Spatial information capacity of eyes: roles of Na+ channels and photon noise in photoreceptor.

The spatial information capacity of the human eye for photopic vision has been determined taking into account the intensity response function of the photoreceptor. It has been found that spatial information capacity increases with the mean luminance upto a certain value of mean luminance and after that it starts decreasing. The decrement occurs below the damage threshold. These results are in agreement with the reported experimental observations. It has been concluded that the limited number of Na+ channels in the photoreceptor outer segment and the photon noise are responsible for the fall in the information capacity below the damage threshold.