The sun’s rays are made up of several parts, not only the visible part we perceive and that allows us to see, but also rays that are invisible to the eye. The invisible rays is mainly made up of infra-red radiation, which does not cause eye damage, and ultraviolet radiation (UV), which can cause damage to the eye.
There are three types of UV radiation: UVA, UVB and UVC. UVC radiation is the most harmful, but it is completely blocked by the earth’s atmosphere and, in normal conditions, does not reach the surface of the Earth. UVB radiation reaches the earth’s surface but is almost completely absorbed by the cornea (the outermost part of the eye), whereas UVA radiation, meanwhile, is blocked mainly by the crystalline lens (the eye’s transparent intraocular lens that helps us focus on images).
Prolonged exposure to sunlight, without proper protection, can cause eye damage from UV radiation. In the outermost parts of the eye, such as the eyelids, UV radiation is an important factor in certain types of cancer (squamous cell carcinoma). In terms of the cornea, it can cause acute photokeratitis (similar to a “superficial burn”), which can require emergency treatment due to the great pain and damage to vision it causes, although there are no subsequent consequences after recovery.
In terms of the connective tissue, UV radiation can lead to the appearance of pterygium (a reddish deposit in a triangular shape in the white of the eye that can invade the cornea) or pinguecula (a nodular yellow deposit that does not invade the cornea). These are both benign lesions that are a form of defence against the aggressive nature of solar radiation. In terms of the internal eye, UV radiation can contribute to cataracts forming (progressive opacification of the lens), and can cause acute retinal damage (radiation retinopathy from looking directly at the sun, for example during a solar eclipse, without adequate protection). It can also be a contributing factor to chronic damage that can progress to significant visual impairment, such as age-related macular degeneration (AMD).
To prevent UV radiation damage, it is advisable to avoid exposure to the sun when it is at its highest intensity (from 10 am to 2 pm). Use hats with a wide brim and wear sunglasses that completely block out UV radiation. In order to acquire glasses that offer suitable protection, you should check that they meet the following requirements, as recommended by European regulations: CE marking, “100% UV” protection (total protection against UV radiation) and the correct category in terms of protection against visible solar rays (category 0: filters up to 20% of the rays, category 1: between 20%-57%, category 2: between 57%-80%, category 3: between 80%-90% and category 4: over 90%). Categories 2 and 3 provide sufficient protection for daily activities and driving, while category 4 is required for activities with high exposure to sunlight, such as in desert areas or mountains.
It is important to remember that eye protection should start from childhood, since this age involves more outdoor activities and, additionally, certain defence mechanisms have not yet fully developed, such as the crystalline lens filtering UV radiation, for example.