Methodology for retinal photography and assessment of diabetic retinopathy: the EURODIAB IDDM Complications Study

Summary We present the methodology for 45 retinal photography and detail the development, application and validation of a new system of 45 field grading standards for the assessment of diabetic retinopathy. The systems were developed for the EURODIAB IDDM Complications Study, part of a European Community funded Concerted Action Programme into the epidemiology and prevention of diabetes (EURODIAB). Assessment of diabetic retinopathy was carried out centrally by a trained reader of colour retinal photographs using the newly-developed system. The system proved to be acceptably accurate, repeatable and relatively simple to apply. It compared well with the recognised gold standard 7-field 30 stereo photography (assessed using a modified Airlie House classification scheme), against which the new system was validated in a series of 48 eyes. Selection was as a stratified random sample based on clinical retinopathy status: 5, no retinopathy; 25, non-proliferative retinopathy; 16, proliferative or photocoagulated; plus 2, eyes with potentially confounding lesions (vein occlusion). Simple presence of retinal lesions was correctly detected by both systems in 43 of the 48 eyes, giving 100% agreement on detection. Both systems correctly identified the two known cases of confounding vein occlusion. In eyes with diabetic retinopathy (n=41), when severity was expressed in three groups: mild background, moderate/severe background and proliferative/ photocoagulated, at least one grader (out of five) using the new system matched the verified results in 38 out of 41 (93%) eyes and three or more graders matched in 31 (76%) eyes. Individually the five graders' 2-field allocations agreed well with the verified levels (median number of agreements 37, range 28–43). Repeatability was assessed by measures of within and between observer variation using randomly selected samples of 10% (n=252 eyes) and 5% (n=123 eyes) of the main study, respectively, expressed as a resultant kappa value for chance-corrected proportional agreement. Within observer assessment yielded a kappa of 0.85 and between observers a value of 0.83; indicating very good agreement for both measures. The method is particularly useful for large epidemiological studies, in which participating centres have a limited experience in retinal photography.Abbreviations HMA Haemorrhages and microaneurysms - ETDRS Early Treatment Diabetic Retinopathy Study