Moderate exposure to ultraviolet radiation (UVR) from the sun is a necessary part of maintaining normal health (read the next blog for more about this!). However, excessive exposure to UVR has no health benefits and actually leads to adverse consequences for not only the skin, but also the eye. Interestingly, the eye occupies less than two percent of the whole body surface area, but it represents the ONLY organ system to allow the penetration of visible light deep into the human body.
So what are the known eye health effects of UVR?
Photokeratitis and photoconjunctivitis
Acute inflammation of the cornea (photokeratitis) and the conjunctiva (photoconjunctivitis) occur within a few hours of UVR exposure. These reactions can be likened to sunburn of the very sensitive tissues of the eyeball and eyelids. Photokeratitis and photoconjunctivitis are very painful conditions, but they are temporary reactions and do not seem to result in long-term damage to the eye or vision.
A pterygium is when the conjunctiva (clear membranous tissue covering the sclera or white part of the eye) becomes dysplastic and grows towards and over the cornea. Pterygium has been linked to prolonged UV exposure and is attributed to the accumulatively damaging effects of UVR. If the pterygium grows close to the pupil, it needs to be surgically removed otherwise, the eye will be blind. Pterygiums are found in 10% of Queenslanders (nearly half a million people!).
Cataracts are the leading cause of blindness in the world. The World Health Organisation estimates that up to 20% of cataracts may be caused by over-exposure to UVR. UVR is absorbed by the lens of the eye which leads to damage of the lens which may result in cataract formation. Cataract is when the lens of the eye becomes cloudy, making vision hazier and not completely correctable with glasses or contact lenses. Surgery is performed to remove the cloudy lens and replace it with a clear artificial lens.
Cancer of the eyelid
The eyelid region is one of the most common sites for non-melanoma skin cancers such as basal cell carcinoma and squamous cell carcinoma. Cancers of the eyelid account for 5 to 10% of all skin cancers of the human body. Like skin cancer of the rest of the human body, cancers of the eyelid are caused by the accumulative effects of UVR.
Age-related macular degeneration
Age-related macular degeneration is the leading cause of blindness in the western world. The retina is highly susceptible to photochemical damage from continuous exposure of light and oxygen. The cornea and lens block a major portion of UVR (see Figure 1) from reaching the retina. Although the relationship between UV light exposure and AMD is unclear, we know that short wavelength radiation (UV and even blue light from the visible spectrum) induce significant oxidative stress to the retina which may increase risk of the development of macular degeneration.
Check out our next blog to find out the best ways to protect our eyes from UV radiation!