What is invisible light?
Harmful ultraviolet (UV) rays from the sun do not fall within the realm of visible light and form a portion of the spectrum of invisible light from 286nm (nanometers) to 400nm. This portion of invisible light is deemed to be harmful to the eyes.
The harmful effects of invisible UV light:
UV light is divided into three segments (A, B and C) according to wavelength:
• UV-A rays (320 – 400nm) have lower energy than UVB or UVC rays, but are the most damaging portion of UV radiation, as they can be transmitted through the cornea to reach and cause damage to the lens and retina inside the eye. Overexposure has been linked to the development of cataracts and may play a role in the development of age-related macular degeneration (AMD).
• UV-B rays (286 – 320nm) are partially filtered by the ozone layer, but some still reach the surface of the earth. At low levels of exposure, UVB radiation stimulates the production of a skin pigment called melanin, which cause the skin to darken, creating a typical suntan. Melanin acts as the body’s natural sunscreen and is also found inside the eye. At higher levels of exposure the UVB rays are harmful to the eyes, as it is absorbed by the cornea. This can lead to growths on the surface of the cornea. Short term – but high exposure – doses can lead to inflammation of the cornea, typified by “snow-blindness.” UVB rays are also the cause of sunburn and other skin damage that can eventually lead to discolorations, wrinkles and an increased risk of skin cancer.
• UV-C rays (below 286nm) are the highest-energy rays, but are fortunately effectively filtered by the ozone layer surrounding the earth. Depletion of the earth’s ozone layer could potentially cause serious UV-related health problems.
Protecting the eyes from the harmful effects of invisible UV light:
• It is important to protect the eyes from the sun’s harmful UV rays, as exposure to the ultraviolet radiation in sunlight can over time lead to damage of the eye and some eye disorders. Looking directly into the sun, even during a solar eclipse, can cause permanent damage to the retina.
• When choosing sunglasses, be aware that not all sunglasses are created equal – the degree of UV protection is crucial to prevent damage to the eyes. Choose a pair that blocks 100% of the harmful UV-A and UV-B rays. Avoid sunglasses whose labels indicate they are UV absorbent! Sunglasses should be labelled UV 400.
• Children also need to protect their eyes from accumulated damage over time, by wearing proper sunglasses. In addition, the lens inside a child’s eye is clearer than an adult’s and can enable more UV to penetrate deep into the eye.
• The colour and darkness of the lenses of sunglasses play no role in the amount of UV protection, as long as the lenses offer 100% UV protection.
• Being in the shade offers some protection from UV rays, but they are still reflected from buildings, water, roads and other surfaces, so it is a good precaution to also wear sunglasses in the shade.
• Polarized lenses cut out the glare but not the UV rays. Select sunglasses with polarized lenses that also offer 100% UV protection.
• The cost of a pair of sunglasses is not an indication of the effectiveness against harmful UV rays, but whether it offers 100% protection against both UB-A and UV-B rays.
• Bigger sunglasses also offers more coverage for better protection to the eyes and also to the sensitive skin around the eyes.
• Wearing a hat on sunny days will reduce the eyes’ exposure to UV rays.
• Lenses for sunglasses can be specified to include synthetic melanin, which filters the colours in proportion to their damage potential, further reducing the risk of macular degeneration. Such lenses also offer protection from high energy visible (HEV) light, such as violet and blue light.
• Some contact lenses offer UV protection, but it is advisable to still wear sunglasses for an extra layer of protection.
Sources:
Ultraviolet (UV) radiation and your eyes. Information updated April 2018. All About Vision. (www.allaboutvision.com)
How to choose the best sunglasses. Published 1 May 2015. American Academy of Ophthalmology. (www.aao.org)
Keeping your eyes healthy: Wear sunglasses. Published by the National Eye Institute, part of the National Institutes of Health (USA). (www.nei.nih.gov)
Ultra-violet and blue light aggravate macular degeneration. Published by the American Macular Degeneration Foundation. (www.amdf.org)
Our lenses & the difference. Published by ESP Eyewear. (www.espeyewear.com)
HEALTH INSIGHT
MAY 2018
