Electroretinogram (ERG) sensitivity and phagosome frequency in the normal pigmented rat.

Normal adult pigmented rats, born and raised in cyclic light for 25- to 27 days and then placed in darkness for up to 24 hr, showed an inverse relation between electroretinogram (ERG) sensitivity and phagosome frequency in the pigment epithelium over the course of a day. Linear regression revealed that a two-fold increase in the frequency of large phagosomes was associated with approximately a one-third decrease in ERG sensitivity. The observed 37-40% decline in ERG sensitivity 1.5 hr after expected light onset was significantly greater than what would be expected from the measured 11% shortening of rod outer segments at that time of day. Possible explanations for this disparity are considered.