PURPOSE: As a consequence of an increasing prevalence of short-sightedness (myopia) in countries that have adopted western dietary patterns, it has been hypothesized that hyperglycaemia and hyperinsulinaemia induce myopia. The purpose of this study was to evaluate the relation between glycosylated haemoglobin (HbA(1c)), insulin dosage and myopia in diabetic patients. METHODS: All type 1 diabetic patients aged 16-26 years [mean age 22.0, standard deviation (SD) 2.9] attending the eye clinic at Steno Diabetes Center, Copenhagen, in 1995-1997 were included in the study (n = 393). The following data were collected from the medical records from baseline to 2005: age at diabetes onset, age at baseline, sex, weight, HbA(1c), insulin dosage, refractive error, visual acuity and ocular diabetes complications. Results: The prevalence of myopia [spherical equivalent (SE)