Background: The aim of this study was to compare how diabetic retinopathy was detected from red-free digital images and colour transparencies. Methods: Two o phthalmologists graded two-field, nonster eoscopic, 60°red-free digital image s and colour transparencies utilizing an ETDRS-based grading scale, from 107 ma inly type 2 diabetic patients. The discordantly scored eyes were graded by the g raders together to obtain a consensus level of retinopathy for each method. The eyes with discordant consensus grading results were further graded using all ava ilable photographic material to reach a final consensus level of diabetic retino pathy. Intermethod variations were presented as percentages and using kappa (k) and weighted kappa (wk) statistics. The errors of the two consensus gradings wit h respect to the final consensus grading were compared using McNemar’s test. Re sults: For the colour transparencies there was an agreement between the individu al and the consensus grading results in 93%(k=0.90, wk=0.97) and 86%(k=0.79, w k 0.88) for grader 1 and grader 2. Corresponding figures for red-free digital i mages were 88%(k=0.83, wk=0.96) and 84%(k=0.78, wk 0.91). Agreement between me thods was obtained in 76/107 eyes (71%; k=0.58 and wk=0.79). In the 31 discorda ntly graded eyes the level of retinopathy was underestimated in 20/31 (64%) vs 7/31 eyes (23%) and overestimated in 1/31 (3%) vs 3/31 eyes (10%) from colour transparencies and red-free digital images, respectively. The error tendencies were significantly lower when using red-free digital images (p < 0.008). Concl usions: Red-free digital images are comparable with two-field colour transpare ncies in the identification of mild to moderate nonproliferative diabetic retino pathy.
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