Variation in sensitivity, absorption and density of the central rod distribution with eccentricity

Purpose: To assess the human rod photopigment distribution and sensitivity with high spatial resolution within the central +/-15 degrees and to compar e the results of pigment absorption, sensitivity and rod density distributi on (number of rods per square degree). Method: Rod photopigment density dis tribution was measured with imaging densitometry using a modified Rodenstoc k scanning laser ophthalmoscope. Dark-adapted sensitivity profiles were mea sured with green stimuli (17' arc diameter, 1 degrees spacing) using a Tubi ngen manual perimeter. Sensitivity profiles were plotted on a linear scale and rod photopigment optical density distribution profiles were converted t o absorption profiles of the rod photopigment layer. Results: Both the abso rption profile of the rod photopigment and the linear sensitivity profile f or green stimuli show a minimum at the foveal center and increase steeply w ith eccentricity. The variation with eccentricity corresponds to the rod de nsity distribution. Conclusion: Rod photopigment absorption profiles, retin al sensitivity profiles, and the rod density distribution are linearly rela ted within the central +/-15 degrees. This is in agreement with theoretical considerations. Both methods, imaging retinal densitometry using a scannin g laser ophthalmoscope and dark-adapted perimetry with small green stimuli? are useful for assessing the central rod distribution and sensitivity. How ever, at present, both methods have limitations. Suggestions for improving the reliability of both methods are given.