Diabetic retinopathy (DR) is a leading cause of blindness in people of working age in developed countries. DR is characterized by lesions of the retinal microvasculature. This paper describes a technique for visualizing the changes which occur in retinal pathology over a 1 year interval. Pairs of retinal images of the same eye were acuired 12 months apart within a DR screening programme. The images were normalized, registered and subtracted to generate a contrast-enhanced difference image displaying changes in retinal appearance. The normalization factor and registration error were quantified for 104 pairs of retinal images. (c) 2006 Elsevier Ltd. All rights reserved.