What Sunglasses Do for You
By Bruce P. Rosenthal, OD
If you have a vision impairment, controlling indoor and outdoor light can make a big difference in how you handle many of your day-to-day activities. Light is essential for vision. Yet, too much light can make seeing more difficult. Sunglasses, also known as absorptive lenses, can help you manage glare and enhance contrast. Here's some information to better understand what these lenses are and what they can do for you.
A Brief History
The concept of using lenses to control light is not new. Throughout history, people have tried various ways to minimize the effects of bright light and glare. The Eskimos used whalebone goggles with slits to reduce glare off the ice when they went hunting. The Chinese invented the Tcha Chi, a tea lens with brown tint. Green lenses were developed in England in 1561 to aid ailing eyes. But it wasn't until 1870 that a special lens was produced to absorb ultraviolet (UV) light.
Ultraviolet Light
Ultraviolet (UV) light is invisible but harmful. Most people are aware of its danger to their skin, but may not realize that it can also affect vision. UV light is generally divided into three types: UV-A, UV-B and UV-C. UV-A and UV-B are thought to contribute to various eye disorders and skin cancer. UV-C is blocked by the earth's atmosphere and generally is not a concern.
Prolonged exposure to UV light can lead to cataracts, conjunctival pterygium (fleshy growth on the surface of the eye) and corneal problems (keratopathy). In addition, recent research cites excessive sun exposure as a risk factor for age-related macular degeneration. Ultraviolet protection is especially important for people after cataract surgery. Although the lens implant following the surgery contains some UV blocking agents, it does not provide the same degree of protection to the macula as does the natural lens.
How Sunglasses Work
Sunglasses keep certain wavelengths of light from entering the eye. They can reduce the amount of light entering the eye, protect against harmful UV light, decrease glare and increase contrast. They come in tints ranging from very light to very dark. And by absorbing or transmitting specific wavelengths of light, sunglasses -- also called absorptive lenses -- can be helpful for people with conditions such as Cataracts , Glaucoma, Diabetic Retinopathy, Retinitis Pigmentosa, albinism and Macular Degeneration.
Look for a label indicating that the lenses absorb
99 -100 percent of UV light, particularly UV-B. An ultraviolet-blocking coating can also be put on any lens, regardless of the degree of tint. However, a coating does not block as much UV light as the protective lens will. Don't assume that because a lens is dark that it is UV protected. Read the label.
Understanding the Options
Absorptive lenses come in many tints, with varying degrees of light transmission. There are no set rules to determine which type of absorptive lens is recommended, but we find that people with certain eye conditions may prefer specific colors. Individuals with glaucoma or ischemic optic neuropathy may perceive the world as being "too dark." As a result, they may show a preference for yellow lenses, which increase the apparent brightness of objects or surroundings, and may enhance contrast both indoors and outdoors. Yellow lenses, for example, may help a person see a golf ball. People with macular degeneration may favor an orange, yellow-orange or plum tint outdoors; people with retinitis pigmentosa (a night-blinding condition) may prefer an orange or red tint to reduce glare.
Discuss your eye condition with your eye care professional or low vision specialist (optometrist or ophthalmologist) to learn which absorptive lenses best suit your needs. When prescribing absorptive lenses, your doctor will consider your particular visual condition along with the following factors: which wavelengths of light to block out, how sensitive you are to glare and whether you need to increase contrast. Depending on your lifestyle, you may require more than one type of tint, and you may find it helpful to wear them indoors as well as outdoors.
Dealing With Changes in Light Levels
Many people with normal vision have a difficult time adapting to abrupt changes in light levels. A prime example is when one enters a movie theater. These changes can be even more problematic for someone with a vision impairment. Without the use of absorptive lenses, it may take anywhere from five to 30 minutes to adjust to lighting changes. Wearing absorptive lenses outdoors may decrease the adjustment time indoors.
Sunglasses: Designs and Lenses
Sunglasses are available in various designs that can fit over your glasses, slip behind regular glasses, clip on or flip up. They are also available with top and side shields (wrap-around frame) that cut out light from those sources. Anti-reflective coating, added to the UV coating, may also reduce glare.
There are glass as well as plastic photochromic lenses that get darker in sunlight as well as fluorescent light. They are available in all types of prescriptive and plano (no prescription) lenses including single vision, bifocals, and trifocals.
One of the easist ways to protect your vision is to wear sunglasses when you are outdoors. This applies to everyone from infancy to old age. Hats and visors are also recommended, particularly when you are outdoors for long periods of time. Sports enthusiasts, including snow skiers, will find that tinted lenses will not only protect against UV light but also increase visibility by enhancing contrast.
Bruce Rosenthal, OD, is Chief of Low Vision Programs at Lighthouse International