The Vision Thing

What is an eye? A strange device,
A bit of film and nerve, the first camera,
A wonder steeped in mystery,
Recording scenes and filing prints in cabinets of the brain.

From “Windows of the Soul” by Grace Seaton Thompson

Our eyes are indeed a wonder, yet often taken for granted. They shouldn’t be, for eyes are vulnerable to change. From that first pair of reading glasses, often in one’s mid-40s, many of us move to full time corrective lenses, then bifocals or trifocals. “What comes next?” we may wonder.

“Eye disease is more prevalent among older persons,” says Dr. Lawrence Jaeger, of Dartmouth-Hitchcock Clinic, Keene. “As people age, there is a greater possibility of glaucoma, cataracts and macular degeneration.”

Is this the result of age, in and of itself, or the cumulative effect of stress over the years? Dr. Jaeger explains that many factors are likely to influence the health of our eyes, including genetic inheritance, the effects of UV-B light (rays that are just beyond the visible spectrum), nutrition deficits, other health problems and a history of smoking. People who are diabetic or who have abnormally high blood pressure are at greater risk for eye disease. Certain medications (steroids, for example) might accelerate glaucoma and the formation of cataracts. “We don’t know precisely the interplay of these and possibly other factors,” he says, “but research is going on all the time.”

The most prevalent eye diseases are glaucoma, macular degeneration and cataracts. In glaucoma, a buildup of fluid puts pressure on the optic nerve, which results in permanent damage to the nerve. A gene, the TIGR gene, is identified as having a role in both hereditary and non-hereditary glaucoma. This protein blocks the flow of fluid through ocular cells. Damage occurs first at the edges of the eye — affecting peripheral vision first, with a graying of visual perception. Loss of vision moves from peripheral toward central vision. Risk factors for glaucoma include age, family history, infrequent exams and race.

Damaged nerves cannot be restored. Treatment for glaucoma aims to prevent further damage by reducing pressure on the optic nerve. Several medications (eye drops) are available. Some people respond well to laser surgery, to create drainage for excess fluid. Glaucoma has been called a “silent thief of sight” because symptoms are often not noticed until vision is substantially impaired. Regular eye exams are essential so that treatment can begin as early as possible.

Macular degeneration is the leading cause of blindness among people over age 55. It is a disturbance of the center of the retina, called the macula. The macula is the source of our most accurate and detailed vision. When the macula is damaged, central vision is lost. Peripheral vision may remain but the ability to read, or to see faces, is impaired. About 70 percent of patients have the “dry” form, a thinning of tissues and disturbance in pigmentation. Others have the “wet” form, which accounts for the most severe loss of vision. To a person with macular degeneration, straight lines will appear distorted and color perception may change. A dark, blurry area, or “white out” appears in the center of vision.

There is no known cure, though there may be periods of slower progression. Treatment seeks to arrest or to slow the progression of the disease. Laser surgery to blood vessels may help to stabilize, but will not improve, the vision. Many doctors believe that a diet with high levels of antioxidants is protective and will slow the course of the disease. A recent Brigham and Women’s Hospital study came to the same conclusion. This means plenty of dark green vegetables and vitamins A, E, C and possibly zinc and selenium. Didn’t our mothers tell us to eat our spinach and carrots? Other factors that may accelerate the course of macular degeneration are hypertension and a history of smoking.

Non-age related macular degeneration might be linked to heredity, head trauma or other factors. Surgery to remove scar tissue may be effective for younger patients but is not promising for older adults.

Cataracts are most common among older people, though cataracts in mid-life do occur. About half the over-65 population have some cataract development. A cataract is a clouding of the crystalline lens, a clear tissue located behind the pupil of the eye. The progression, to the point of needing surgery, can be from several months to several years. Surgery to remove the diseased lens is the only treatment. The lens is replaced by an implant made of plastic, usually inserted at the time that the lens is removed. The lens implant cannot adjust to various distances, as does one’s natural lens, so the implant is usually calculated to a mid-range distance. Multi-focal lenses are now being evaluated.

Other eye problems can be frightening but are usually not signs of impending loss of vision. Floaters — those little specks of matter that sometimes interfere with vision — are common and usually not serious. They should be checked, however, to make sure that the retina is not torn or detached. Dry eyes, in which the tear glands don’t make enough tears, can be treated with drops. Excessive tearing may indicate an infection, or a blocked duct. Conjunctivitis causes the tissue that lines the eyelid and covers the sclera (the “white of the eye”) to become inflamed. This can be treated with medication.

The impact of UV-B light on one’s eyes is another environmental concern. “We know that UV-B light causes protein damage,” says Dr. Jaeger, “and the lens of the eye is largely protein.” Indeed, many people now routinely wear sunglasses for outdoor activity. But they may not realize that a great deal of light comes from below — from the water, the snow or the pavement that reflects the rays back up to the eyes. He advises using sunglasses that fit the contour of the face.

Research is ongoing to better understand causes and to find cures. New approaches for treatment of glaucoma are now in clinical trials. There are also new techniques that may be successful for a small percent of persons with new onset, wet macular degeneration.

In the long run, genetic research offers great promise. Scientists have identified a gene that is strongly associated with risk for age-related macular degeneration. From identification to application of this knowledge, however, will take years. Someday, glaucoma patients may benefit from current research into ways to restore damaged nerves in persons with spinal cord injuries, but that, too, is years in the future.

For the present, the single most critical factor in preventing loss of vision is early detection of eye disease. General guidelines are that adults between ages 40 and 60 should have a comprehensive evaluation every two years. After age 60, an annual exam is recommended. Persons with eye disease, diabetes and hypertension will need more frequent exams. NH