The study photographs were retrieved retrospectively from the photographic archives of all 184 patients who attended the Steno Diabetes Center Retinopathy Service during two randomly selected consecutive weeks of November 1999. Inclusion criteria per patient were an established history of diabetes mellitus, type 1 or type 2, and availability of at least one macula-centered (center of fovea within 10° of the center of the photographic frame) color fundus photograph from at least one eye. The slides were routinely mounted in legal-sized plastic pockets, from which the slide in the upper left pocket was systematically chosen. This slide represented the left slide of a stereo pair. Exclusion criteria per eye were previous photocoagulation or surgical treatment of diabetic retinopathy or other vitreoretinal disease and media opacities precluding adequate visualization of the fundus by fundus photography, as evaluated at the routine screening sessions.
From the photographic archives, 365 macula-centered photographs obtained in eyes of the 184 patients were retrieved. Thus, three patients were represented by photographs from only one eye each because the fellow eye was blind. Among the remaining 365 eyes, four eyes in four patients had previously been exempted from screening because media opacities precluded adequate visualization of the fundus (two eyes with cataract, one eye with vitreous hemorrhage, and one eye with asteroid hyalosis). Photocoagulation treatment had been performed in both eyes in 43 patients and in one eye in 12 patients. Three eyes in three patients were not included because of decentration of the photographs. One fundus photograph from each of the remaining 260 eyes in 137 patients was included in the study. It follows that 14 of the 137 patients were represented by one eye, because photocoagulation had been applied in the fellow eye (eight patients), the patient had one blind eye (one patient), the photographs of the fellow eye were decentered (two patients), or the eye had previously been exempted from photographic screening because of media opacities (three patients).
The Steno Diabetes Center serves more than 4000 patients with type 1 and more than 1000 patients with type 2 diabetes from the greater Copenhagen area. More than 80% of the patients are systematically screened for diabetic retinopathy by fundus photography under a predefined clinical protocol that was established 12 years before the initiation of the study.
The present study was entirely retrospective and complied with the tenets of the Declaration of Helsinki. The study did not involve patients or biological samples and as such did not require institutional review under Danish law.