Studies on the retina of the gecko Coleonyx variegatus. 3. Photoreceptor cross-sectional area relationships.

The percentage of the retina occupied by outer segments in cross section was found to be 53%. Based on these measurements, the percentage of light absorption for the total retina was calculated to be 40% which agreed better with the value of 39% given for the cat allowing for the effect of the tapetum than with the value of 68% for a nocturnal gekkonidean. This would indicate the increased outer segment length gives Coleonyx at least the same advantage as the tapetum of the cat. Errors such as tissue shrinkage, convergent lens effect of the inner segment, and measuring errors, which would tend to increase the value of 40%, were discussed and approximated.