Basics of forward and backward scatter in the human eye lens

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Abstract

This presentation will treat basics of light scattering from the physical point of view, and as applicable to the human eye lens. The type of light scattering most easily recognized in ophthalmology is volume scattering, i.e. the more or less uniform lightness as seen in the slitlamp image. In fact this seeming uniformity derives from light scattering by a dense distribution of small particles. The ratio between backward and forward scatter strongly depends on particle size. Particles much smaller than wavelength scatter about equally in forward and backward directions; larger particles scatter (much) more strongly in forward direction. The particles dominating backward scatter in the human eye lens (towards the slitlamp, scheimpflug camera, etc.) are much smaller than wavelength. The particles dominating forward scatter have sizes of the order of wavelength. So, no direct link exists between slitlamp observation and hinder to the patient, as can be assessed with straylight. However statistically, the amounts of both types of scatterers can be linked. The less easily observed and understood type of scatter is surface scatter, e.g. from “Wasserspalten”. Optical bench study of human eye lenses on these phenomena will be presented.

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