Objective: To investigate the processing of spectral information by chromatic and achromatic pathways in patients with diabetes mellitus with early diabetic retinopathy and compare the results with those of normals.

Method: The sensitivity to a foveally fixated 1° pseudomonochromatic flashed circular target seen against a 3 log Troland 10° white background was measured as a function of wavelength for target flash durations of 500ms and 20ms. The responses to the long and short flashes are dominated by chromatic and achromatic mechanisms respectively. Fourteen diabetic patients and ten control subjects of similar ages performed the test. The threshold of perception of each stimulus was measured using a randomly interleaved double staircase for 10 wavelengths in the range 450nm to 660nm.

Results: The results show a significant reduction in the sensitivity of the diabetic subjects to the 500ms flash at all wavelengths and to the 20ms flash for all bar 560nm and 660nm. The shape of the 20ms flash curve was the same in both groups. The shape of the 500ms flash sensitivity curve for the normals showed peaks in sensitivity at 525nm and 612nm and a rise at 450nm. However in the diabetic patients the 525nm peak and the 450nm rise were absent. Neither of these findings could be accounted for by changes in the ocular media of the patients with diabetes.

Conclusions: The results indicate a reduction in the spectral sensitivity in diabetes, which is consistent with reduced sensitivity in both chromatic and achromatic mechanisms, although the chromatic mechanism appears to be more severely affected.

King-Smith PE, Carden D. Luminance and opponent-colour contributions to visual detection and adaptation and to temporal and spatial integration. J. Opt. Soc. Am. 1976;66(7):709-717.