Cone Photoreceptor Directionality and The Optical Density of the Cone Photopigments

Abstract

It is well known that the structure of the retina changes rapidly away from the center of the fovea. The cones become wider and shorter, and rods are present within the photoreceptor array. To examine the effect of changes in retinal structure with retinal eccentricity, the current paper compares the properties of the retinal photoreceptors as a function of retinal position. These measurements of the structural and functional properties of the foveal cone photoreceptors are important for both clinical and basic research questions. Clinically it is known that cone photopigment density is reduced by a number of disease processes. In addition the alignment of the cones towards the center of the pupil of the eye is also affected by a number of diseases1-4. In addition, a number of laboratories have begun investigating new techniques for imaging the photoreceptors in vivo5-6. These techniques typically require capturing the light exiting the eye and either correcting for the aberrations caused by the optics of the eye, or using coherent techniques that are less affected by the optics of the eye. These techniques require using a moderately large pupil (5-8 mm) to obtain the necessary resolution. However, we have shown that if light is collected over the entire pupil, then some of the light has been guided back out of the eye by the cone photoreceptor optics, and the other portion has been scattered. Since the directed light occupies only a portion of the pupil area, techniques dependent on light returning from the retina may be affected by variations in the waveguide properties of the cones with variations of retinal position.