Ultra-Violet (UV) Protection
Only a limited range of wavelengths in the electromagnetic spectrum is perceived as ‘light’ by the human eye. Ultra-violet radiation lies just beyond the ‘blue’ end of the spectrum, and as such is invisible to us. The eye’s own cornea and the ozone layer surrounding the earth protect us from a large proportion of the sun’s UV, but the wavelengths closest to the visible spectrum (known as UVA) can reach the lens and retina inside the eye. Long-term exposure to UVA can cause cataract in the lens and contribute towards age-related macular degeneration of the retina (a progressive thinning of the retina in later life, causing some loss of vision).
Some spectacle lenses are naturally UV absorbing – all photochromic lenses (see above) and some high index lenses for example. Whilst untreated standard index optical plastic lenses only offer partial UV protection, they can be dye treated for full protection.