Ocular Optical Filtering

Abstract

Visual perception is initiated by the eye’s optics in the sense that the neural aspects of the visual process can only operate on the information that is presented to the nervous system. The varied ways in which this information is presented in the eyes of vertebrates and invertebrates raise questions about the consequences of the function of optical structures for vision. The purpose of this chapter is to review the effects of optical filtering on eye function emphasizing such unresolved issues, for example, as the function of optical filtering in the eyes of animals with high (suprahuman) visual acuity. Aspects of optical filtering will be reviewed commencing with the physical basis of transparency of the ocular media. The effects of interference and absorption filters will be examined. Polarization filters, which are covered by Waterman (this volume, Part B), and visual pigments, which have been recently reviewed by several authors in the Handbook of Sensory Physiology Vol. VII/I and Hamdorf (this volume), will be omitted. Filtering that results from the spatial arrangements and the physical properties of the photoreceptor cells will also be discussed. The unifying nature of this topic lends itself to a consideration of these factors independent of phylogenetic classification, and for this reason examples will be drawn freely from both the vertebrates and invertebrates.