Photometer for measuring intensity and rhodopsin distributions in intact eyes.

We describe a photometer that measures light transmitted through excised eyes. The instrument, an ocular transmission photometer, employs sensitive single photon-counting techniques, and its usefulness has been tested by the study of the absorbance of rhodopsin in retinal rod cells in situ. We find that absorbances of rat rods agree well with those predicted by microspectrophotometry without making corrections for cellular mosaics. Additional tests of the ocular transmission photometer show that (a) the instrument is sensitive to subtle differences in rhodopsin absorbance, known to exist in specific locations in the rat retina, and (b) using the rate of rhodopsin bleaching as the measure of intensity, we can determine the intensity distribution at several locations across the rat retina.