The absorption of polarized light by vertebrate photoreceptors

A physiologically realistic model has been constructed for a theoretical study of the mechanisms by which the vertebrate visual system absorbs linearly polarized light. Using a 4x4 matrix technique, analytic solutions to Maxwell's equations have been deduced for rod and cone photoreceptors, allowing calculation of the absorbance as a function of wavelength for a variety of illumination geometries. With the use of experimentally measured optical parameters the calculated absorbance spectra show excellent agreement in both magnitude and form with microspectrophotometric data. Moreover, failing to correct for the true nature of reflection or scattering in the sample, results in the elevated absorbance commonly seen at shorter wavelengths in experimental measurements. Finally, calculated dichroic ratios also accurately predict experimental results, mirroring the differences seen between rods and cones. (C) 2004 Elsevier Ltd. All rights reserved.