OPN4 and non-proliferative diabetic retinopathy: For example, a reduction in the baseline pupil size from 5.8 mm (the mean of the control group under dark-adapted conditions) to 3.6 mm (the mean of the moderate-severe NPDR group under dark-adapted conditions) would reduce the effective retinal illuminance of the melanopsin stimulus from 4.1 log Td to 3.7 log Td.