Advances in Diagnosis and Treatment of Diseases of the Eye

Overview

Major innovations in diagnosis and treatment of diseases of the eye occurred in the last half of the twentieth century. From the development of the contact lens to precise lasers used in surgery of the eye, technology played a vital role in the correction of visual difficulties. Recent research has advanced scientific and clinical knowledge of how the eye functions, providing a basis for future sight-saving treatments.

Background

Although progress in understanding and treating diseases of the eye was significant from 1950 until the end of the century, the need for eye care increased dramatically. In the United States alone, one third of the population is estimated to need corrective lenses in order to see properly. The economic impact of visual disabilities climbed to over 35 billion dollars in 1995 in direct medical costs and indirect costs to society through lost productivity.

The National Eye Institute, created by Congress in 1968, joined with similar organizations world-wide to encourage innovations in medical technology and therapies for the treatment of eye disease. The developed world reaped most of the benefit from recent advances, as new drug therapies and surgical techniques quickly spread, fueled by consumer interest for better eyesight without eyeglasses. While patients in North America and Europe queued for voluntary high-tech surgeries, preventable blindness became a disproportionate problem in developing countries. The World Health Organization identified some diseases of the eye, such as glaucoma, as major targets for reduction in the twentieth-first century.

Impact

Prior to 1950, spectacles (eyeglasses) and the magnifying glass were the most common forms of treatment for visual problems, and impaired eyesight was considered an inevitable consequence of aging. Lenses for eyeglasses were often thick and cumbersome to wear, and their design allowed for peripheral vision distortion. Modern contact lenses, invented in 1948 by Kevin Tuohy, provided an alternative to eyeglasses. The lenses were made of hard plastic, were larger than the iris, and rested on the cornea (the transparent, curved surface of the eye) supported by a layer of tears. Contact lenses are used to treat myopia (near-sightedness), astigmatism (distorted vision due to slight irregularities in the shape of the cornea), and other refractory visual defects. Contact lenses also reduce peripheral vision distortion since the lenses move with the eye. Many considered contact lenses more cosmetically appealing than glasses, and by the mid-1960s, millions of Americans wore them—two thirds of whom were women. Corneal irritation was the main complication associated with contact lenses. During the 1970s and 1980s, improvements in the composition of the lenses reduced discomfort and irritation. Other improvements included the soft contact lenses made from water-absorbing plastics, extended-wear lenses, and gas-permeable hard lenses which allowed more oxygen to reach the eye. Tinted lenses to enhance or change eye color added to the appeal of contact lenses.

Beginning in the 1960s, modern refractive surgeries were performed on the eye to create better vision and decrease the need for wearing glasses. Russian surgeons corrected myopia by making multiple incisions on the anterior (front) surface of the cornea in a technique called Radial Keratotomy (RK). The results of RK demonstrated dramatic improvement of vision, and interest in RK quickly spread to the United States. A study sanctioned by the National Eye Institute demonstrated the initial effectiveness of RK, but also found a disturbing number of patients left with fluctuating daily vision after RK surgery. The procedure's popularity waned until the 1980s, when newly developed technologies such as microscopic guided lasers emerged. In PRK (photorefractive keratotomy), precise corneal incisions are made by laser energy which flattens the corneal surface, correcting myopia while leaving daily visual acuity stable. PRK has virtually replaced RK in the United States as the safest and most effective surgery of its kind for the correction of nearsightedness. In the 1980s and 1990s, thousands of PRK operations were performed across North America and Europe, and many PRK recipients experienced enough visual improvement to abandon their eyeglasses.

By the end of the century, the new surgical procedure Laser in Situ Keratomileusis, or LASIK, received limited approval and grew rapidly due to customer demand. LASIK involves creating a hinged flap in the cornea, and using a laser to remove minute tissue from the inside of the corneal stroma (body). The surface flap is then reattached, and the patient in most instances experiences a swift improvement in vision with less discomfort than other refractive surgeries. LASIK is used to correct myopia, hyperopia (far-sightedness), and astigmatism. LASIK surgeries were performed by the thousands by the late 1990s, just in time for the baby-boomer population to experience age-related refractory eye changes. LASIK and PRK surgeries have made it possible for thousands of people around the world to see clearly without depending on glasses or contact lenses.

Lasers were also used to treat glaucoma, a disease in which the fluid pressure inside the eye elevates, damaging the optic nerve and leading to vision loss. When medications fail to control the pressure, laser surgery is considered. By focusing many tiny laser burns to the filtering angle area of the eye, an area is created which improves fluid drainage, and pressure is reduced. Another laser surgery for glaucoma focuses on creating a small opening in the peripheral opening of the iris. This helps keep fluid from building up behind the iris, and preserves the ability of the iris to filter light. Before the advent of laser-guided microsurgery in the 1980s, those affected with glaucoma had few options to preserve sight when conventional medicines failed them.

Beginning in 1950, surgeons implanted artificial intraocular lenses in patients whose vision was clouded by cataracts. A cataract is an opacity of the normally clear lens of the eye that restricts vision. World-wide, cataracts are the cause of half of all blindness, and are the result of advancing age, trauma, genetic predisposition, or metabolic disorders. By the 1970s, the overwhelming success of new, flexible, light-weight plastic lenses created a revolution in cataract treatment in the developed world. Surgeons were able to remove the clouded lens, and select from among several therapeutic artificial lenses the one which would best minimize the patient's need for glasses after surgery. By the end of the twentieth century, an artificial lens was nearly always implanted in the eye at the time of cataract surgery, and the United States had spent more than three billion dollars on this successful procedure through the Medicare program alone.

Complications from diabetes often lead to eye disease, especially those of the retina (the inside lining of the back surface of the eye where light energy is converted into electrical impulses). Diabetic retinopathy involves tiny hemorrhages and deposits in the retina, as well as abnormal retinal blood vessel growth, all of which may lead to blindness. Surgery known as laser photocoagulation has proved effective in maintaining and sometimes partially restoring vision.

Gene replacement therapy may one day prevent vision loss by delivering healthy genes to patients with retinal degeneration. Researchers conducted studies in rodents in the 1990s to find an appropriate vector, or delivery system, capable of introducing therapeutic genetic information to retinal cells while eliminating the harmful genetic information. In gene therapy experiments, certain viruses have successfully vectored therapeutic genetic material, resulting in delayed vision loss for long periods of time. Human gene therapy trials for retinal degeneration were anticipated by researchers as the twentieth century came to an end.

The computer chip also offered hope to patients with end-stage retinal degeneration. Designed for implantation on the surface of the retina, the chip mimics photoreceptor cell function. A camera mounted on a pair of glasses transmits visual information to the chip, which in turn transmits images to the brain via the optic nerve. Although prototypes of these high-tech visual aids were manufactured and initial testing in animals began, further work is needed before humans test the retinal chip. Researchers, however, remain optimistic about the retinal chip's future to restore functional vision for those with profound vision loss as a result of retinal degeneration.

Not all of the latest vision research and treatment involves high-tech processes. Vitamin supplements were found to benefit patients suffering vision loss from retinitis pigmentosa (RP), an inherited disease which causes the progressive destruction of specialized thin, light-absorbing cells lining the back of the retina. RP typically begins with night blindness and proceeds over time to continued loss of peripheral vision. The majority of people with RP are legally blind by age 40. Studies conducted in the 1990s showed that supplements of vitamin A palmitate in certain dosages slowed the progression RP. Additionally, vitamin E supplements were found to increase the rate of degeneration. While not touted as a cure, patients with RP have enjoyed added years of functional vision due to vitamin A supplementation therapy.

Concern for protecting eye health made its way into popular culture as the twentieth century ended. Many complained of eyestrain as demands of the workplace included long hours in front of a computer screen. Studies to determine potential adverse effects were under way, and colored filters for monitors became popular items. Computer manufacturers and software companies responded by creating large, adjustable monitor screens and programs, including choices of colors intended to soothe the eyes. Sales of sunglasses touting high filtration rates of the harmful rays of the Sun soared, and were marketed for babies as well as children and adults. Safety glasses once confined to industry became fixtures in many households and were used during everyday chores such as mowing the lawn. Athletes appeared on television sporting new high-tech protective eye wear.

BRENDA WILMOTH LERNER