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M. Kojima, Y. Ishiba, Y. Iwai, K. Sasaki, H. Sasaki; Study of Reflected Light From the Back Side Lenses (Glasses or Sunglasses), as a Penetration Route Into the Eye. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4391.
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This study examined the ocular changes which occur when light is reflected from the back side of lenses, such as glasses or sunglasses.
Exp 1: Pigmented rabbits were irradiated with a reflected UV-B from a sunglass lens (the distance between the cornea and lens was 12 mm). The original UV-B dose was 3 J/cm2, which is equivalent to 5 hours of UV-B exposure in Kanazawa on a sunny autumn day. Anterior segment damage was evaluated by a slit-lamp with fluorescence staining 2 days after exposure. Lens epithelial damage was observed by the lens flat mounting technique. Exp 2: The lens reflections from 3 kinds of glasses (A: eye glasses, B: full-rim frame and C:wrap-around frame) set on a mannequin head were evaluated by 532 nm laser beam reflection. Exp 3: An ultraviolet sensor (Peak: 300 nm, a half width: 277-317 nm) was embedded in the ocular part of a mannequin. The mannequin wore 3 kinds of sunglasses (A, B, C), and irradiated with 500 W xenon light at 0°(frontal plane), 50°and 75° from the rear.
Exp 1: Lens reflection light from the sunglass lens induced corneal epithelial cell damage, but not lens epithelial cell damage. Exp 2: Lens back reflections from the 3 kinds of glasses entered the ocular area at the angle of 50°-85°. The angle at which the lens back side reflection entered the pupillary area was in A (76°) and B (74°). There was no backside reflection in C. Exp 3: The amount of reflected light from the back side lens of the glasses was 24% of the original light dose (3 J/cm2 at 90°). When the UV-B source was set at the temporal side of the mannequin (0°) and UV-B strength without sunglasses was 100%, the C sunglasses reduced UV-B exposure to 87%, but not A (101%) and B (111%). When UV-B exposure was from the rear at 50°, the highest UV-B penetration was observed with A (60 times higher than without sunglasses)>B (7 times)>C (3 times). When UV-B exposure was from the rear side at 75°, the highest UV-B penetration was observed with B (60 times) > A (12 times) > C (1.5 times).
This study suggests that light reflected from the back of lenses such as glasses, penetrates into the eye. It is possible to decrease this exposure by effectively cutting light from the rear.
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