MUSCLE	FUNCTION	CRANIAL INNERVATION
EXTRINSIC MUSCLES OF THE EYE
Inferior rectus	Rotates eyeball downward and medially; adducts	Oculomotor nerve (III)
Lateral rectus	Rotates eye laterally; abducts eyeball	Abducens nerve (VI)
Medial rectus	Rotates eye medially; adducts eyeball	Oculomotor nerve (III)
Superior rectus	Causes eye to look up	Oculomotor nerve (III)
Inferior oblique	Rotates eyeball upward and outward; abducts	Oculomotor nerve (III)
Superior oblique	Rotates eyeball downward and outward; abducts	Trochlear nerve (IV)
INTRINSIC SMOOTH MUSCLES OF THE EYE
Ciliary muscle	Regulation of lens shape for close vision	Oculomotor (III)
Iris (radial muscles)	Sympathetic stimulation; dilation of pupil	Oculomotor (III)
Iris (circular muscles)	Parasympathetic stimulation; contraction of pupil	Oculomotor (III)

Next to the sclera is the middle layer of tissue called the choroid. This layer is continuous with the ciliary body and the iris. These vascular structures supply the tissues of the eye with oxygen and nutrients. Anteriorly, the choroid joins the ciliary body, which contains ciliary muscles used to focus the lens of the eye. The ciliary processes in the ciliary body secrete aqueous humor, the fluid found in the anterior portion of the eye. The ciliary body is connected by suspensory ligaments to the biconvex, transparent lens of the eye. Contraction of the ciliary muscles causes the suspensory ligaments to relax. The lens then bulges, allowing the focusing that is necessary for close vision.

Also attached to the ciliary body is the iris, or colored portion of the eye, which helps regulate the amount of light entering the eye. In a brightly lit environment, the iris contracts, causing the opening in the center of the iris, the pupil, to become smaller. In limited light conditions, the iris relaxes and the pupil enlarges, permitting more light to enter the eye.

The innermost layer, covering the posterior three quarters of the eye, is called the retina. The retina is a light-sensitive layer made up of photo-receptive cells called rods and cones. The rods function best in dim light, thereby enabling night vision, whereas the cones function in bright light and also detect color and fine detail. Within the rods and cones, the image initiates a chemical reaction and sends messages through the nerve fiber layer of the retina to the optic nerve. The optic nerve penetrates the fibrous layers at the optic disc and continues on to the brain. The optic disc contains no receptor cells and often is called the “blind spot” of the eye. The optic nerve transmits the image to the portion of the brain that is used for vision. The brain interprets the impulses from each eye and produces a single three-dimensional image. The macula lutea, a yellow spot, lies lateral to the optic disc. In the center of the macula lutea is the fovea centralis, the area that produces the sharpest image.

Covering the anterior externally visible portion of the sclera is a thin transparent membrane called the conjunctiva. It begins at the edge of the cornea, extends over the exposed sclera, and folds anteriorly to line the inside portion of the lids. This creates both a superior cul-de-sac and an inferior cul-de-sac where the conjunctiva reflects from the sclerae to the lids. The space between the iris, the colored portion of the eye, and the anterior clear cornea is called the anterior chamber. The fluid occupying the anterior chamber is a watery substance called the aqueous humor, which is produced by the ciliary body. The fluid exits the anterior chamber through the trabecular network, a drainage system located at the junction of the base of the iris and the cornea. Appropriate pressure within the eye is maintained by the aqueous humor, which ultimately enters the general circulation of the body. The large cavity behind the lens is the vitreous body; it contains a jellylike fluid called the vitreous humor, which helps maintain the globular shape of the eyeball.

The internal lens of the eye is elastic and therefore can focus images whether viewed close by or at a distance. The focusing is accomplished by contraction and relaxation of the muscles of the ciliary body. This action makes it possible for the lens to assume either a more rounded spherical shape or a flatter elongated shape, depending on the focus length required. The lens is attached to the ciliary body by small strands of tissue called zonules. These are attached at points all the way around the lens. When the ciliary body relaxes, the zonules are pulled, causing a flattening of the lens, the configuration needed for focusing on a distant image.

Light rays are the key to sight. The light rays enter the eye and pass through the cornea, aqueous humor, lens, and finally the vitreous humor. These rays can travel in a straight line or be bent at an angle. The process of bending light rays is known as refraction. The cornea and lens are capable of bending or refracting the light rays so that they can be focused on the retina. The image that forms on the retina is reversed both in the up/down and right/left directions. The image is turned right side up and forward in the brain as the brain interprets the visual concept. Another step in the process of vision involves accommodation. Adjustments must be made in the eye to facilitate the image in relation to the viewer’s distance from the object. The process of accommodation involves changing the shape of the lens, making it either flatter or thicker. The ciliary muscle and the suspensory ligaments contract and relax in opposition to accomplish this task.

The intrinsic muscles of each eye respond to light levels and change the size of the pupil to regulate the amount of light that enters the eye and reaches the retina. Each eye has six extrinsic muscles that control the movements of the eye; these muscles pull on the eyeballs, making the two move together to converge on one visual field (see Table 5-1). Normally, the eyes work together in unison, so an assessment of the functioning of these muscles often is included in a neurologic assessment. Table 5-2 summarizes the functions of the major parts of the eye.

TABLE 5-2

Functions of the Major Parts of the Eye

STRUCTURE	FUNCTION
Sclera	External protection
Cornea	Light refraction
Choroid	Blood supply
Iris	Light absorption and regulation of pupillary width
Ciliary body	Secretion of vitreous fluid; in addition, its smooth muscles change the shape of the lens
Lens	Light refraction
Retinal layer	Light receptor that transforms optic signals into nerve impulses
Rods	Means of distinguishing light from dark and perceiving shape and movement
Cones	Color vision
Central fovea	Area of sharpest vision
Macula lutea	Blind spot
External ocular muscles	Movement of the globe
Optic nerve (cranial nerve II)	Transmission of visual information to the brain
Lacrimal glands	Secretion of tears
Eyelid	Eye protection

Some eye disorders are signs of systemic diseases, such as hypertension, diabetes mellitus, or certain autoimmune arthritic diseases. Common symptoms of eye diseases and conditions that should be called to the attention of the physician include the following:

Redness of the eye

• Pain, itching, or burning in or around the eye

• Swollen red eyelids

Drainage from the eyes

• Lesions/sores in or around the eyes

• Visual disturbances

• Unequal pupils, sudden loss of vision, persistent pain or other symptoms associated with eye injury

• Repetitive, involuntary movements of the eye

Diagnostic tests for eye diseases and conditions include the following:

• Eye charts, such as the Snellen chart, to measure visual acuity

• Visual field tests to check central and peripheral vision

• Tonometry to measure intraocular pressure

• Eye cultures to identify viral or bacterial infectious agents

• Dilation to directly view the posterior structures of the eye, including the retina and optic nerve

• Electronystagmography (ENG) to measure the direction and degree of nystagmus

• Electroretinography to measure electric activity of the retina in response to flashing of light

• Fluorescein angiography to assess the vasculature of the eye

Optical Coherence Tomography (OCT) scans to capture three-dimensional images and to measure the dimensions of structures in the posterior chamber, such as epiretinal membranes and optic discs

Many systemic medications taken for a variety of diseases can have ocular side effects. Thus it is important for patients taking certain systemic medications to be monitored periodically for ocular toxicity. These include plaquenil used in the treatment of lupus and rheumatoid arthritis, ethambutol used in the treatment of tuberculosis, and steroids used in the treatment of various conditions.

Refractive Errors

Refractive errors are the most common cause for diminished visual acuity. Refractive errors that result in the eye being unable to focus light effectively on the retina are identified as hyperopia, myopia, astigmatism, and presbyopia.

Hyperopia (Farsightedness)

Description

Hyperopia (farsightedness) occurs when light that enters the eye is focused behind the retina rather than on the retina, which requires refocusing by the internal lens or the use of an external corrective lens to reposition the viewed object on the retina to sharpen the image. With this condition, near vision is particularly impaired. Hyperopia occurs when the eyeball is abnormally short as measured from front to back (Figure 5-2).

ICD-9-CM Code 367.0

ICD-10-CM Code H52.03 (Hypermetropia, bilateral)

(H52.00-H52.03 = 4 codes of specificity)

Myopia (Nearsightedness)

Description

Myopia (nearsightedness) is the result of light rays entering the eye being focused in front of the retina, causing blurred vision. Near objects can be seen clearly, but distant objects are blurry, and the image being viewed cannot be sharpened by the internal lens of the eye. Myopia occurs when the eyeball is abnormally long as measured from front to back (Figure 5-3).

ICD-9-CM Code 367.1

ICD-10-CM Code H52.13 (Myopia, bilateral)

(H52.10-H52.13 = 4 codes of specificity)

Astigmatism

Description

Astigmatism is an irregular focusing of the light rays entering the eye. It usually is caused by the cornea not being spherical. The front of the cornea may be more egg shaped than spherical, thereby causing light rays to be unevenly or diffusely focused across the retina. This causes some images to appear clearly defined, whereas others appear blurred.

ICD-9-CM Code 367.20 (Unspecified)

ICD-10-CM Code H52.209 (Unspecified astigmatism, unspecified eye)

(H52.20-H52.229 = 12 codes of specificity)

Refer to the physician’s diagnosis and then to the current editions of the ICD-9-CM and ICD-10-CM coding manuals to ensure the greatest specificity of pathology.

Presbyopia

Nystagmus

Description

Nystagmus is involuntary, repetitive, rhythmic movements of one or both eyes.

ICD-9-CM Code 379.50 (Unspecified)

ICD-10-CM Code H55.00 (Unspecified nystagmus)

(H55.00-H55.09 = 6 codes of specificity)

Refer to the physician’s diagnosis and then to the current editions of the ICD-9-CM and ICD-10-CM coding manuals to ensure the greatest specificity of pathology.

Symptoms and Signs

Any repetitive or involuntary movement of one or both eyes is a sign of nystagmus. The eye movements can be horizontal, vertical, circular, or a combination of these. Blurred or decreased vision also can be associated with nystagmus.

Patient Screening

Schedule a comprehensive ophthalmic examination for a patient complaining of changes in visual acuity or of any involuntary or “jerky” movements of the eye. Acquired nystagmus always necessitates a complete neurologic evaluation.

Etiology

Brain tumors and cerebrovascular lesions can cause nystagmus. Acquired nystagmus results when a disease process produces lesions in the brain or inner ear. Alcohol use and abuse of certain drugs also may cause this condition. Congenital nystagmus is manifested before 6 months to 1 year of age and is the most common type. Nystagmus is not necessarily associated with brain lesions and may instead be the result of abnormal development of the nervous system.

Diagnosis

Nystagmus usually can be diagnosed clinically by external examination of the eyes and observation of any involuntary movements. Other, more specific, complex tests are available as well when needed for definitive diagnosis.

Treatment

Acquired nystagmus is managed by treating the underlying cause of the condition. Congenital nystagmus often can be lessened by using the Kestenbaum procedure in which the eyes are surgically rotated towards the null point of the eye.

Prognosis

The outcome of acquired nystagmus depends on the treatment of the underlying cause. Surgical intervention for congenital nystagmus attempts to minimize nystagmus when the eyes are looking straight ahead.

Prevention

No specific method of prevention is known.

Patient Teaching

In acquired nystagmus, the patient benefits from understanding the underlying cause and treatment of the nystagmus. Parents of the child with congenital nystagmus are given support and clear explanations about the condition and the surgical treatment, if indicated.

Strabismus

Description

Strabismus, a visual defect of misalignment, is failure of the eyes to look in the same direction at the same time, which primarily occurs because of weakness in the nerves stimulating the muscles that control the position of the eyes (Figure 5-4).

FIGURE 5–4 Strabismus. (From Zitelli BJ, Davis HW: Atlas of pediatric physical diagnosis, ed 5, Philadelphia, 2008, Mosby.)

ICD-9-CM Code 378.9

ICD-10-CM Code H51.9 (Unspecified disorder of binocular movement)

(H51.0-H51.9 = 9 codes of specificity)

Refer to the physician’s diagnosis and then to the current editions of the ICD-9-CM and ICD-10-CM coding manuals to ensure the greatest specificity of pathology.

Symptoms and Signs

In esotropia (convergent strabismus, or cross-eye), both eyes turn inward; in exotropia (divergent strabismus, or wall-eye), both eyes turn outward. With either form, the main symptom is diplopia if strabismus is acquired as an adult. Diplopia is usually not present when the strabismus is congenital.

Patient Screening

Schedule a comprehensive ophthalmic examination for a patient complaining of changes in visual acuity, clearness or sharpness of visual perception, or double vision. Parents may report the noted appearance of “crossed eyes” in an infant or young child.

Etiology

Esotropia usually develops in infancy or early childhood and may be associated with amblyopia. Amblyopia is reversible until the visual pathways fully develop at about 7 to 8 years of age. In almost all cases, esotropia that develops in adults is caused by a condition or disease elsewhere in the body. Either the brain, cranial nerves, or the muscles themselves are affected. These diseases and conditions include diabetes mellitus, temporal arteritis, muscular dystrophy, high blood pressure, trauma, aneurysm, or an intracranial lesion.

Diagnosis

To discover the underlying cause, the physician performs a complete ophthalmic examination and orders various appropriate radiographic studies and blood tests.

Treatment

Strabismus should be treated as soon as possible. Early intervention is the key. Corrective glasses, treatment to minimize or prevent amblyopia, or surgery to restore the eye muscle balance may be used in the course of the treatment. In some cases preventing amblyopia involves covering the fixing eye in order to force a child to use the deviating eye.

Prognosis

In most cases children respond well to early treatment. The prognosis of adults with acquired strabismus depends upon the underlying cause.

Prevention

No specific method of prevention is known. Normal development of visual pathways begins in early childhood with appropriate retinal stimulation. Amblyopia may be prevented or at least minimized by early diagnosis and intervention.

Patient Teaching

Give parents of children with strabismus an explanation of the condition and the cause if known. Parents are taught how to apply an eye patch. Reinforce the importance of early treatment to help prevent visual loss. The adult with acquired strabismus can benefit from an explanation of the relationship of the eye condition to the identified underlying cause.

Disorders of the Eyelid

Hordeolum (Stye)

Description

Hordeolum (styes) are acute, focal inflammatory infections of the sebaceous glands of the eyelids (Figure 5-5).

FIGURE 5–5 Acute hordeolum of upper eyelid. (From Seidel HM et al: Mosby’s guide to physical examination, ed 7, St Louis, 2011, Mosby.)

ICD-9-CM Code 373.11 (Hordeolum externum)

373.12 (Hordeolum internum)

373.13 (Abscess of the eyelid)

ICD-10-CM Code H00.019 (Hordeolum externum unspecified eye, unspecified eyelid)

(H00.011-H00.029 = 14 codes of specificity)

H00.029 (Hordeolum internum unspecified eye, unspecified eyelid)

H00.039 (Abscess of eyelid unspecified eye, unspecified eyelid)

(H00.031-H00.039 = 7 codes of specificity)

Symptoms and Signs

Styes occur most often at the outside edge of the lid. Pain, swelling, redness, and the formation of pus at the site are the main symptoms of a stye. Patients may report a feeling of having “something in the eye.”

Patient Screening

Patients complaining of a lesion of the eyelid, with or without purulent drainage, require an appointment with their health care provider for an examination of the affected area. Follow office policy for referral to an ophthalmologist.

Etiology

Often styes are the result of a staphylococcal infection and can be associated with and secondary to blepharitis (see “Blepharitis” section).

Diagnosis

Visual examination alone is usually sufficient for making the diagnosis.

Treatment

To hasten drainage, warm compresses over a period of days may be applied to the eye as soon as the inflammation is evident. Topical antibiotics are also effective at shortening the duration of symptoms. If surrounding soft tissue becomes infected (cellulitis), oral antibiotics may be needed. If persistent, these lesions need to be surgically drained.

Prognosis

The hordeola are usually self-limiting infections, thus the prognosis is good but recurrence can be common.

Prevention

Lid hygiene and warm compresses can prevent recurrence.

Patient Teaching

Instruct the patient regarding the correct technique of applying an eye compress as prescribed. Inform the patient concerning the correct application and usage of topical or systemic antibiotic therapies.

Chalazion

Description

A chalazion is a small, firm, nonmobile, painless, subcutaneous nodule on the margin or body of the eyelid; it occurs with occlusion of the meibomian glands.

ICD-9-CM Code 373.2

ICD-10-CM Code H00.19 (Chalazion unspecified eye, unspecified eyelid)

(H00.00-H00.19 = 7 codes of specificity)

Symptoms and Signs

A chalazion can vary in size from being barely visible to being the size of a pea. Chalazia can become infected, producing redness, swelling, and pain. (Figure 5-6)

FIGURE 5–6 Chalazion. (From Zitelli BJ, Davis HW: Atlas of pediatric physical diagnosis, ed 5, Philadelphia, 2008, Mosby.)

Patient Screening

A brief visual examination by an ophthalmologist is sufficient for the diagnosis of a chalazion.

Etiology

Chalazia are caused by a blockage of fluid originating from one of the meibomian glands, which lubricate the eyelid margin.

Diagnosis

Visual examination and patient history are all that is necessary to make the diagnosis.

Treatment

Small chalazia usually disappear spontaneously over a month or two with the regular application of warm compresses. Resolution may be facilitated by topical antibiotic treatment. Antibiotic therapy may vary from gentamycin or tobramycin to azithromycin or quinolone drops.

Isolated recurrent chalazia may respond to corticosteroid injection. Larger chalazia may not spontaneously disappear and may need to be removed surgically. This is a minor procedure that often can be done in the ophthalmologist’s office in an outpatient setting.

Prognosis

Complete resolution is expected, but chalazia can be recurrent.

Prevention

Lid hygiene and warm compresses can help prevent recurrence.

Patient Teaching

The patient may be told a chalazion is not infectious. If surgical removal is recommended, reassure the patient that the procedure is minor.

Keratitis

Description

Keratitis is any inflammation or infection of the cornea.

ICD-9-CM Code 370

ICD-10-CM Code H16.9 (Unspecified keratitis)

Keratitis has many forms and therefore many ICD-9-CM and ICD-10-CM codes. Refer to the physician’s diagnosis and then to the current editions of the ICD-9-CM and ICD-10-CM coding manuals to ensure the greatest specificity of pathology.

Symptoms and Signs

Symptoms are decreased visual acuity, irritation, tearing, photophobia, and mild redness of the conjunctiva. Pain or numbness of the cornea may soon follow and is a significant sign.

Patient Screening

The patient experiencing the symptoms listed above is scheduled for a prompt ophthalmic examination. Follow office policy for referral to an ophthalmologist.

Etiology

Keratitis often is caused by an infection resulting from the herpes simplex virus. This is especially likely when the keratitis is preceded by an upper respiratory infection (URI) with facial cold sores (see “Herpes Simplex [Cold Sores]” section in Chapter 8). Certain bacteria and fungi also can be responsible for keratitis. Contact lens wear substantially increases the risk of bacterial keratitis, especially for those who sleep with lenses in place. Other forms of keratitis can be caused by corneal trauma, or exposure of the cornea to dry air or intense light, as occurs during welding. Cultures may be taken to identify the causative organism.

Diagnosis

Examination of the cornea using a slit lamp confirms the diagnosis. Medical history may indicate a recent URI, and visual acuity may be decreased.

Treatment

Ophthalmic moisturizing ointments and eye drops may be prescribed for symptomatic relief. The administration of a broad-spectrum antibiotic or an antiviral agent can effectively eradicate the infection, depending on which type of organism is the causative agent. An eye patch may be needed to relieve discomfort caused by photophobia. However, this is contraindicated in cases of fungal infection or contact lens wear.

Prognosis

Prompt treatment of the condition decreases the risk of ulceration that can erode the cornea and cause formation of scar tissue that may interfere with vision.

Prevention

Following the recommended instructions for contact lens wear and care, such as proper handling and cleaning of the lenses, can reduce the risk of infection. Avoiding hand to eye contact can lessen transfer of infection to the eye from contaminated medication, makeup, or contact lenses.

Patient Teaching

Explain how infections can be transferred to the eyes by the fingers. Encourage contact lens wearers to adhere to strict hand hygiene. Teach the patient the proper technique for instillation of ophthalmic ointment and eye drops as prescribed; emphasize the importance of proper hand washing. Inform the patient of the increased risk of keratitis with wearing contact lenses while sleeping.

Blepharitis

Description

Blepharitis is inflammation of the margins of the eyelids involving hair follicles and glands.

ICD-9-CM Code 373.00 (Unspecified)

373.01 (Ulcerative blepharitis)

373.02 (Squamous blepharitis)

ICD-10-CM Code H01.009 (Unspecified blepharitis unspecified eye, unspecified eyelid)

(H01.001-H01.029 = 21 codes of specificity)

H01.019 (Ulcerative blepharitis unspecified eye, unspecified eyelid)

H01.029 (Squamous blepharitis unspecified eye, unspecified eyelid)

Refer to the physician’s diagnosis and then to the current editions of the ICD-9-CM and ICD-10-CM coding manuals to ensure the greatest specificity of pathology.

Blepharitis causes persistent redness and crusting on and around the eyelids (Figure 5-7). Symptoms may include itching, burning, or a foreign body sensation. In severe cases, eyelashes can fall out, and the patient may experience persistent irritation of the eyes.