Identification of diabetic retinopathy by stereoscopic digital imaging via teleophthalmology: a comparison to slide film

BACKGROUND: Diabetic retinopathy is a leading cause of vision loss in North America. We compared mydriatic seven-field stereoscopic digital imaging to 100 ASA slide film photography for the identification of diabetic retinopathy via teleophthalmology. METHODS: Patients from a northern Alberta community with diabetes mellitus diagnosed by a physician were asked to participate in a teleophthalmology pilot project. Patients were enrolled at four different times between October 1999 and June 2000. Seven 30 degree fields of the retina were photographed with both slide film and digital imaging (resolution 2008 x 3040 pixels) through a dilated pupil. Slide film was developed and reviewed in a masked fashion by a retinal specialist. Digital images for each patient were transmitted by satellite to Edmonton and analysed a minimum of 2 months after the original slide film. Retinal abnormalities were graded with the use of the Early Treatment Diabetic Retinopathy Study extension of the modified Airlie House classification. We calculated the sensitivity and specificity of digital imaging for the identification of features of diabetic retinopathy as seen on slide film. Pearson's correlation coefficient was also calculated. RESULTS: A total of 121 patients (241 eyes), of whom 114 (94.2%) had non-insulin-dependent diabetes, participated in the study. The average duration of diabetes was 8.5 years. Of the 121 patients 57 (47.1%) had diabetic retinopathy, 12 (9.9%) had clinically significant macular edema and 2 (1.6%) had neovascularization. Pearson's correlation coefficient for the presence of retinopathy between slide film and stereoscopic digital imaging was 0.92 for microaneurysms, 0.80 for hemorrhages, 0.45 for intraretinal microvascular abnormalities, 0.32 for venous beading, 1.00 for neovascularization of the disc, 1.00 for neovascularization elsewhere in the retina and 0.97 for clinically significant macular edema (p < 0.001). The correlation between the two techniques for severe nonproliferative diabetic retinopathy (NPDR) was 0.86 and for high-risk proliferative diabetic retinopathy 1.00 (p < 0.001). INTERPRETATION: Stereoscopic digital imaging has a high level of correlation with slide film for the identification of most features of diabetic retinopathy, including microaneurysms, hemorrhage, severe NPDR, high-risk proliferative diabetic retinopathy and clinically significant macular edema.