Induced movement of receptor alignment toward a new pupillary aperture

Bonds and MacLeod (1978) reported on an individual whose receptors, as measured by the peak of the Stiles-Crawford function, were oriented in the direction of a traumatically displaced pupil. In an attempt to demonstrate that this orientational response is caused by an active alignment process and not simply a result of passive forces due to the traumatic ocular injury, we attempted to influence receptor alignment in the same eye by artificially creating a centered pupil. This was accomplished by placing on the subject's dilated eye a soft contact lens containing a centered 2mm artificial pupil. Receptor alignment (inferred from the entrance pupil location of the peak of the Stiles-Crawford function) significantly changed (0.8 mm) in the direction of the "new pupil" over a time course of 5 days. This alignment persisted for as long as the pupil was worn (1 month). With removal of the artificial pupil, the receptor alignment returned to its original eccentric orientation in 5 days. The results indicate that an active phototropic mechanism significantly influences receptor alignment toward the pupillary aperture.