Diabetic Retinopathy Severity Scale: Decoding the Numbers

The Diabetic Retinopathy Severity Scale (DRSS) is commonly encountered in clinical trial reports and research literature. Trainees are often puzzled by the use of seemingly irregular numerical labels such as 10, 20, 35, 43, 47 and 53 to describe disease severity. These numbers neither follow a linear progression nor represent uniformly spaced severity intervals. What appears to be arbitrary numbering is, in fact, a deliberate design choice. This article explains the historical evolution and rationale underlying the non-linear numbering of the DRSS, with emphasis on its origin as a photographic grading system developed primarily for research applications.