Selective loss of S-cones in diabetic retinopathy

Abstract

Objective: To determine whether selective cone loss could explain the acquired 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 of retinas from 5 donors with diabetic retinopathy. For quantitative analysis, postmortem retinas were obtained from 13 human donors; 7 from patients with various durations and stages of diabetic retinopathy (4 background, 3 proliferative) and 6 controls. Enzyme histochemical analysis for carbonic anhydrase (CA) was used to distinguish L/M-cones (positive for CA) from S-cones (negative for CA). Cone topography was determined by sampling 360°from 0.1 to 1.5 mm of foveal eccentricity and along the horizontal meridians from 1.5 to 15.0 mm. Results: Rare cells in both the inner and outer nuclear layers of the diabetic eyes were positively labeled with the TUNEL method. The CA staining revealed incomplete and patchy losses of S-cones that were limited to the diabetic 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 percentage 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.