Selective loss of S-cones in diabetic retinopathy

Objective: To determine whether selective cone loss could explain the acqui red tritan-like color confusion found in diabetic retinopathy. Methods: Terminal deoxynucleotidyl transferase-mediated biotin-deoxyuridine triphosphate nick end labeling (TUNEL) was employed on paraffin sections o f retinas from 5 donors with diabetic retinopathy. For quantitative analysi s, postmortem retinas were obtained from 13 human donors; 7 from patients w ith various durations and stages of diabetic retinopathy (4 background, 3 p roliferative) and 6 controls. Enzyme histochemical analysis for carbonic an hydrase (CA) was used to distinguish L/M-cones (positive for CA) from S-con es (negative for CA). Cone topography was determined by sampling 360 degree s from 0.1 to 1.5 mm of foveal eccentricity and along the horizontal meridi ans from 1.5 to 15.0 mm. Results: Rare cells in both the inner and outer nuclear layers of the diabe tic eyes were positively labeled with the TUNEL method. The CA staining rev ealed incomplete and patchy losses of S-cones that were limited to the diab etic retinas. Statistically significant reduction in the density of S-cones was found at nearly all foveal eccentricities from 0.1 mm to 15.0 mm. This was not the case for the L/M-cones. On average, for all locations, the per centage of S-cones compared with L/M-cones was decreased by 21.0% +/- 3.4 % with respect to the controls. Conclusion: The S-cones selectively die in diabetic retinopathy. Clinical Relevance: Selective loss of S-cones may contribute to the tritan- like color vision deficit seen in patients with diabetic retinopathy.