AbstractBackgroundWe previously reported a new diabetic strain of the Sprague‐Dawley rat, named the Spontaneously Diabetic Torii (SDT) rat. The purpose of the present study was to report the histologic and ultrastructural characteristics of diabetic retinopathy (DR) in a new animal model, the SDT rat.MethodsFifty‐three eyes of 43 SDT rats of various ages (35–82 weeks) were examined, of which 33 underwent histopathologic examination, 15 eyes fluorescein‐dextran microscopy, and five eyes the trypsin digestion method.ResultsOf the 33 eyes examined histopathologically, DR was identified in 20 eyes (61%). Large retinal folds mimicking diabetic tractional retinal detachment were observed in 20 eyes (61%). Retinal hemorrhages were seen in four eyes (12%). A neovascular fibrous membrane around the iris developed in five eyes (15%), of which two eyes had a massive anterior chamber hemorrhage. Of the 15 eyes examined by fluorescein‐dextran microscopy, an area of nonperfusion and/or extensive hyperfluorescence was observed in 12 eyes (80%). Of the five eyes examined using the trypsin digestion method, acellular capillaries and pericyte loss were observed in four eyes (80%). Of the 53 eyes, the previously mentioned retinal changes of DR were observed in 36 eyes (68%). The rats with DR (49–82 weeks; mean, 60 weeks) were older than the rats without DR (35–55 weeks; mean, 40 weeks) (p < 0.001).ConclusionLarge retinal folds mimicking tractional retinal detachment with extensive leakage of fluorescein around the optic disk was the most prominent finding of DR in SDT rats. Copyright © 2006 John Wiley & Sons, Ltd.