Lesson 1, Topic 1
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Eye Diseases and Disorders

April 11, 2024

Eye Diseases and Disorders

Learning Objective: Examine the diseases and disorders of the eye, including the signs, symptoms, etiology, diagnostic procedures and treatments.

The following sections discuss the common diseases and disorders of the eye, including the signs, symptoms, etiology, diagnostic procedures, and treatments.

Refractive Errors

Learning Objective: Discuss refractive errors, including the signs, symptoms, etiology, diagnostic procedures, and treatments.

Four major types of refractive errors result when the eye is unable to focus light effectively on the retina. Refraction is the ability of the lens of the eye to bend parallel light rays coming into the eye so that the rays are focused simultaneously on the retina. An error of refraction means that the light rays are not refracted or bent properly and consequently do not focus correctly on the retina. Defects in the shape of the eyeball can cause a refractive error. Most refractive errors can be corrected with corrective lenses, contacts, or surgery (Figure 16.4).

Hyperopia (Farsightedness)

When light enters the eye and focuses behind the retina, a person has hyperopia. This disorder occurs when the eyeball is too short from the anterior to the posterior wall. An individual with hyperopia has difficulty seeing objects that are close, at reading or working level. A convex corrective lens helps the eye’s internal lens place objects directly on the retina and creates a sharp, detailed image, or refractive surgery may be done to correct the shape of the lens.

Myopia (Nearsightedness)

Myopia occurs when light rays entering the eye focus in front of the retina, causing objects at a distance to appear blurry and dull. Objects viewed at reading or working level are seen clearly. This disorder causes the eyeball to become elongated from the anterior to the posterior wall, and images cannot be sharpened by the internal lens of the eye. A concave corrective lens is used to focus the light rays on the retina, or surgery can be done to change the shape of the cornea. However, the surgery is performed only on adults who have had a stable eye prescription for at least 1 year.

FIGURE 16.4  Errors in refraction. (A) Myopia. (B) Hyperopia.

Presbyopia

As people age, the lens of the eye becomes less flexible, and the ciliary muscles weaken; consequently, changing the point of focus from distant to near becomes difficult. This is called presbyopia. The condition results in difficulty seeing at reading level. A combination corrective lens, known as a bifocal lens or progressive lens correction, is used to focus both distal and proximal objects directly on the retina. Presbyopia actually starts at approximately age 10, but most people do not report an alteration in vision until their early 40s. Conductive keratoplasty is a laser surgical procedure used to treat presbyopia.

Astigmatism

Astigmatism occurs when light rays entering the eye are focused irregularly. This usually occurs because the cornea or the lens is not a smooth sphere but rather has an irregular shape. Ophthalmologists describe the lens as being shaped like a football rather than a sphere, such as a basketball. This causes light rays to be unevenly or diffusely focused on the retina, resulting in blurred vision. It is like attempting to focus on objects seen through a wavy piece of window glass. Astigmatism can be corrected with glasses, contacts, or surgery. Surgical correction attempts to reshape the cornea into a more spherical or uniformly curved surface.

Signs and Symptoms of Refractive Errors

Refractive errors in vision can lead to squinting, frequent rubbing of the eyes, and headaches. The individual notices blurred vision, fading of words at reading level, or both. Some refractive errors are familial in nature.

Treatment of Refractive Errors

Eyeglasses and contact lenses are the traditional treatments for visual acuity problems caused by refractive errors. However, problems with the shape of the lens can be corrected surgically. Surgery is performed on an outpatient basis and requires only a short stay in the facility. Medical assistants employed in an outpatient eye surgery facility must be trained to fulfill this specialized role.

Surgical Correction of Refractive Errors

Most types of health insurance do not cover surgery for refractive corrections. On average, each eye costs $1500 to $3000. The following are some of the surgical procedures performed to correct refractive errors:

• Photorefractive keratectomy (PRK): The first surgical procedure developed to reshape the cornea with a laser. The same type of laser is used for PRK and LASIK. The major difference between the two types of surgery is how the middle layer of the cornea is exposed before it is vaporized with the laser. In PRK, the top layer of the cornea (the epithelium) is scraped away to expose the stromal layer underneath. In LASIK, a flap is cut in the stromal layer.
• Laser-assisted in situ keratomileusis (LASIK): LASIK uses an excimer laser to reshape the central cornea to treat myopia, hyperopia, and astigmatism. A thin, hinged flap of the cornea is created, the flap is lifted, and the exposed surface of the cornea is reshaped. After the corneal curvature has been corrected, the flap is replaced, and the area heals without stitches.
• Laser-assisted epithelium keratomileusis (LASEK): In LASEK surgery, the surface epithelial cells of the eye are softened with an alcohol solution, allowing the epithelial layer to be rolled back and the cornea to be exposed. A laser is then used to reshape the cornea and treat myopia, hyperopia, and astigmatism. The epithelial flap is returned to its original position, and a contact lens is placed on the cornea as a bandage for several days to aid healing and reduce pain.
• Conductive keratoplasty (CK): CK uses heat created by a laser to reshape the cornea. Heat is applied to the cornea’s outer edge to tighten and steepen the cornea. CK is used in patients older than 40 years of age who need correction for hyperopia, presbyopia, and myopia. The procedure causes little or no discomfort and improves vision almost instantly. The corneal changes are not permanent, and retreatment may be required.

16.2

Critical Thinking Application

Amy is assisting Dr. Martin with visual acuity examinations. He asks her whether she understands the causes of refractive errors. Amy has difficulty explaining why refractive errors occur, so she tells Dr. Martin she will research the topic and get back to him. What have you learned about the different refractive disorders and why they occur?

Strabismus

Learning Objective: Discuss strabismus, including the signs, symptoms, etiology, diagnostic procedures, and treatments

Strabismus is failure of the eyes to track together, which means that both eyes do not look in the same direction at the same time. Adults can develop strabismus because of a condition or disease elsewhere in the body, such as diabetes mellitus, muscular dystrophy, or hypertension, or as the result of a head injury. In children, strabismus is caused by weakness in the muscles that control eye movement. If the condition appears in infancy or childhood, it is most commonly associated with amblyopia. Treatment involves having the child wear a patch over the unaffected eye so that the muscles of the “lazy” eye are strengthened or administering atropine eyedrops to the unaffected eye to medically decrease visual acuity in the “sound” eye, thereby forcing the amblyopic eye to compensate. It was once standard therapy that an eye patch would be worn up to 6 hours per day, but getting young children to comply with this treatment is very challenging. In children with moderate amblyopia, research shows that patching daily for 2 hours is as effective as patching for 6 hours daily, and daily atropine is as effective as daily patching. Children older than 7 years may still benefit from patching or atropine, particularly if they have not previously received treatment for amblyopia. Amblyopia recurs in 25% of children after patching is discontinued; however, slowly reducing the amount of time the patch is worn each day at the end of treatment reduces the risk of recurrence. The main symptom in all age groups is diplopia (double vision).

Nystagmus

Learning Objective: Discuss nystagmus, including the signs, symptoms, etiology, diagnostic procedures, and treatments.

A constant, involuntary movement of one or both eyes are called nystagmus. The eye can move in any direction, and the movement is accompanied by blurred vision. A child may be born with the problem (congenital nystagmus), or the condition may be acquired as a result of a brain tumor, an inner ear lesion, multiple sclerosis, or substance abuse. Nystagmus is caused by an abnormal function in the part of the brain that controls eye movements. Congenital nystagmus is more common than acquired nystagmus, is usually milder, does not worsen over time, and is not associated with any other disorder. A patient with signs and symptoms of nystagmus should initially have a neurologic evaluation to determine the cause of the disorder, with treatment based on those findings. However, congenital nystagmus has no cure. Affected individuals typically are not aware of the eye movements, but they may have a decrease in visual acuity that can be corrected with surgery or corrective lenses.

Infections of the Eye

Learning Objective: Discuss infections of the eye, including the signs, symptoms, etiology, diagnostic procedures, and treatments.

Many acute disorders of the eye are seen in the ophthalmologist’s office. These include the following:

• Hordeolum (sty): A localized, purulent infection of a sebaceous gland of the eyelid. The area is inflamed, swollen, and painful. The infection usually is caused by staphylococci, and it is treated with warm compresses and topical or systemic antibiotics.
• Chalazion: A small cyst that results from blockage of a meibomian gland (sebaceous gland) and lubricates the posterior margin of each eyelid. The cyst can become infected, inflamed, swollen, and painful. It may disappear spontaneously or may need to be removed surgically.
• Keratitis: Inflammation of the cornea that results in superficial ulcerations. It can be caused by the herpes simplex virus, bacteria, or fungi, or it may develop as a result of corneal trauma (e.g., intense light). Symptoms include inflammation, tearing, pain, and photophobia. The condition is treated with ophthalmic ointments, eye drops, and use of an eye patch.
• Conjunctivitis: Inflammation of the conjunctiva caused by irritation, allergy, or bacterial infection. Bacterial conjunctivitis (pinkeye) is highly contagious and produces a purulent discharge. Symptoms include inflammation, swelling and itching of the sclera, photophobia, and tearing. Bacterial infections are treated with antibiotic ophthalmic preparations.
• Blepharitis: Inflammation of the glands and lash follicles along the margins of the eyelids that may be caused by staphylococcal infection, allergies, or irritation. Symptoms include itching and inflammation along the eyelash margins; the condition is treated with antibiotic ophthalmic ointment.

Disorders of the Eyeball

Learning Objective: Discuss disorders of the eyeball, including the signs, symptoms, etiology, diagnostic procedures, and treatments.

The following sections discuss the common disorders of the eyeball, including the signs, symptoms, etiology, diagnostic procedures, and treatments.

Corneal Abrasion

The cornea, the transparent outer covering of the eye, is prone to abrasion because of its location. Symptoms of corneal abrasion include pain, inflammation, tearing, and photophobia. The abrasion is usually caused by a foreign body in the eye or by direct trauma, such as from poorly fitting or dirty contact lenses. A corneal ulcer may form and become infected.
Diagnosis is based on the patient’s signs and symptoms, but it can be confirmed with the instillation of fluorescein stain (Figure 16.5). After instillation of the stain, the provider uses a cobalt blue filtered light to visualize the abrasion, which appears green (Figure 16.6). If the abrasion is caused by a foreign body, it must be removed first; the eye can then be treated with antibiotic ophthalmic ointment to prevent infection. Although patching the affected eye has been recommended in the past, studies now show that patching does not reduce the patient’s pain and may actually prolong healing time. Corneal abrasions are quite painful, so the patient may be prescribed topical nonsteroidal anti-inflammatory ophthalmic drops, such as diclofenac (Voltaren) and ketorolac tromethamine (Acular), in addition to oral analgesics. Most corneal abrasions heal in 24 to 72 hours, but the patient should be aware that symptoms can worsen if the affected eye is exposed to bright light, if excessive blinking occurs, or if the patient rubs the injured surface of the cornea against the inside of the eyelid. Because the patient may develop a secondary infection from the corneal injury, topical antibiotics, including ciprofloxacin 0.3% (Ciloxan) ointment or drops and gentamicin 0.3% ointment or drops may be prescribed. Patients with contact lenses may be prescribed oral antibiotics and should not wear their contacts until the abrasion has healed and the course of antibiotics has been completed.

FIGURE 16.5  Corneal abrasion stained with fluorescein.

FIGURE 16.6  Corneal abrasion stained with fluorescein and highlighted by cobalt blue light.

FIGURE 16.7  Cataract. From Black JM, Hawks JH, Keene A: Medical surgical nursing: clinical management for positive outcomes, ed 8, Philadelphia, 2009, Saunders.

Cataract

A cataract is a cloudy or opaque area in the normally clear lens of the eye that blocks the passage of light into the retina, causing impaired vision. This condition may result from injury to the eye, exposure to extreme heat or radiation, or inherited factors. However, most cataracts develop slowly and progressively as a result of the natural aging deterioration of the lens of the eye and typically occur after age 60. With advanced cataracts, the pupil of the eye appears white or gray (Figure 16.7).
A cataract scatters the light as it passes through the lens, preventing a sharply defined image from reaching the retina resulting in blurred and dimmed vision. The patient may need a brighter reading light or must hold objects closer to the eyes for better viewing. Continued clouding of the lens may cause diplopia. The patient also needs frequent changes of eyeglass prescriptions. Patients with cataracts report difficulty with night vision (nyctalopia), seeing halo images around lights, and increased sensitivity to glare. If left untreated, cataracts ultimately can lead to blindness.
When the patient’s vision becomes distorted or appears to be deteriorating, the ophthalmologist performs a slit lamp procedure, in which the structures at the front of the eye are examined using a combination of a low-power microscope and a high-intensity light that shines into the eye as a slit beam.
The symptoms of early cataracts may be improved with new eyeglasses, brighter lighting, and antiglare sunglasses. If these measures do not help, surgical removal of the lens is the only effective treatment. This is performed as an outpatient procedure in a clinic or hospital. After the eye has been anesthetized, the inner portions of the lens (the nucleus and the cortex) are removed. The provider may use an extracapsular extraction, in which the cataract is removed in one piece, or phacoemulsification, in which an ultrasonic probe is used to break up the cataract and the pieces are aspirated before an artificial intraocular lens (IOL) is implanted. The incision may be closed with fine sutures, or it may be sutureless and self-sealing. The procedure usually takes 15 minutes, and the patient typically can leave the facility after 1 hour. Patients should be aware that they will not be able to drive until cleared by the ophthalmologist and that they may need help at home until their vision is clear.
The patient is seen in the office the day after surgery and as frequently as needed for the next month. Vision gradually improves until it stabilizes, usually within 2 to 6 weeks; the patient then is fitted with new corrective lenses to match the improved vision.

Glaucoma

Learning Objective: Discuss glaucoma, including the signs, symptoms, etiology, diagnostic procedures, and treatments.

One of the most common and serious ocular disorders is a group of diseases known as glaucoma. Glaucoma is characterized by increased intraocular pressure (IOP), which damages the optic nerve and causes blindness if left untreated. It rarely occurs in people younger than age 40 and usually is seen in individuals older than age 60. The cause is unknown, but a hereditary tendency toward development of the most common forms has been noted. Glaucoma is responsible for approximately 12% of all cases of blindness. After cataracts (which are typically age related and can be resolved surgically), glaucoma is the leading cause of blindness among African Americans. It is estimated that more than 3 million Americans have glaucoma, but only half of those know they have it.
The ciliary body constantly produces aqueous humor, which should circulate freely between the anterior and posterior chambers of the eye and eventually empty into the general circulation. A healthy eye is filled with fluid in an amount carefully regulated to maintain the shape of the eyeball. In chronic open-angle glaucoma, the channels that drain the fluid malfunction, and over time aqueous humor builds up, resulting in increased pressure, which affects the blood supply to the retina and the optic nerve. With acute closed-angle glaucoma, the opening of the drainage system narrows or closes completely, causing a sudden increase in IOP.
Patients can have chronic open-angle glaucoma for a long time before symptoms occur. Early detection through regular ophthalmic examinations that include IOP measurements is crucial to prevent permanent vision loss. The need to change eyeglass prescriptions frequently, loss of peripheral vision (often called “tunnel vision”), mild headaches, and impaired adaptation to the dark are some of the signs and symptoms that may be seen with chronic glaucoma. Acute closed-angle glaucoma has more obvious symptoms; the patient complains of severe pain, headaches, inflammation, photophobia, and seeing halos around lights. If left untreated, acute glaucoma can cause permanent blindness in a matter of days.
Screening for glaucoma is conducted during a complete eye examination. The ophthalmologist first uses a tonometer with a slit lamp to measure IOP. The air puff tonometer records the degree of indentation of the cornea from a puff of pressurized air without touching the eye. An applanation tonometer records the pressure needed to indent the cornea when the instrument is applied to the front surface of the eye. Electronic tonometry is the most recently developed technique. The ophthalmologist gently places the rounded tip of a tool that looks like a pen directly on the cornea, with results evident on a small computer panel. Gonioscopy can also be used to examine the aqueous fluid drainage system and determine whether the glaucoma is the open- or closed-angle type. In addition, an ophthalmoscopic examination can identify cupping of the optic disc, which indicates atrophy of the optic nerve.
Diagnosis and immediate treatment for early-stage, open-angle glaucoma can delay the progression of the disease. Open-angle glaucoma can be relieved with miotic and beta-blocker eye drops. The combinations of drugs used to treat glaucoma can vary considerably. Miotic medications increase the outflow of aqueous humor, and beta-blockers reduce the production of aqueous humor. It is imperative that the patient use prescribed eye drops and take oral medications daily to prevent further damage to the optic nerve. Laser surgery may be performed to create an opening or build a new channel for drainage of the aqueous humor. The goal of treatment in any type of glaucoma is to diagnose the disease early and effectively treat its progression because any loss of sight that has occurred as the result of increased IOP cannot be regained. In closed-angle glaucoma, medications to lower IOP are prescribed so that surgery can be performed to create a channel in which aqueous fluid can circulate. This is a medical emergency because the pressure must be relieved within a few hours or permanent vision damage occurs.

Diabetic Retinopathy

Learning Objective: Discuss diabetic retinopathy, including the signs, symptoms, etiology, diagnostic procedures, and treatments.

Diabetic retinopathy is a complication of diabetes mellitus. The blood vessels of the retina become damaged from hyperglycemia, causing blockages in the small blood vessels and a decrease in the blood flow to the retina. New blood vessels form but don’t develop properly and can leak easily. In the early stages of the disease, there are not many symptoms, but over time the patient may develop spots or dark strings floating in their vision, blurred or fluctuating vision, dark or empty areas in their vision, and vision loss. A comprehensive eye examination can diagnose diabetic retinopathy. Fluorescein angiography and optical coherence tomography may also be used. Treatment is focused on slowing or stopping the progression of the disease. For advanced diabetic retinopathy injection of endothelial growth factor inhibitors can be done to decrease the fluid buildup and to help stop the growth of new blood vessels. Photocoagulation, a laser treatment, can be done to slow or stop the leakage of blood and fluid in the eye. Another type of laser treatment, panretinal photocoagulation, also known as scatter laser treatment, can shrink the vessels. Vitrectomy, a tiny incision in the eye, can be done to remove blood from the middle of the eye and scar tissue.

Macular Degeneration

Learning Objective: Discuss macular degeneration, including the signs, symptoms, etiology, diagnostic procedures, and treatments.

The macula lutea, the part of the retina near the optic nerve, defines the center of the field of vision. Macular degeneration is a progressive deterioration of the macula lutea, which causes loss of central vision; the patient can see only the edges of the visual field (Figure 16.8). The condition affects more than 11 million Americans and is a leading cause of blindness in those older than 50.

FIGURE 16.8  Visual field for a patient with macular degeneration. From the National Eye Institute: Age-related macular degeneration: what you should know, National Institutes of Health, Bethesda, MD.

Two types of macular degeneration can occur. The dry form accounts for most cases; it is painless and develops slowly, affecting sharp vision over time so that reading and other activities that require fine, detailed vision become impossible. Wet macular degeneration causes 90% of all severe vision losses from the disease and has an acute onset and rapid progression. Dry macular degeneration is caused by the breakdown of light-sensitive cells in the region of the macula; the wet form is seen when new blood vessels behind the retina form and leak blood and fluid into the macula. The condition is age related, but additional risk factors include cigarette smoking, obesity, family history, cardiovascular disease, elevated blood cholesterol levels, light eye color, and excessive sun exposure. The disease has no known cure, but research indicates that antioxidants, including beta carotene and vitamins C and E with zinc and copper, may prevent the condition or help treat the disease in people who have intermediate macular degeneration.