CHROMATIC-CONTRAST THRESHOLD IMPAIRMENT IN DIABETES

A prospective study was carried out to investigate acquired colour-vis ion deficits in diabetics using an automated, computer-controlled, cat hode-ray-tube based test of chromatic contrast, Chromatic-contrast thr esholds estimates were measured along both a red/ green (constant S-co ne) confusion axis and a tritan (constant Mn-cone) confusion aids for 305 eyes of 305 diabetics, The diabetic data were partitioned into gro ups based on a clinical categorisation of retinopathy, The diabetic da ta were compared with both age-matched and 'lens-equated' control data obtained from a bank of 347 normal subjects, Further analysis of diff erences between diabetic-status groups was performed, Associations bet ween chromatic contrast threshold estimates and age, duration of disea se, and severity of both macular oedema and ischaemia were investigate d, The diabetic group was found to have significantly reduced chromati c-contrast threshold estimates when compared with normal controls, eve n in the absence of retinopathy, This reduction in chromatic contrast was predominantly tritanopic in nature, Interestingly, no reduction in red/green chromatic-contrast threshold estimate was found in diabetic s without retinopathy, The tritan deficit seen in diabetics without re tinopathy was strongly correlated with duration of disease, but when a djustments were made to account for the effects of duration-dependent lens yellowing, the tritan deficit was no longer apparent, A correlati on between both the severity of macular oedema and severity of ischaem ia with chromatic-contrast loss was established, Acquired reductions i n both red/green and tritan chromatic-contrast threshold estimates see n in diabetics are strongly correlated with the severity of retinopath y, The results provide evidence that the specific tritan deficits seen in diabetics can be explained by the effects of lens yellowing rather than by selective damage of the blue cone system as has been hypothes ised by other groups, The results provide support for the potential us e of automated CRT-based tests of colour vision in diabetic retinopath y screening protocols.