Sunglasses are a popular fashion accessory, but their most important function is to protect the eyes from the harmful ultraviolet rays of the sun. Ultraviolet (UV) radiation from the sun can damage not only the skin of the eyelid but also the delicate parts of the eye itself. Long term exposure contributes to the development of eye conditions including cataracts and macular degeneration.
Ultraviolet (UV) light is electromagnetic radiation that is invisible to the human eye. The sun emits three types of ultraviolet radiation. UVA makes up the vast majority of the ultraviolet radiation reaching the Earth's surface. It is capable of penetrating deep into the skin and is thought to be responsible for up to 80% of skin ageing. UVB can damage the DNA in the skin leading to sunburn. UVC rays are filtered out by the Earth's ozone layer and rarely reach the earth.
UV light is absorbed by molecules which are present in the eye cells and tissues. If too much UV light is absorbed, over time eye structures, such as the cornea, the lens and the retina can be damaged. The longer the eyes are exposed to solar radiation, the greater the risk of developing conditions such as cataracts or macular degeneration later in life.
There are various light sources that have an effect on the eyes. Direct light is light that goes straight from the light source (like the sun) to the eyes. Reflected light is light that has bounced off a reflective object such as water, sand or snow to enter the eyes. It is usually in the form of glare. Ambient light is light that has bounced and scattered in many directions so that it is does not seem to have a specific source, for example the glow in the sky around a major city. Ambient light makes it possible for us to see when there is no direct source of light.
Sunglasses make it easier and more comfortable to see on a bright, sunny day, but the lenses should do more than just shade the eyes. The best sunglasses are equipped with technology that wards off the damaging effects of UV rays. A good pair of sunglasses has four important functions. It should provide protection from ultraviolet rays in sunlight. It should provide protection from intense light. It should provide protection from glare. It should eliminate specific frequencies of light and enhance contrast, making them work better in specific situations.
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With the thousands of sunglasses available and the importance of protecting the eyes, choosing the right sunglasses can be overwhelming and confusing. Lenses that offer UV protection are built with a special coating that absorbs, blocks, and reflects UVA and UVB rays, preventing them from penetrating through the lens and into the eye. Before purchasing a pair of sunglasses, make sure they offer 100% UV protection and that the technology is built into the lens rather than simply a top coating that can wear off over time. |
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There are a number of guiding principles to be aware of.
- The label on some sunglasses may state "block UV" without saying how much UV light is blocked. They need to block 99 to 100% of UV rays.
- The absorption of UV light can be improved by adding a special UV coating to the lenses of the plastic and glass sunglasses. Polycarbonate lenses offer 99% UV protection.
- Do not assume that mirror coating will protect your eyes. Check the label!
- Antireflective coating reduces the reflections that bounce off the back of the lenses into the eyes.
Sunglass lenses with a gradient tint 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) are useful for driving because they reduce glare while allowing you to see clearly. Double gradient lenses are better for sports.
Polarised lenses are the best way to reduce or eliminate reflected glare, such as sunlight that bounces off smooth surfaces like snow or water. Polarisation does not have any relation to UV light absorption, but many lenses are now combined with a UV coating. Be sure to check the label.
Photochromic lenses change from light to dark depending on the level of light. Although some photochromic lenses may be good UV-absorbent sunglasses, it takes time for them to adjust to different light conditions.
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The tint colour and darkness of the lenses are no indication of the ability of the sunglasses to block UV rays. It is purely personal choice, but certain qualities are worth considering. Grey lenses reduce the overall amount of brightness with no contrast or colour distortion and offer good protection against glare. A yellow tint virtually eliminates the blue part of the colour spectrum and makes everything bright and sharp, but it distorts colour perception. Amber and brown are good general-purpose tints and have the added benefit of reducing glare. They may help prevent cataracts over time. They can distort some colours but increase contrast and clarity. Green is a popular tint for multi-use, reduces glare and offers the highest colour contrast with little colour distortion. Rose and pink tints are best for computer eye strain but cause some colour distortion. The degree of darkness does not represent the lenses' ability to block UV light, so be sure to check the label. |
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Other features to consider include the lens material, quality and design and the frame choice. Polycarbonate lenses are light weight and resistant to impact, whereas glass lenses are heavier but more resistant to scratches. Optical-quality polycarbonate and glass lenses are free of distortions, such as blemishes or waves, and have evenly distributed colour across each lens. The frame design is important in terms of protecting the eyes from ambient light, direct light and glare. Wrap around frames and larger lenses offer the best protection but are not to everybody's taste. Certain brands are associated with quality, but a brand name does increase the cost of the sunglasses and it is possible to find high quality sunglasses that do not have a brand name. |
Your optometrist can guide you and help you select the best sunglasses for your specific needs.