JPEG compression of stereoscopic digital images for the diagnosis of diabetic retinopathy via teleophthalmology

Abstract

Background: Canada's vast size and remote rural communities represent a significant hurdle for successful monitoring and evaluation of diabetic retinopathy. Teleophthalmology may provide a solution to overcome this problem. We investigated the application of Joint Photographic Experts Group (PEG) compression to digital retinal images to determine whether JPEG compression could reduce file sizes while maintaining sufficient quality and detail to accurately diagnose diabetic retinopathy.

Methods: All 20 patients with type 2 diabetes mellitus assessed at a 1-day teleophthalmology clinic in northern Alberta were enrolled in the study. Following pupil dilation, seven 30 degrees fields of each fundus were digitally photographed at a resolution of 2008 x 3040 pixels and saved in uncompressed tagged image file format (TIFF). The files were compressed approximately 55x and 113x their original size using JPEG compression. A reviewer in Edmonton randomly viewed all original TIFF images along with the compressed JPEG images in a masked fashion for image quality and for specific diabetic retinal pathology in accordance with Early Treatment Diabetic Retinopathy Study standards. The level of diabetic retinopathy and recommendations for clinical follow-up were also recorded. Exact agreement and weighted kappa statistics, a measure of reproducibility, were calculated.

Results: Exact agreement between the compressed JPEG images and the TIFF images was high (75% to 100%) for all measured variables at both compression levels. Reproducibility was good to excellent at both compression levels for the identification of diabetic retinal abnormalities (K = 0.45-1), diagnosis of level of retinopathy (kappa = 0.73-1) and recommended follow-up (kappa = 0.64-1).

Interpretation: The application of JPEG compression at ratios of 55:1 and 113:1 did not significantly interfere with the identification of specific diabetic retinal pathology, diagnosis of level of retinopathy or recommended follow-up. These results indicate that JPEG compression at ratios as high as 113:1 has the potential to reduce storage requirements without interfering with the accurate and reproducible teleophthalmologic diagnosis of diabetic retinopathy. This pilot project demonstrates the potential for JPEG compression within a digital teleophthalmology viewing system.