Evidence for non-selective colour channel involvement in diabetic eyes especially after laser treatment

PURPOSE: We consider the hypothesis that proliferative diabetes produces selective lossof colour channels. We also consider the possibility that laser treatment for this condition does not affect macula function. METHODS: We tested for the possibility of a selective colour channel involvement in 35 eyes of 33 cases of proliferative diabetes by considering the outcomes of saturation and hue testing before and after pan-retinal photocoagulation (PRP). Saturation testing was achieved with the Sahlgren Saturation Test (SST) and hue testing was via the Farnsworth-Munsell 100 (FM100) hue test. Our results were compared to a recent model1 that was developed to predict the saturation processing of diseased eyes. RESULTS: All diabetic eyes with normal hue (FM100) scores passed the saturation test (SST). Most pre-treatment eyes (29 of 35 or 83 per cent) failed the FM100 hue test but only 16 of 35 (46 per cent) failed the saturation test. Following laser treatment, 97 per cent of eyes were abnormal on the FM100 hue test but only seven per cent failed the saturation test. CONCLUSION: Untreated diabetic eyes with proliferative retinopathy show losses of both hue and saturation processing. The nature of this relationship is consistent with that modelled assuming moderate and asymmetric non-selective losses in both chromatic and luminance channels. Laser treatment (PRP) appears to produce a paradoxical normalisation in saturation percepts in the presence of deteriorating hue scores. We find that this outcome is consistent with a more severe generalised reduction of sensitivity in both the chromatic and luminance processes and conclude that pan-retinal photocoagulation results in these unexpected macula changes.