Vertebrate receptor optics and orientation.

Vertebrate photoreceptors act as optical waveguides. They exhibit directionality, non-uniform distribution of energy within and immediately about the receptor, etc. Photolabile pigment absorption favors light traveling axially down the receptor. Clearly these properties influence response of the transducer. Retinal receptors, rods and cones, are aligned normally with a point approximating the center of the exit pupil of the eye. Taken together, these findings suggest that a prime role of receptor optics is to favor acceptance of the pertinent visual stimulus passing through the pupillary aperture and to inhibit stray light noise contained in the integrating sphere-like eyes. Many intriguing problems remain to be resolved. It is necessary to relate the properties of the receptor as a waveguide to determinations of directional sensitivity of the retina (Stiles-Crawford effects), and in particular, to understand mechanisms leading to fine receptor alignment. There must also be a pathology of receptor orientation--a science still in its infancy.