Sunglasses have been used since many years ago, either for fashion or to provide greater comfort against the intense sunlight. Ophthalmologists believe that there is another reason to use sunglasses, which is maintaining long-term health of your eyes in different conditions.
Several studies during the last ten years have shown that long hours in the sun without adequate eye protection, increases the risk of eye disease.
In 1988, a group of ophthalmologists conducted a study on 838Chesapeake Bay fishermen who had spent many years of their lives on water. The fishermen who had no eye protection suffered from cataract 3 times more, compared with those who wore sunglasses or caps. Cataract is, in fact, the opacity of natural lens of the eye.
Based on this study and other studies, currently ophthalmologists recommend that whenever you are against the sun, to the extent that there is a possibility of sun tan or risk of sunburns, wear ultraviolet absorbent sunglasses, especially if you live on the heights or near the equator.
Different Types of Sunglasses
Sunglasses Manufacturers have created new designs in order to protect the eyes against the harmful effects of the sun. They promise to protect our eyes against ultraviolet rays or other natural types of radiation, but it should be noted that the protection against some of these rays is crucially important.
Blocks 99% of ultraviolet rays
It is recommended that you should always buy sunglasses with this feature. Long-term exposure to ultraviolet (UV) radiation in sunlight is related to some eye disease.
Both plastic and glass lenses absorb some UV light, but UV absorption can be improved by adding chemicals to the basic lens material or coating the lens with special materials.
You should always buy sunglasses that block 99% or 100% of all UV light. Some manufacturers attach labels saying “UV absorption up to 400nm.” This is the same thing as 100% UV absorption.
Blocks 90% of infrared rays
Infrared wavelengths are invisible and produce heat. Sunlight has low levels of infrared rays, and the eye tolerates infrared well.
Some sunglass manufacturers claim that their products can protect the eyes against infrared rays, but research has not shown a close connection between eye diseases and infrared rays.
Whether blue light is harmful to the eye is still controversial. Lenses that block all blue light are usually amber tinted and make your surroundings look yellow or orange. This tint causes distant objects appear more distinct, especially in snow or haze. That is why amber sunglasses are usually worn by skiers, hunters, boaters, and pilots
Polarized lenses diminish sun glare—sunlight that reflects off smooth surfaces like pavement or water. They can be particularly useful for driving and fishing.
Polarization has no effect on UV light absorption, but many modern polarized lenses can block UV radiation. Check the label to make sure whether the lenses provide maximum UV protection or not.
Mirror finishes are in fact thin layers of various metallic coatings on ordinary lenses. Although they do reduce the amount of visible light entering your eyes, they won’t fully protect your eyes against UV radiation.
Wraparound glasses are designed to keep light from shining around the frames and into your eyes.
Studies have shown that the amount of UV rays entering around ordinary eyeglass frames is so much that it can reduce the benefits of protective lenses. Wraparound sunglasses which have large frames are useful, since they protect your eyes from all angles
Gradient lenses are shaded from top to bottom or from top and bottom toward the middle, and in fact are gradients. Single-gradient lenses (dark on top and lighter on the bottom) can cut glare from the sky while they allow you to see clearly below. They are useful for diving because they don’t dim your view of the diving board. They’re not as good, however, at reducing glare in snowy surroundings or at the beach, especially if they are lighter 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.
A photochromic glass lens automatically darkens in bright light and becomes lighter in low light. Most of the time, the darkening takes place in about half a minute, while the it takes about five minutes to lighten. Photochromic lenses come in a uniform or gradient tint. Although photochromic lenses may be good in absorbing UV radiation, it takes time for them to adjust to different light conditions
Ground and polished
Some nonprescription glasses are ground and polished by their manufacturers to improve the quality of the lenses as much as possible. Of course nonprescription lenses that are not ground and polished will not hurt your eyes.
First of all make sure that the lenses you buy are made properly. To judge the quality of nonprescription sunglasses, look at something with a rectangular pattern, such as the floor tiles of your room. 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, you’ve chosen the correct lenses. But if the lines wiggle, especially in the center of the lens, try another pair.
All sunglasses must meet impact standards set by the Federal Food and Drug Administration (FDA) for safety. (So far, in our country, there has been no control over producing or selling them and wearing them is mostly ornamental rather than protective.) No lens is really unbreakable, but plastic lenses are less likely than glass lenses to shatter when hit by a ball or stone.
Most nonprescription sunglass lenses are made of plastic. Although Polycarbonate plastic, used in many sports sunglasses, is tough, it scratches easily. If you are going to buy polycarbonate lenses, choose ones with scratch-resistant coatings.
A medium lens is good for day-to-day wear, but if you are going to use your glasses in very bright conditions, you should choose a darker lens.
The color and the degree of darkness are irrelevant to the lenses’ ability to block UV light, so you can’t be sure about their ability to absorb harmful radiations, based on their color.
People with Increased Risk of Eye Damage from UV Light
Some people are more prone to eye diseases caused by UV radiation. People with certain eye diseases (such as macular degeneration and retinal dystrophy) should protect their eyes in outdoor conditions.
Cataract surgery patients
In our country, thousands of people have cataract surgery each year. During this procedure, the eye’s natural lens is removed, thus the eye is more vulnerable to UV light.
During cataract surgery, the natural lens is usually replaced by an intraocular lens (IOL). Older intraocular lenses absorb less UV light than ordinary glass or plastic eyeglass lenses. Now, manufacturers of IOLs make most of their products UV-absorbent.
If you have had cataract surgery and your IOL is not the newer UV-absorbent type, it is recommended to wear UV-blocking sunglasses and for added protection wear a hat. If, during cataract surgery, your lenses are not replaced by LOL, there is risk of UV damage to your eyes.
Contact lens wearers
Contact lenses do not protect your eyes from UV light by themselves. However, there are contact lenses available with UV protection. If your contact lenses don’t absorb UV light, you need to protect your eyes with sunglasses.
Photosensitizing drug users
Photosensitizing drugs (drugs that make your skin more sensitive to light) can make your eyes more sensitive to light as well.
You should consult with your ophthalmologist if you are taking any of the following drugs:
- Psoralens (used in psoriasis treatment)
While you take these drugs, wear UV-absorbent sunglasses and a cap whenever you go outside.
Even the best sunglasses cannot protect your eyes from intense light sources. Arc welding, tanning lights, snowfields, or gazing directly at the sun (e.g. during Eclipse) can severely damage your eyes. Looking straight at any of these light sources without enough protection can cause a painful corneal condition called photo keratitis or even a permanent loss of central vision.
For general outdoor activities, proper sunglasses are key to protecting your eyes from sun-related damage. The best sunglasses are those which 100% absorb UV, have the best optical quality, and are impact resistant.