Pupil size is regulated by the amount of visible light entering the eye . The absorption spectra of some sunglasses show high absorption of visible light but poor absorption in the ultra-violet range. This causes an increase in pupil diameter allowing more damaging UV light to reach the lens and retina than if no lenses were worn. Pupils were measured by photography for each of the 25 subjects wearing each of the nine test lenses. The absorption spectrum of each of the lenses was measured using a spectrophotometer and light levels reaching the eye were calculated. All nine of the tested lenses caused a significant increase in pupil area (p=0.009, protected t-test). Lenses with a relatively higher transmittance in the UV range therefore pose an increased risk of damage to the ocular tissues.
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