A New Method for Semi-Automated Measurement of Microaneurysms Formation Rate From Color Fundus Photographs in Diabetic Retinopathy

Abstract

Purpose: : To assess the reliability of microaneurysm (MA) formation rate, computed from color-fundus photographs, to evaluate diabetic retinopathy (DR) in patients with diabetes type 2 and nonproliferative retinopathy.

Methods: : To assist the grader on earmarking MAs on color-fundus photographs, a new method (MA Tracker) was developed which performs MA counting taking into account the specific location of each MA by registering its exact coordinates in the eye’s fundus. Color-fundus photographs are first enhanced by applying a Principal Component Analysis and thereafter co-registered to the baseline image. This co-registration procedure allows to identify each MA based on its exact location. New MAs are therefore identified if they appear in any location for the first time, therefore allowing MA formation rate to be computed (number of new MA per year).To compute the reliability of the MA formation rate in patients with nonproliferative retinopathy, 3 different graders were asked to earmark MAs on the same set of 235 color-fundus photographs (shown at random), from 47 type 2 diabetic patients followed for 2 years at 6-months intervals. The inter-grader agreement for MA earmarking was assessed using the Intraclass Correlation Coefficient (ICC) and the Bland-Altman plot.

Results: : When comparing MAs earmarked by the 3 different graders, the inter-grader agreement is weak (38% of the MAs earmarked in each eye/visit).However, a very good agreement was found between the 3 graders for the MA formation rate using the MA Tracker (ICC=0.966; 95%CI=[0.945; 0.980]).

Conclusions: : MA formation rate obtained from color-fundus photographs using the MA Tracker show a very good reliability between different graders and may be used as an indicator of MA turnover in the initial stages of DR.

Keywords: retina • diabetic retinopathy • imaging/image analysis: clinical