Clues to duration of undiagnosed disease from retinopathy and maculopathy at diagnosis in type 2 diabetes: a cross-sectional study.

Aims: To extrapolate, from the proportion of subjects with observable retinopathy at diagnosis of type 2 diabetes mellitus in routine clinical practice, the mean duration of undiagnosed diabetes.

Methods: On 1 October 1999, there were 4313 patients with type 2 diabetes in the 41 participating practices in the Tayside region (registered with one of 166 GPs). 501 (12%; 95% CI 11 to 13%) patients were selected using a pseudo-random number allocation algorithm, and practice lists checked for recently deceased, non-residents (45 exclusions).