Larger ON-pathway deficits in rod-dominated disease than cone-dominated disease

PURPOSE: ON-pathway deficits are associated with rod system dysfunction. Therefore, ON pathway function can potentially act as a surrogate marker of the rod system. Here, we have used a tablet-based application (iOS) called 'EyeSpeed' to assess the ON and OFF pathway deficits in patients with known retinal diseases. METHODS: 26 patients (19 male, 7 female) participated in the study. The patients were diagnosed with either rod-dominated disease [n=14; retinitis pigmentosa (12), rod monochromatism (2)] or cone-dominated disease [n = 12; Stargardt's disease (5) or cone dystrophy (7)] based on the fundus findings, history and/or electroretinographic findings. The participants were aged between 10- 46 years. The inclusion criteria were that near vision was N24 or better and absence of any other ocular disease. The participants task to identify number of black / white targets embedded in a binary noisy background. Outcome variables are reaction time, accuracy and performance index [accuracy*(1/reaction time)]. RESULTS: The mean difference in reaction times (dark - light) for rod-dominated disease [Mean (SEM): -1.94s (0.43) was significantly higher than cone-dominated disease [ [-0.65s (0.23)]; unpaired t-test, p=0.019]. However, mean differences between dark and light targets in accuracy and performance index were not significantly different between the two groups. CONCLUSIONS: ON pathway deficits in rod-dominated disease is prominent compared to the OFF-pathway deficits.