Major ocular disorders: cataracts, glaucoma, and retinal disease

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.

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

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

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

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 31.8). The condition affects more than 11 million Americans and is a leading cause of blindness in those older than 50.

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.