Optometrists have long known the impact of ultraviolet (UV) light radiation that can result in cataract development, age related macular degeneration and even pterygia or pingueculae.
But these conditions continue to increase in prevalence even though many contact lenses, IOLs and spectacles have UV protection coatings. This paper looks at the latest understanding of UV exposure and some of the more common as well as rare diseases that optometrists face when it comes to UV damage.
UV Exposure and Ocular Health
There are three forms of ultraviolet light--UVA, UVB and UVC.
UVA has a wavelength of 315nm to 380nm and penetrates deeply into the skin. This is often associated with tanning, but also is linked to skin aging.
UVB has a wavelength that is even smaller, between 280nm to 315nm. UVB does not penetrate into the skin as deeply as UVA because the epidermis mostly absorbs it. Thus, it can be a more damaging form of ultraviolet light that can cause erythema or sunburn, blistering of the skin, and potentially various skin cancers.
UVC ranges from 100nm to 280nm in wavelength and is the most harmful to the skin, also resulting in skin cancer. Fortunately, most of it is absorbed by the ozone layer and does not reach the Earth's surface.
The sunlight that does reach the r Earth is comprised of approximately 95% UVA light and 5% UVB/UVC.
UVB and especially UVC are directly absorbed by DNA molecules, so this is why experts believe that these have the greatest impact on altering skin tissue and are associated with skin cancers. (1)
UVC is also the form that plays a key role in cataract genesis, as well as macular degeneration. (2) UVC can actually form free radicals that directly affect the DNA. This has the ability to disrupt structures such as collagen, which are prevalent in the cornea and conjunctiva, as well as glycans such as hyaluronic acid.
On the other hand, some sun exposure is critically important to vitality, as it delivers vitamin D. In fact, many experts believe a vitamin D deficiency exists in the United States, which results in significant morbidity. (3)
Fortunately only 1% of all UV light from the atmosphere reaches the retina. (4) Most is absorbed at the cornea and the lens, which essentially work as filters to prevent its penetration.
Furthermore, transmission of UV light through the lens decreases greatly with age. (5) For example, a 10-year-old has a 75% or greater lens transmission rate. By age 25, the transmission drops to 10%. It is remarkable that this change happens within such a short span of years, and the amount of UV light transmission only decreases as age increases. Specifically, 80% of all the damage patients experience may well happen before age 18.
Ocular Diseases Associated with UV Exposure
* Photokeratitis: Photokeratitis--more commonly known as "snow blindness"--is essentially an inflammation of the cornea secondary to UV exposure. The condition is much more likely to be found by practitioners who live in ski resort areas...
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