The Sun Is Damaging Your eyes
October 14, 2008
The sun is a blessing to all life on this planet earth. It warms the earth to the right temperature and provides the energies needed to run the various ecosystems. The sun provides adequate light to enable clear vision during the day.
Human beings are able to see only if light travels from an object to the eye. The light passes through the cornea, lens of the eye and some fluid media in the eye before reaching the retina. The retina is the most important part of the eye because it is the only tissue of the eye that is capable of converting the light energy entering the eye into electrical impulses that the brain can understand. Without the retina we cannot see.
The energy from the sun is in the form of electromagnetic waves and it comprises a wide spectrum of which visible light is just a minute fraction. The visible light spectrum is made up of red, orange, yellow, green, blue, indigo and violet lights. Beyond red and violet waves are other waves with the eye cannot detect. These include infrared, terahertz, microwave, radio waves, ultraviolet, x-ray and gamma waves.
Ultraviolet (UV) radiation comprises invisible high energy rays from the sun that lie just beyond the violet end of the visible spectrum. The UV radiation present in sunlight is not useful for vision. Excessive exposure to UV radiation causes serious damage to the eye and is also associated with age related changes in the eye and the skin.
Ultraviolet radiation in sunlight is commonly divided into two components: UV-A which causes tanning and contributes to ageing of the skin and skin cancer, and UV-B which causes sunburn and skin cancer especially in Caucasians.
UV-B is more damaging because it has higher energy. Most of the UV-B is absorbed by the cornea and lens of the eye; therefore it can cause damage to these tissues but will not normally damage the retina. However, the retina can be damaged if exposed to UV-B. UV-A radiation has lower energy, but penetrates much deeper into the eye and may also cause injury.
Ultraviolet radiation plays a contributory role in the development of various ocular disorders including photokeratitis, pterygium, cataract, cancer of the skin around the eye and may contribute to age-related macular degeneration.
Photokeratitis is a reversible sunburn of the cornea resulting from excessive UV-B exposure. It occurs when one spends long hours on sunlight without eye protection. It can be extremely painful for 1 to 2 days and can result in temporary loss of vision.
Pterygium is a growth of tissue on the white of the eye that may extend onto the clear cornea where it can block vision. It is seen most commonly in people who work outdoors in the sun and wind, and its prevalence is related to the amount of UV exposure. A pterygium can be removed surgically, but often recurs and can cause cosmetic concerns and visual loss if untreated.
Cataract is a major cause of visual impairment and blindness world-wide. Cataracts are a cloudiness of the lens inside the eye that occurs over a period of many years. Excessive exposure to UV radiation, especially UV-B causes cataract.
Age-related macular degeneration is the major cause of reduced vision in people over the age of 55. The macula is a small yellowish spot in the middle of the retina that provides the greatest visual acuity and colour perception. When we look at an object critically it is the macula that is at work. Exposure to UV and intense violet/blue visible radiation is damaging to retinal tissue.
No one is immune to sunlight-related eye disorders. Any factor that increases sunlight exposure of the eyes will increase the risk for ocular damage from UV radiation. Individuals whose work or recreation involves lengthy exposure to sunlight are at greatest risk. The risk is greatest during the mid-day hours, from 10 am to 3 pm, UV levels are also greater at high altitudes.
Since the human lens absorbs UV radiation, individuals who have had cataract surgery are at increased risk of retinal injury from sunlight unless a UV absorbing intraocular lens was inserted at the time of surgery.
Children are not immune to the risk of ocular damage from UV radiation. Children typically spend more time outdoors in the sunlight than adults. Solar radiation damage to the eye may be cumulative and may increase the risk of developing an ocular disorder later in life.
Ultraviolet radiation reaches the eyes not only from the sky above but also by reflection from the ground, especially water, snow, sand and other bright surfaces. Protection can be achieved by simple, safe and inexpensive methods such as wearing a brimmed hat and using spectacles that absorbs UV radiation.
A wide-brimmed hat or cap will block roughly 50 per cent of UV radiation and reduces UV that may enter above or around the glasses. Ultraviolet-absorbing spectacles provide the greatest measure of UV protection, particularly if it has a wrap-around design to limit the entry of peripheral rays.
It is prudent to protect the eyes of children against UV radiation by wearing a brimmed hat or cap and sunglasses. Sunglasses for children should have lenses made of plastic rather than glass for added impact protection.
Ideally, all types of eyewear including prescription spectacles, contact lenses and intraocular lens implants should absorb the entire UV spectrum (UV-A and UV-B). Polarisation or photosensitive darkening are additional sunglass features that are useful for certain visual situations, but do not, by themselves, provide UV protection.
For outdoor use in the bright sun, sunglasses that absorb 99-100 per cent of the full UV spectrum are recommended. Individuals who wear clear prescription eyewear outdoors should consider using lenses which absorb 99-100 per cent of the UV radiation.