Purpose: Local variations in refractive index are an important physical cause of light scattering in the lens. The goal of this study was to further add to the understanding of the process of light propagation in the lens by directly measuring local variations in refractive index by phase contrast microscopy. Methods: Refractive index was estimated by immersion refractometry. Cryo-sections of quick frozen human donor lenses were embedded in a graded series of bovine serum albumin solutions, and in immersion oil. Results: Superficial cortical fiber membranes proved to have a refractive index considerably above values given for cytoplasm at the same location. Nuclear fiber membranes have a refractive index of the same order as given in the literature for nuclear fiber cytoplasm. Conclusion: The large difference in refractive index between fiber membranes and cytoplasm in the lens cortex may be important for optical function and transparency of the lens. Support: Marie Curie Fellowship of the European Community program Quality of Life (QLK6-CT-1999-51159).
It is concluded that sunglasses shall block UVR and toxic blue light, allow transmittance of signal light and bring luminous intensity behind the filters to a comfortable level. It was found that some commercially available sunglasses, apart from one pair of photochromatic dark state lenses tested, block ultraviolet radiation (UVR) adequately. Further, it was found that it is possible to block the toxic blue radiation without interfering substantially on blue signal light perception. However, none of the sunglasses tested blocked the toxic blue light enough.
The penetration of 300 nm ultraviolet radiation (UVR) in the anterior cortex of the crystalline lens was 0.45 mm, penetration being expressed as the distance attenuating the transmittance to 1/e2. The estimation is based on measurement of in vivo inactivation of lactate dehydrogenase (LDH) due to in vivo exposure to UVR 300 nm. The inactivation of LDH was independent of the latency interval after the exposure within 0 - 6 h. There was a 30 - 40% inactivation of LDH in the cornea that dropped to 0% in the inner anterior cortex. The currently described method allows spatially resolved measurement of the in vivo dose of UVR 300 nm within the cornea and the crystalline lens.
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