Assessing diabetic retinopathy using two-field digital photography and the influence of JPEG-comoression

Objective: To study the effectiveness of two digital 50degrees photographic fields per eye, stored compressed or integrally, in the grading of diabetic retinopathy, in comparison to 35-mm colour slides. Subjects and methods: Two-field digital non-stereoscopic retinal photographs and two-field 35-mm retinal photographs were made at the same time from patients visiting a diabetic retinopathy outpatient clinic. The digital images were stored integrally (TIFF-file) and in a compressed way (JPEG-file). Two ophthalmologists assessed the photographs in a masked fashion. The results were compared. The sensitivity and specificity for the detection of vision-threatening diabetic retinopathy were calculated, using only the grading of the most affected eye. The differences between the retinopathy gradings of the two kinds of photographs were analysed. Results: The agreement for the grading of DR compared to slides was good, both for the compressed and for the integrally stored images (kappa 0.63-0.68). The sensitivity for the detection of vision-threatening diabetic retinopathy using the JPEG-stored images was 0.72-0.74, specificity 0.93-0.98. The sensitivity for vision - threatening retinopathy detection using the integrally stored images was 0.86-0.92, specificity 0.93. Conclusions: Two-field digital retinal photography is effective in diabetic retinopathy grading and it can replace 35-mm retinal photography. Vision-threatening retinopathy can be detected on the images with reasonable to good sensitivity and specificity. An experienced grader should assess the images. The compression of the digital images seems to have some adverse effect on the detection of diabetic retinopathy.