Eye Health & Education.

Manufacturers have developed new sunglasses designed to protect eyes from the sun’s harmful effects. They promise protection from ultraviolet light and other kinds of natural radiation. It is more important to protect your eyes from some kinds of light than others.

• “Blocks 99% of ultraviolet rays”: You should always buy sunglasses with this feature. Long-term exposure to ultraviolet (UV) radiation in sunlight is linked to eye disease. Both plastic and glass lenses absorb some UV light, but UV absorption can be improved by adding chemicals to the lens material during manufacturing or by applying special lens coatings. Shop for sunglasses that block 99 or 100% of all UV light. Some manufacturers’ labels say “UV absorption up to 400nm.” This is the same thing as 100% UV absorption.

• “Blocks 90% of infrared rays”: Infrared wavelengths are invisible (they are longer than light rays that you can see) and produce heat. Sunlight has low levels of infrared rays, and the eye tolerates infrared well. Some sunglasses manufacturers make health claims for their products based on infrared protection, but research has not shown a close connection between eye disease and infrared rays.

• “Blue-blocking”: Whether blue light is harmful to the eye is still controversial. Lenses that block all blue light are usually amber and make your surroundings look yellow or orange. The tint supposedly makes distant objects appear more distinct, especially in snow or haze. For this reason, amber sunglasses are popular among skiers, hunters, boaters and pilots.

• “Polarized”: Polarized lenses cut reflected glare – sunlight that bounces off smooth surfaces like pavement or water. They can be particularly useful for driving and fishing. Polarization has nothing to do with UV light absorption, but many polarized lenses are now combined with a UV-blocking substance. Check the label to make sure the lenses provide maximum UV protection.

• “Mirror-coated”: Mirror finishes are thin layers of various metallic coatings on an ordinary lens. Although they do reduce the amount of visible light entering your eyes, do not assume they will fully protect you against UV radiation.

• “Wraparound”: Wraparound glasses are shaped to keep light from shining around the frames and into your eyes. Studies have shown that enough UV rays enter around ordinary eyeglass frames to reduce the benefits of protective lenses. Large-framed wraparound sunglasses can protect your eyes from all angles.

• “Gradient”: Gradient lenses are permanently shaded from top to bottom or from top and bottom toward the middle. Single-gradient lenses (dark on top and lighter on the bottom) can cut glare from the sky but allow you to see clearly below. They are useful for driving because they don’t dim your view of the dashboard. But they’re not as good on snow or at the beach, especially if they’re clear on the bottom. Double-gradient lenses (dark on top and bottom and lighter in the middle) may be better for sports where light reflects up off the water or snow, such as sailing or skiing. Double-gradient lenses are not recommended for driving, because they make the dashboard appear dim.

• “Photochromic”: A photochromic glass lens automatically darkens in bright light and becomes lighter in low light. Most of the darkening takes place in about half a minute, while the lightening takes about five minutes. They come in a uniform or gradient tint. Although photochromic lenses may be good UV-absorbent sunglasses (again, the label must say that), it takes time for them to adjust to different light conditions.

• “Ground and polished”: Some non-prescription glasses are ground and polished when they are manufactured to improve the quality of the lenses. Non-prescription lenses that are not ground and polished will not hurt your eyes. You do want to make sure that the lenses you buy are made properly. To judge the quality of non-prescription sunglasses, look at something with a rectangular pattern such as floor tile. Hold the glasses at a comfortable distance and cover one eye. Move the glasses slowly from side to side, then up and down. If the lines stay straight, the lenses are fine. If the lines wiggle, especially in the center of the lens, try another pair.

• “Impact resistant”: All sunglasses must meet impact standards set by the Federal Food and Drug Administration. No lens is truly unbreakable, but plastic lenses are less likely than glass lenses to shatter when hit by a ball or stone. Most non-prescription sunglass lenses are plastic. Polycarbonate plastic, used in many sports sunglasses, is especially tough but scratches easily. If you buy polycarbonate lenses, look for ones with scratch-resistant coatings.

A medium lens is good for day-to-day wear, but if you use the glasses for very bright conditions, choose a darker lens. The color and the degree of darkness do not tell you anything about the lenses’ ability to block UV light.

There are some people who are at greater risk for UV-related eye damage. People with certain eye diseases, such as macular degeneration or retinal dystrophies, need to protect their eyes whenever they go outside, no matter how briefly.

Cataract surgery patients

One million Americans have cataract surgery each year. During this procedure, the eye’s natural lens is removed, leaving the eye more vulnerable to UV light. During or after cataract surgery, the natural lens is usually replaced by an intraocular lens (IOL). Older intraocular lenses absorb much less UV light than ordinary glass or plastic eyeglass lenses. Manufacturers of IOLs now make many of their products UV absorbent. If you have had cataract surgery and your IOL is not the newer UV-absorbent type, you may want to wear sunglasses and a hat for added protection.

Contact lens wearers

Contact lenses by themselves will not protect your eyes from UV light. Many types of contact lenses are available with UV protection. If you do not have contact lenses that absorb UV light, you still need to protect your eyes with sunglasses.

Photosensitizing drugs

Photosensitizing drugs–drugs that make your skin more sensitive to light –can make your eyes more sensitive to light as well. You should discuss precautions with your ophthalmologist if you are taking any of the following drugs:

• Psoralens (used in treating psoriasis)

• Tetracycline

• Doxycycline

• Allopurinol

• Phenothiazine

Wear UV-absorbent sunglasses and a hat whenever you go outside for as long as you take the drug.

Ordinary sunglasses, even the best, cannot protect your eyes from certain intense light sources. Arc welding, tanning lights, snowfields or gazing directly at the sun (especially during a solar eclipse) can damage your eyes. Looking at any of these light sources without adequate protection can cause a painful corneal condition called photokeratitis or even a permanent loss of central vision.

There are many benefits from an outdoor lifestyle. However, it is important to recognize that sunlight is a substantial source of UV radiation which may damage tissues of the eye. At risk from sunlight, or strong artificial UV sources, are the ocular surface (snowblindness and pterygium), the lens (cataract), and the retina (eclipse blindness and macular degeneration).

Ultraviolet radiation is divided into two major bands, UV-A and UV-B. UV-A is longer wavelength radiation, close to blue in the visible spectrum, that usually induces skin tanning and browning, and has been implicated in skin aging. UV-B is more active, shorter wavelength radiation that causes blistering sunburn and is associated with skin cancer.

Excessive exposure to intense sunlight, or to an artificial source such as a welding arc or suntanning lamp, can burn the surface of the eye (cornea and conjunctiva) much like sunburn on the skin. The risk is highest in environments where much UV is reflected, such as snow. Although snowblindness (photokeratitis) may be painful, it is usually self-limited with recovery in one or two days. Chronic sun exposure also contributes to other ocular surface problems such as pterygium.

Cataract (clouding of the lens) is a major health problem in the United States and the most common surgical procedure among the elderly. Globally, cataract causes half of all serious visual impairment and affects 20 million people. Several laboratory and epidemiological studies have suggested a link between sun exposure and cataract. There is debate about how close this linkage is for one common form of cataract (nuclear sclerosis), but measures to reduce UV exposure should reduce the risk of at least two types of cataract (cortical and posterior subcapsular).

Macular degeneration (age-related damage in the central vision area) is the major cause of blindness among Americans over age 50, and is an increasingly important problem as our population ages. Both UV and deep blue light have been shown to be damaging to the retina in laboratory studies, and a number of scientists have postulated that UV and blue light may contribute to retinal aging and macular degeneration. Epidemiological studies to date have not demonstrated any clear relationship, except possibly for some severe forms of the disease that seem associated with a history of greater blue light exposure.

Protection from UV (including the longer UV-A wavelengths) and from too much blue light may thus be prudent. Just wearing a hat will reduce exposure by roughly half. Sunglasses are capable of eliminating virtually all of the UV, but it may be hard to tell from the label what a particular pair of sunglasses will do. Most pairs labelled “UV absorbing” will absorb most of the UV-B, but there is no present standard of labelling that adequately indicates UV-A or blue protection.

Given the increased risk of skin cancer and some types of cataract associated with UV exposure, the public should protect their eyes, especially when exposed to excessive sunlight. If there is sufficient UV present to cause sunburn, a hat and sunglasses are advised.

People with high UV exposure, especially those spending prolonged time in the sun or in the snow during the middle of the day, or those exposed to intense artificial sources such as welding arcs or suntanning lamps, should consider using close-fitting goggles or sunglasses with lenses that absorb all UV-B and UV-A, and possibly a substantial portion of blue light as well.

Consumers should be able to determine the UV and visible light absorptive properties of sunglasses. Manufacturers are encouraged to adopt a simple coding system for sunglasses that clearly indicates the degree of UV-B and UV-A radiation, as well as the blue and visible light absorption.