The fractal geometry of proliferative diabetic retinopathy: implications for the diagnosis and the process of retinal vasculogenesis

Abstract

10 retinal vessel patterns with neovascularisation at or near the optic disk (NVD) from eyes of patients with diabetic retinopathy were compared with vascular patterns from 14 normal eyes. The vascular patterns were taken from low angle fundus photographs. After digitizing, the fractal dimensions were calculated by means of the density-density correlation function method. The fractal dimension was found to be significantly higher for vessel patterns with NVD [D = 1.845 ± 0.056 (m ± sd)] as compared with the normal control group (D = 1.708 ± 0.073) (p < 0.001). The fractal dimension of 1.8 appears to be a cutoff value. Higher values may indicate proliferative changes. Under these conditions the sensitivity of the method for the detection of NVD±Grade 3 in the Early Treatment Diabetic Retinopathy Study (ETDRS) grading system is 90%. The presence of such NVD in an eye is a “high risk characteristic” for severe visual loss, which requires panretinal laser treatment. Fractal analysis is therefore a possible new strategy for computer assisted “automated” detection and quantification of proliferative diabetic retinopathy. The fractal dimension of the new vessels suggests possible mechanisms involved in retinal vasculogenesis.