced vision in one eye due to improper development during childhood, often caused by unequal refractive errors or strabismus (misaligned eyes).
• Strabismus: Individuals with strabismus have misalignment of the eyes, causing one eye to turn inward, outward, upward, or downward while the other eye remains focused.
• Diplopia (double vision): When an individual has diplopia (double vision), they see two images of a single object. This is often caused by misalignment of the eyes, neurological issues, or eye muscle problems.
• Floater: A floater is a small, semitransparent spot or shape that appears to “float” in the field of vision due to debris in the vitreous humor.
• Flash: A flash is a brief, flickering light or sensation that occurs in the visual field, often caused by traction on the retina or vitreous humor.
• Photophobia: An individual who has photophobia has sensitivity to light, leading to discomfort and squinting in bright environments.
• Night blindness: An individual who has night blindness has difficulty seeing in low-light conditions due to reduced function of the rod cells in the retina.
• Halo: A halo is a glowing circle or ring around a light source, often seen by individuals with cataracts or after refractive surgery.