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Thomas J T P Van Den Berg; Scattering extinction of human eye lenses and straylight. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5813.
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© ARVO (1962-2015); The Authors (2016-present)
It is well established that disability glare derives from the optical effect of light scattering in the human eye media, causing the visual effect of ocular straylight, and the associated desensitization of the eye. Light scattering removes part of the light from the optical projection on the retina. In light scattering physics this removal of light is called scattering extinction, and adds to the more well-known absorption extinction. In the present study we derived from earlier measurements on light scattering by human eye lenses the extinction values and correlated those with the straylight values as they can be measured clinically as log(s) with the C-Quant from Oculus.
Light scattering was measured for a number of discrete scatter angles and wavelengths for 15 human eye lenses extracted from donor eyes, aging 43 to 82 years. The data were fitted with scatter functions from physical theory to derive complete scatter characteristics, and to calculate the full amount of light lost to scattering. The extinction values found were correlated with the straylight parameter s for the same lenses, corresponding to the clinical measure.
The light scattering characteristics of 14 of the lenses showed to correspond to particle distributions with mean average radius of 692 nm ± 227 nm s.d. One 70 year old very cataractous lens showed an average radius of 589 nm. The straylight values at a wavelength of 602 nm differed in total by 2.24 log unit, but with little correlation to average particle size (r=-0.06). Extinctions were calculated for a wavelength close to the top of the visual spectrum (561 nm). It varied from 2.5% to 20.7% for 14 lenses, and was 33.9% for the most cataractous lens. Correlation with the straylight value yielded extinction=0.01007s. Part of the scattering corresponded with Rayleigh type scattering, and the respective extinctions were 1.4% to 25.1% for 14 lenses, and 43.3% for the most cataractous lens.
For aged human eye lenses, scattering extinction removes a significant part of the light from the projection to the retina. For relatively normal lenses, this can be up to 30% in the middle of the visual spectrum. For one rather cataractous lens a loss of 77.2% was found. In vivo, extinction for the forward scatter component can be estimated using a straylight measurement as 0.01007x10log(s). However, also a significant amount of extinction from Rayleigh scatter must be added.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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