The corneal sensation of diabetic patients undergoing pan retinal photocoagulation for the treatment of proliferative retinopathy was measured using the Cochet-Bonnet aesthesiometer. Insulin dependent and non-insulin dependent diabetics both showed significantly decreased corneal sensitivity, and there was no significant change following pan-retinal photocoagulation. Insulin dependent diabetics with proliferative retinopathy had been diagnosed for a significantly longer period than non-insulin dependent diabetics, but had better corneal sensitivity than the latter group. Male patients were more likely to have brown irides, whereas there was a preponderance of blue irides amongst the females. Patients with blue irides also had significantly lower sensitivity than patients with brown irides. The results are discussed.