Myopia

Myopia, also called nearsightedness and shortsightedness, visual abnormality in which the resting eye focuses the image of a distant object at a point in front of the retina (the light-sensitive layer of tissue that lines the back and sides of the eye), resulting in a blurred image. Myopic eyes, which are usually longer than normal from front to rear, are somewhat more susceptible to retinal detachment than are normal or farsighted eyes. Severe myopia can be associated with other eye problems as well, most of which affect the retina or the choroid (i.e., pathologic blood vessel growth from the choroid).

Presbyopia

Presbyopia, loss of ability to focus the eye sharply on near objects as a result of the decreasing elasticity of the lens of the eye. The eye’s ability to focus on near and far objects—the power of accommodation—depends upon two forces, the elasticity of the lens of the eye and the action of the ciliary muscle (a roughly ring-shaped muscle that encircles the lens and is attached to it by suspensory ligaments). When the ciliary muscle is relaxed, the ring enlarges away from the lens and the suspensory ligaments are tautened, flattening the lens into a shape suitable for viewing distant objects. When the muscle contracts, the ligaments are loosened, and, because of the elasticity of the lens, the surface of the lens—particularly the front surface—becomes more curved, in keeping with viewing near objects. Ordinarily the lens gradually becomes less elastic (it hardens) with age, so the power of accommodation is lost progressively. The loss is most rapid in the decade of the 40s, the age when most people become aware of difficulty in performing a task, such as reading, that requires near focusing; this can be helped with corrective lenses.

Accommodation may also be lost temporarily as a result of paralysis of the ciliary muscle. With this paralysis, which can occur from the action of certain toxins and medications, the muscle cannot contract, and the surface of the lens is prevented from becoming more convex.

Hyperopia

Hyperopia, also called farsightedness, refractive error or abnormality in which the cornea and lens of the eye focus the image of the visual field at an imaginary point behind the retina (the light-sensitive layer of tissue lining the back and sides of the eye). The retina thus receives an unfocused image of near objects, though distant objects may be in focus. Hyperopia frequently occurs when an eye is shorter than normal from front to rear; the lens is then unable to increase its convexity sufficiently to focus the images of close objects onto the retina. Corrective lenses for hyperopia are designed to supply the additional convexity needed for focusing. Hyperopic laser in situ keratomileusis (H-LASIK) and photorefractive keratectomy for hyperopia (H-PRK) are common surgical methods that reshape the cornea to improve vision in hyperopic patients.

Macular Degeneration

Macular Degeneration, leading cause of irreversible vision loss in the United States. This incurable condition attacks the central portion of the retina, the part of the eye that receives light patterns and transmits them to the brain. Macular degeneration progressively damages or destroys the part of vision used for reading and seeing fine details, while leaving the peripheral vision generally unaffected. People who have this disorder develop an area of vision loss that increases in diameter until they are unable to read or even see groups of two to three words at normal reading distance. Macular degeneration usually develops in both eyes, with one eye generally more affected than the other.

Although children can develop forms of macular degeneration such as Stargardt's disease, 99 percent of the cases occur in older people. Age-related macular degeneration (AMD) may affect as many as 15 million Americans over the age of 50, and one-fifth of people over 75 show at least some symptoms. This article focuses on AMD, the most common form of the disease.

AMD targets the most sensitive part of the retina, a cluster of cells called the macula located directly in its center. There are two forms of AMD, dry AMD and wet AMD. In the dry form, which accounts for about 90 percent of AMD cases, the macular cells slowly waste away, causing gradual vision loss. In most cases this vision loss progresses no further than permanent blurring of the central field of vision. In the wet form, abnormal growth of blood vessels beneath the macula causes bleeding and scarring. The result is severe damage to the macula that may completely destroy the patient’s central vision.

Ophthalmologists (medical doctors with special training in diagnosing and treating eye disorders) diagnose AMD with a thorough eye exam. Visible light imaging and infrared imaging, procedures that use cameralike devices that make it easier to see abnormal blood vessels, are useful in identifying wet AMD. An ophthalmologist injects a patient with fluorescent dye that travels to the eye through blood vessels. These imaging devices snap a series of 15 to 30 pictures over a five-to ten-minute period that track the progression of dye leakage from damaged blood vessels beneath the macula.

Although the cause of AMD is still unknown, people with light-colored eyes or a family history of macular degeneration are more vulnerable to AMD. Through research on the mutated gene that causes Stargardt’s disease, scientists have discovered what they believe to be a genetic trigger for the disease. Researchers have found that 16 percent of AMD patients have alterations in this same gene. Through this growing body of research, many scientists now consider heredity to be a significant risk factor in AMD. Some evidence suggests that smokers—particularly women—and people who spend a great deal of time outdoors without eyewear that offers protection from the sun’s ultraviolet rays may have a higher rate of AMD. Hypertension also appears to increase a person’s risk of developing AMD.

No treatment is available for most cases of macular degeneration. In a small percentage of early-stage cases of wet AMD, laser surgery can seal off the leaking blood vessels to slow vision loss, but the leaks frequently recur. Medical researchers are experimenting with cellular transplants designed to replace damaged macular cells with healthy cells. New drug treatments being studied include the use of thalidomide, which slows the growth of blood vessels.

Sparse scientific evidence exists to support controversial theories that nutrition and other lifestyle factors can reduce the risk or progress of macular degeneration. However, researchers believe that vitamins A, C, and E may slow the progression of the disease.

As scientists continue to search for ways to prevent this disease or halt its progression, patients must rely on special magnifying devices that help them read and watch television. High-powered eyeglasses, handheld or mounted magnifiers, telescopes, special illumination lamps, and extra-large type are all available to AMD patients, and new devices are under development. However, people who develop this disorder generally continue to live very independent lives and can still drive if their vision complies with vision regulations for day and evening driving.

Thalidomide

Thalidomide, drug introduced in 1953, initially prescribed for its sedative properties and widely used by women to alleviate the nausea and vomiting common in the early stages of pregnancy. Thalidomide gained notoriety in 1961 when it was found to cause severe malformations in the growing fetus such as stunted development or the complete absence of limbs. More than 10,000 children were born with these disabling abnormalities before the drug was taken off the market. This disaster triggered more rigorous government regulations for drug testing. Today thalidomide is used in the treatment of leprosy, and experimentally in bone-marrow transplant patients and certain immune system disorders.

HISTORY

While its commercial distribution was halted, thalidomide continued to be used in experimental studies for a variety of diseases. A series of studies beginning in the mid-1960s showed that thalidomide was effective in treating a leprosy-related disorder, erythema nodosum leprosum (ENL). A serious skin disorder, ENL usually develops in leprosy patients after they begin taking antibiotics to combat the leprosy-causing bacterium Mycobacterium leprae. ENL is believed to be caused by an abnormal immune reaction to the killed bacteria.

The FDA approved thalidomide for the treatment of ENL in July 1998, at the same time placing unprecedented restrictions on the drug’s use. Under these restrictions, thalidomide can only be obtained from selected doctors and pharmacies that have agreed to follow a strict protocol designed to prevent birth defects from the drug. Both men and women taking the drug must use birth control during sexual intercourse, and women must also agree to undergo periodic pregnancy tests.

Thalidomide’s success in treating ENL, although not fully understood, triggered extensive studies into the drug’s effects on the immune system. Some studies suggest that thalidomide reduces the production of tumor necrosis factor-alpha (TNF-a), a protein made by immune cells that may cause problems such as wasting, or chronic weight loss, when produced in excessive amounts. Thalidomide has also been proven to heal painful canker sores in the mouth of patients with acquired immunodeficiency syndrome (AIDS) or other patients with impaired immune systems. Canker sores in these patients do not heal as readily as in people with normal immune systems, and the sores make eating difficult.

Early evidence suggests that thalidomide effectively suppresses the body’s rejection of donor bone marrow that sometimes occurs in bone-marrow transplant patients. Thalidomide is also being studied as a possible treatment for various cancers and other diseases because of its ability to inhibit growth of new blood vessels. This inhibition could slow or completely prevent growth of cancerous tumors that require new blood vessels in order to thrive.

RECENT USES

While its commercial distribution was halted, thalidomide continued to be used in experimental studies for a variety of diseases. A series of studies beginning in the mid-1960s showed that thalidomide was effective in treating a leprosy-related disorder, erythema nodosum leprosum (ENL). A serious skin disorder, ENL usually develops in leprosy patients after they begin taking antibiotics to combat the leprosy-causing bacterium Mycobacterium leprae. ENL is believed to be caused by an abnormal immune reaction to the killed bacteria.

The FDA approved thalidomide for the treatment of ENL in July 1998, at the same time placing unprecedented restrictions on the drug’s use. Under these restrictions, thalidomide can only be obtained from selected doctors and pharmacies that have agreed to follow a strict protocol designed to prevent birth defects from the drug. Both men and women taking the drug must use birth control during sexual intercourse, and women must also agree to undergo periodic pregnancy tests.

Thalidomide’s success in treating ENL, although not fully understood, triggered extensive studies into the drug’s effects on the immune system. Some studies suggest that thalidomide reduces the production of tumor necrosis factor-alpha (TNF-a), a protein made by immune cells that may cause problems such as wasting, or chronic weight loss, when produced in excessive amounts. Thalidomide has also been proven to heal painful canker sores in the mouth of patients with acquired immunodeficiency syndrome (AIDS) or other patients with impaired immune systems. Canker sores in these patients do not heal as readily as in people with normal immune systems, and the sores make eating difficult.

Early evidence suggests that thalidomide effectively suppresses the body’s rejection of donor bone marrow that sometimes occurs in bone-marrow transplant patients. Thalidomide is also being studied as a possible treatment for various cancers and other diseases because of its ability to inhibit growth of new blood vessels. This inhibition could slow or completely prevent growth of cancerous tumors that require new blood vessels in order to thrive.