Wearing sunglasses every day

Wearing sunglasses when exposed to the sun should be as important as using sunscreen, regardless of the season. Ultraviolet rays are invisible to humans, so it doesn’t matter whether the day is sunny or not, so believing that they affect us only in summer is a serious mistake.

The lens of the human eye blocks most radiation in the 300-400 nm wavelength range; shorter wavelengths are blocked by the cornea, and humans also lack color receptor adaptations for ultraviolet rays. However, the retina’s photoreceptors are sensitive to near-ultraviolet rays, and people who lack a crystalline lens (a condition known as aphakia) perceive near-ultraviolet rays as whitish-blue or whitish-violet. Under some conditions, children and young adults can see ultraviolet rays up to wavelengths around 310 nm.

Near-ultraviolet radiation is visible to insects, some mammals, and birds. Small birds have a fourth color receptor for ultraviolet rays; this gives birds «true» UV vision.

The Sun emits ultraviolet radiation at all wavelengths, including extreme ultraviolet where it intersects with X-rays at 10 nm. Extremely hot stars emit proportionally more ultraviolet radiation than the Sun.

The atmosphere blocks about 77% of the Sun’s UV rays when it is highest in the sky (at its zenith), with absorption increasing at shorter UV wavelengths. At ground level, with the Sun at its zenith, sunlight is 44% visible light, 3% ultraviolet, and the remainder infrared. Of the ultraviolet radiation that reaches Earth’s surface, more than 95% is the longer UVA wavelengths, and the small remainder is UVB. Almost none of the UVC radiation reaches the Earth’s surface.[16] The fraction of UVB that remains in the UV radiation after passing through the atmosphere depends strongly on cloud cover and atmospheric conditions. On «partly cloudy» days, the patches of blue sky shown between the clouds are also sources of (scattered) UVA and UVB, which are produced by Rayleigh scattering in the same way as the visible blue light from those parts of the sky. UVB also plays an important role in plant development, as it affects most plant hormones.[17] During total overcast, the amount of cloud absorption depends largely on cloud thickness and latitude, with no clear measurements correlating specific thickness and UVB absorption.[18]

The shorter UVC bands, as well as the even more energetic UV radiation produced by the Sun, are absorbed by oxygen and generate ozone in the ozone layer when individual oxygen atoms produced by UV photolysis of dioxygen react with more dioxygen. The ozone layer is especially important for blocking most UVB and the remaining portion of UVC that is not blocked by ordinary oxygen in the air.

Sunblockers

Sunglasses are essential for protecting the eyes from the harmful effects of ultraviolet (UV) radiation, which, though invisible, can cause significant ocular and periocular damage over time. Prolonged exposure to UV rays contributes to the development of various eye conditions, including cataracts, photokeratitis, and age-related macular degeneration, all of which can compromise vision and overall eye health.

Cataracts, characterized by clouding of the natural lens, are strongly linked to cumulative UV exposure, accelerating visual impairment if preventive measures are not taken. Similarly, the cornea and conjunctiva are susceptible to photokeratitis, an acute UV-induced inflammation that produces redness, pain, tearing, and temporary vision disturbances. Chronic exposure also increases the risk of macular degeneration, affecting the retina’s central region and critical for sharp, detailed vision. Moreover, the skin surrounding the eyes is particularly vulnerable to UV-induced damage, including premature aging, wrinkles, and skin cancers.

Not all sunglasses provide adequate protection. High-quality lenses must block 100% of UVA and UVB radiation. Frames designed for full coverage, including wraparound or larger styles, further reduce exposure from indirect rays. Polarized lenses enhance visual comfort by minimizing glare, providing additional protection in environments with reflective surfaces such as water, snow, or pavement. Children and adolescents are especially vulnerable, as their eyes are more sensitive to UV damage, and cumulative exposure early in life increases the likelihood of future ocular disease.

Sunglasses should be worn consistently, regardless of season or weather conditions, because UV radiation can penetrate clouds and reflect off surfaces, intensifying exposure. By selecting lenses that combine full-spectrum UV protection, adequate coverage, and optical quality, individuals can safeguard their visual health, reduce the risk of long-term eye disease, and protect the delicate skin surrounding the eyes.