Introduction

Acute vision is vital to the success of the competitive athlete, and even “minor” eye disorders will sideline most athletes. An athletic trainer must understand the basic anatomy and physiology of the eye, be able to perform a basic eye examination, and know the common sport-related eye conditions and injuries for which referral to an eye care specialist is appropriate. This chapter discusses the structures of the eye, examination techniques for both healthy and injured eyes, and the pathological eye conditions that many athletic trainers might encounter.

Overview of Anatomy and Physiology of the Eye

The anatomy of the eye consists of external and internal structures. All structures are contained within the bony eye socket. The eye socket (Figure 12-1), anatomically known as the bony orbit, comprises four walls made up of seven different facial bones of the skull, connective tissue, fat, blood vessels, and nerves.

Anteriorly, the orbit rim is created by the frontal, zygomatic, and maxillary bones (see Figure 11-1). The sphenoid, lacrimal, ethmoid, and maxillary bones form the posterior and medial aspects of the orbit. The palatine, zygomatic, and maxillary bones create the floor of the orbit, and the zygomatic and sphenoid bones form the lateral aspect. The orbit provides protection for the eyeball (globe) and contains the lacrimal gland, which produces the tears that lubricate and rinse the surface of the eye. The bony orbit also provides anchorage for the six small extraocular muscles that move the eye. The optic nerve passes through the posterior aspect of the orbit. The visual cortex is located in the occipital lobe of the brain.

The external eye includes the eyelid, the conjunctiva, and the lacrimal gland (Figure 12-2). These structures serve to protect the eye from foreign objects and to distribute tears evenly across the eye. The eyelids provide protection for the external surface of the eye. They help lubricate the ocular surface with their blinking action. The eyelid skin is the thinnest skin of the body. Within each eyelid is a relatively rigid tarsal plate containing meibomian glands, which secrete the oily component of the three-layered tear film. The conjunctiva is a thin, essentially transparent, highly vascular mucous membrane that covers the anterior sclera and the posterior surfaces of both the upper and lower eyelids.

The eye consists of the sclera, cornea, iris, lens, retina, choroid, optic disk, and macula (Figure 12-3). The sclera is the dense white connective tissue that makes up more than 90% of the outer layer of the globe and provides structure for the contents of the eyeball. The cornea serves as the barrier between the environment and the aqueous humor. The cornea is made up of several layers and is the clear window of the eye through which light passes. The iris creates the color of the eye. The pupil is the round, central opening in the iris that creates a pathway for light to reach the retina. This aperture dilates or constricts to regulate the amount of light that enters the eye. Between the cornea and the iris is the anterior chamber. This space is filled with a clear fluid known as aqueous humor.

The crystalline lens is a round, transparent tissue located directly behind the iris. Tiny filaments called zonules, which are attached to the ciliary body, suspend the lens and control its thickness by contracting or relaxing it, allowing the image to be focused onto the retina. The ciliary body is responsible for production of the aqueous humor that fills the anterior chamber of the eye. The large space behind the lens is filled with the transparent gelatinous fluid of the eye known as the vitreous humor.¹

The retina is the thin, transparent membrane lining the back of the eye that receives light and sends the initial visual signal through the optic nerve to the brain, where it is processed and interpreted. Between the retina and the sclera is the vascular tissue called the choriocapillaris. The choriocapillaris supplies blood and nourishment to the outer layers of the retina. The “red eye” seen in a photograph is caused by the reflection of the camera flash through a dilated pupil against the choriocapillaris. As the nerve fibers from the retina exit the eye through the optic nerve, they bunch together at the origin of the optic nerve to form the optic disk. The optic disk is the visible portion of the optic nerve that can be seen when examining the eye. The other structure that can be seen during examination with an ophthalmoscope is the macula and its center point, the fovea, which is considered the site of central vision and color perception of the eye. The majority of color receptors, called cones, are found in the macula (Figure 12-4).²,³

The most important part of an eye examination is the testing of visual acuity. The ability of the eye to focus clearly on distant or near objects is directly related to the structural integrity of all its parts. Visual acuity is assessed while the patient wears his or her spectacles or contact lenses for distance vision. The Snellen chart (Figure 12-5, A) is a quick and easy-to-use screening tool for far vision. The chart contains graduated sizes of letters with standardized acuity numbers at the end of each line. The patient is asked to read the lines of the chart while standing 20 feet away and covering one eye. The Snellen visual acuity is recorded as a fraction comparing the patient’s performance with the standard or “normal” person’s performance. The first number, or numerator, represents the patient’s distance from the eye chart, which should be 20 feet, and the second number, or denominator, represents the distance at which a normal person can read the same-size letter or letters on the same line of the chart. For example, reading the 20/40 line (from 20 ft away) indicates that the patient can see a specific-sized letter at 20 feet⁴, whereas a person with normal visual acuity can see the same-size letter from 40 feet away, thus revealing that the athlete has suboptimal acuity.¹,⁵ One must remember that this is a screening tool for far visual acuity only and does not measure near vision or dynamic visual acuity. Referring a patient to an optometrist or ophthalmologist for a complete visual assessment may be warranted. Each eye is tested independently, with the other eye occluded with the palm of one hand or an opaque object. When testing acuity in children or nonreaders, an illiterate E or C or picture chart is used (Figure 12-5, B).

If a standard eye chart is not available, a near-vision card can be used to assess visual acuity (Figure 12-6). These small cards can be easily added to a standard first-aid kit. If near vision is tested, then the patient should wear reading glasses or bifocals if he or she typically requires corrective lenses to read. In lieu of a vision card or a Snellen chart, a common alcohol prep pad may be used to test visual acuity (Figure 12-7).

When a patient cannot see the largest letters of an eye chart, the clinician may hold up some of the fingers of one hand and ask the patient to count them at progressively closer distances to the eye. This is documented as “count fingers vision at [for example] 2 feet.” If the patient cannot count the fingers, the examiner can wave a hand in front of the eye and ask if the patient can detect the motion. This is documented as “hand motion vision.” If the patient cannot detect hand motion, any bright light source (e.g., a penlight) can be used to determine ability to detect light. This is documented as “light perception vision.” Reduction of visual acuity in an injured eye is a serious ocular emergency. Immediate referral to an eye care specialist is warranted.

Testing Pupillary Responses

The ability of the pupil to react to light is a basic feature of a normal functioning ocular system. Brisk pupil constriction in response to a bright light also suggests the presence of vision in the absence of any standard eye chart. While the patient is looking into the distance, a light is moved in toward the eye from the side and shined directly into the pupil (Figure 12-8). The speed (briskness) of the pupillary constriction is noted. Each eye is examined separately and should have similar findings.

After examining each eye for its light reactivity and responsiveness, the examiner performs a swinging light test by swinging a light from the normal eye to the injured one. This test is based on the fact that the same quantity of light (i.e., from the same light source) should constrict each pupil by the same amount. When internal ocular damage or optic nerve damage occurs in one eye, the pupil of the injured eye will appear to dilate when the light is moved from the normal eye to the injured eye, indicating that the same amount of light is not being transmitted through the optic nerve in the injured eye. This is known as an afferent pupillary defect and represents a potentially severe ocular emergency. Immediate referral to an eye care specialist is warranted.

A pupil that is larger in the injured eye or that does not react to light (i.e., traumatic mydriasis) or a pupil that is no longer round (e.g., peaked or oval) may represent significant intraocular trauma (e.g., traumatic iritis). Immediate referral to an eye care specialist is warranted. It is important for the athletic trainer to know if the athlete has a previously existing or congenitally larger pupil on one side, or anisocoria, because this may confuse the findings of the examination.

Testing Extraocular Muscle Motility

Part of the basic assessment of an patient’s eye is the examination of ocular motility. The inability of one or both eyes to move into the cardinal fields of gaze (Figure 12-9), especially after an eye injury, indicates a severe eye injury with possible eye socket pathology or entrapment of the extraocular muscles (Figure 12-10).⁶ The examiner asks the patient to follow an object or a fingertip up, down, left, and right with both eyes together. The examiner assesses the patient for smooth, uninterrupted movements of both eyes in all fields of gaze. There should be no restriction of gaze in either eye; movements of the two eyes should be harmonious and parallel. Any alteration of extraocular movements after an injury may also represent a variety of neurological conditions and requires immediate medical attention.⁷

Testing Peripheral Vision

Although arguably not as crucial as central visual acuity, peripheral vision allows athletes to view the entire field of sport around them and to see where their teammates or competitors might be while they focus their vision centrally. It is important that the range of an athlete’s peripheral vision be known before any injury (i.e., preparticipation peripheral vision testing).

The method most often used to grossly test peripheral vision is called confrontation visual field testing (Figure 12-11). The examiner tests the patient, peripheral vision one eye at a time. To test the right eye, the examiner sits approximately 3 feet directly in front of the patient. The patient, left hand over left eye, focuses only on the examiner’s left eye. Conversely, the examiner’s right eye is closed. This allows the examiner to watch his or her own open hands during the examination while fixating on the patient’s right eye.

The examiner holds up one, two, or three fingers on each hand, equidistant between the examiner and the patient and equidistant on either side of the direct line of sight between the athlete’s right eye and the examiner’s left eye. Examiners must be able to see their own fingers during this kind of examination. The patient is asked to add the total number of fingers seen while fixating only on the examiner’s left eye and without looking at the examiner’s fingers. The examiner will be able to detect whether the patient looked away from the examiner’s left eye. It is best not to hold up the same number of fingers on each hand at the same time. This will allow the examiner to know exactly which field of vision was defective. Next, the other eye is examined in a similar fashion. All the cardinal fields of vision—right, left, above, below, above and to the right, above and to the left, below and to the right, and below and to the left—need to be tested. Any finding of the patient’s inability to see in a particular field of vision should be referred to an eye care specialist before participation.

Examining the Anatomical Structures of the Injured Eye

A good assessment of the eye can usually be made by simply having the patient open his/her eyes and examining them directly. On occasion, the eyelids may have to be held apart by either the patient or the examiner. Eyelid swelling is a common consequence of direct trauma to the eye. Therefore the eye must be examined as soon as possible before swelling of the eyelids makes direct assessment impossible.

The examiner can use room lighting or a directed source of light (e.g., a flashlight or penlight) to assess the anterior portion of the ocular anatomy (Figure 12-12). Inspection of the lids and palpation of the bony orbital rim can reveal serious trauma after a blunt injury. If there is any suspicion that the trauma was severe enough to penetrate or rupture the eyeball then no external pressure should ever be placed on the eye or surrounding structures (i.e., eyelids).

A light is directed toward the patient’s opened eye; the patient is asked to look up while the examiner retracts the lower lid (Figure 12-13, A) and to look down while the examiner retracts the upper lid (Figure 12-13, B). This facilitates examination of the entire anterior aspect of the globe including the conjunctiva, sclera, cornea, and iris. Foreign bodies are commonly found in the conjunctival fornices. The fornices are the most posterior portions of the upper and lower portions of the conjunctiva, where the conjunctiva overlying the sclera (bulbar conjunctiva) and the conjunctiva lining the eyelids (palpebral conjunctiva) join together.

Obscuration of the structures behind the cornea (e.g., iris or lens) because of a cloudy anterior chamber is an ominous sign of potential blood in the anterior chamber (i.e., hyphema). This can frequently be detected with a penlight and indicates a very serious eye injury. If the eye is anatomically distorted or bleeding, it is prudent to discontinue any further palpation or examination and to seek emergency medical attention and urgent ophthalmological referral.

Examining the Eye With the Ophthalmoscope

The ophthalmoscope is an instrument used to view the internal structures of the eye. The head of the instrument contains a light source, which allows the examiner to visualize the inner eye through a series of lenses and apertures to allow for near or far focusing (Figure 12-14). The most commonly used aperture projects a large, round beam. Other apertures include the small aperture, the slit-lamp aperture to examine the anterior eye, the red-free filter aperture that shines a green beam to check the optic disk, and the grid aperture used to estimate size of fundal lesions.⁷

The diopter (magnification power of the lens) of the ophthalmoscope may be changed by turning the lens selector disk to the corresponding magnification.¹,² The black numbers indicate positive magnification power, and the red numbers show the negative. Turning the wheel clockwise selects positive lenses, and rotating it counterclockwise selects negative lenses. Lens numbers range in magnification power from ±20 to ±140. The range of plus and minus lenses can compensate for myopia or hyperopia in both the examiner and the patient.⁷ It is interesting to note that the abbreviations seen on a prescription for corrective lenses refer to the right and left eyes: oculus dexter (OD) for the right eye and oculus sinister (OS) for the left eye.

The heads of both the ophthalmoscope and the otoscope (used to view the ear and nose) typically share a common handle containing a rechargeable battery. The heads are interchangeable and can easily be converted from one instrument to the other. To change from an otoscope head to an ophthalmoscope head, the examiner pushes down on the head that is currently on the handle while turning to unlock the attachment, inserts the other head, and fastens it to the handle in the same manner.

Both instruments are turned on in the same way, namely, by pushing the on/off switch while turning the black rheostat clockwise to the desired intensity of light.

To examine a patient’s eye with the ophthalmoscope, the athletic trainer turns on the ophthalmoscope and selects the large aperture. This should project a large round light on the examiner’s hand or the wall. Next the room is darkened. The examiner holds the handle of the ophthalmoscope in the right hand (to examine the patient’s right eye) with the index or middle finger on the lens selector wheel. To examine the left eye, the left hand is used. The ophthalmoscope is held firmly against the bony orbit of the examiner’s eye (right eye for examining the patient’s right eye and left eye for the patient’s left eye) with the handle tilted laterally. This will prevent the athletic trainer and the patient from bumping noses during the examination (Figure 12-15).

The patient is instructed to look up over the shoulder of the athletic trainer. The examiner should start about 15 inches away from the patient, shining the light into the eye to visualize the reddish orange “glow” (red reflex) of the eye. The athletic trainer should approach the patient from the lateral side (at about a 15-degree angle). Shining the light directly into the patient’s eye must be avoided because it will cause the pupil to constrict, making it more difficult to visualize the internal eye through an undilated pupil. While keeping the light focused on the red reflex, the athletic trainer moves in close to the eye, almost touching the patient’s eyelashes. Absence of a red reflex is often the result of an improperly positioned ophthalmoscope.

To view the internal structures of the eye, such as the optic disk, arteries, veins, and retina, the athletic trainer may need to turn the lens selector wheel to focus on various structures. If the patient is myopic, a minus (red) lens will be used (Box 12-1). The fundus or retina will appear as a yellow or pink background with blood vessels branching away from the optic disk (see Figure 12-4). It is often easier to find the blood vessels and follow them back to the optic disk than to try to locate the optic disk by itself. The arterioles are smaller than the venules and reflect brighter light. The vessels should be followed as far as possible

BOX 12-1   USING THE OPHTHALMOSCOPE

During examination of the internal structures of the eye with an ophthalmoscope, the lens selector wheel is used and adjusted so that the examiner can focus on the retina. Depending on whether the patient’s, or the examiner’s, eye is myopic or hyperopic, the dial on the lens selector wheel is turned to either the red or black numbers. Each number represents the strength of each lens in the wheel, measured in diopters. The red numbers indicate concave lenses used to neutralize myopia, and the black numbers indicate convex lenses used to neutralize hyperopia.

Normal Eye

The diopter is set at zero (clear glass) when both the patient’s and the examiner’s eyes are normal.

Myopia (Nearsighted)

Because the globe is longer in the nearsighted person than in the normal eye, the lens selector wheel is moved to the red numbers (concave lens) to adjust for myopia in either the patient or the examiner.

Hyperopia (Farsighted)

The globe in a hyperopic eye is shorter than normal. The black numbers (convex lens) on the ophthalmoscope lens selector wheel are used so that the focal point is on the retina.

Modified from Jarvis C: Physical examination & health assessment, ed 5, Philadelphia, 2008, Saunders.

KEY POINTS RETINAL VESSELS

The eye is the only place in the body where the blood vessels may be viewed directly through the use of an ophthalmoscope. Many systemic diseases that affect the vascular system may show signs in the retinal vessels.

in each of the four quadrants of the eye (i.e., superior, inferior, nasal, and temporal) as they go away from the optic disk. When the optic disk is visualized, it should appear yellow to creamy pink but may be darker in dark-skinned individuals. The borders of the disk should be sharp and well defined. Moving in a temporal direction from the optic disk, the macula (fovea centralis) may be able to be visualized.⁴ To bring the fovea into the field of vision, the examiner asks the patient to look directly at the light of the ophthalmoscope. It will appear as a yellow dot surrounded by a deep pink periphery and will not have any blood vessels running through it.² Considerable practice is needed to visualize the macula, and it may be impossible to view without the pupil being dilated.

For clear vision, both near and distant images must be sharply focused onto the retina, which lines the back of the eyeball. The ability of the eye to focus these images is directly related to the length of the eye, the curvature of the cornea, the clarity of the ocular media, and the flexibility of the crystalline lens. The first two parameters, length of eye and curvature of cornea, determine the refractive error of an eye. Myopia, or nearsightedness, is produced by a longer than normal eye. A distant object is focused in front of the retina instead of on it (Figure 12-16, A). Hyperopia, or farsightedness, is produced by a shorter than normal eye (Figure 12-16, B). A distant object is out of focus when it reaches the retina and, theoretically, focuses behind the retina.⁸ The shape of the cornea is typically spherical (just like a tennis ball) on its anterior curvature. When this curvature is not spherical and has multiple curvatures (such as an egg or football), the eye is considered astigmatic⁸ (i.e., astigmatism; Figure 12-16, C). After the age of 40 years, the crystalline lens inside the eye loses its flexibility and the ability to focus on near objects. This is known as presbyopia. Presbyopic patients require reading glasses for near vision.

Conjunctivitis

Conjunctivitis is a general term for an inflammation of the conjunctiva, the transparent, vascular tissue covering the anterior sclera and the posterior surface of the eyelids. It is commonly caused by bacteria, viruses, allergies, or dry eye or as a response to a corneal injury or irritation.

Signs and Symptoms

The symptoms of conjunctivitis, sometimes called pink eye, are not specific to the causative agent and can include all or some of the following: redness, burning, itching, tearing, irritation, and foreign body sensation (Box 12-3). Allergic conjunctivitis is classically characterized by itching. Viral conjunctivitis is often associated with recent cold or flu symptoms or recent contact with someone with a red eye.¹¹,¹² The most obvious signs of conjunctivitis are redness or vascular engorgement (Figure 12-17). There may be a discharge, ranging from watery to mucoid to frank purulence (pus). Redness of the conjunctiva in the space between the eyelids associated with a burning sensation is common after exposure to sun, wind, or dusty conditions, which are all common to outdoor athletics.

BOX 12-3   EVALUATION OF RED EYE

Follow these steps to assess the need for referral of a patient with red eye:

1. Check the athlete’s visual acuity.

2. Inspect for a pattern of redness. A diffuse “pink” color is quite different from a deep localized redness.

3. Observe for the presence of discharge.

4. Use a fluorescein stain and blue cobalt light to observe for corneal defects if an abrasion is suspected.

5. Use an ophthalmoscope to observe the inner structures of the eye for irregularities.

6. Refer a patient with any abrasions, foreign bodies, hyphemas, or irregularities in the shape of the pupil to an eye care specialist immediately.

Modified from Black JM, Hawks JH: Medical–surgical nursing: clinical management for positive outcomes, ed 7, St. Louis, 2005, Elsevier, p 1920.

Referral and Diagnostic Tests

Viral conjunctivitis is highly contagious, and therefore referral to an eye care practitioner for diagnosis is important in most cases of conjunctivitis. Without the benefit of a slit-lamp biomicroscope used by the ophthalmologist or optometrist, determining the exact cause of conjunctivitis may be difficult (Box 12-4).

BOX 12-4   THE CAUSE OF RED EYE

Athletic trainers often encounter athletes whose chief complaint is of a “red eye.” An engorgement of the conjunctival vessels causes the eye to be red. It may be associated with a subconjunctival hemorrhage that requires no treatment, or it may be a manifestation of a serious eye disorder that requires immediate attention. Common disorders involving red eye include the following:

Conjunctivitis: Bacterial, viral, allergic, and irritative

Herpes simplex keratitis: Inflammation of the cornea caused by a herpesvirus

Scleritis: Inflammation of the sclera

Subconjunctival hemorrhage: Accumulation of blood in the potential space between the conjunctiva and the sclera

Abrasions and foreign bodies: Hyperemic response

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