Fig. 1
From: Retinal vessel diameters and reactivity in diabetes mellitus and/or cardiovascular disease
Sample image showing measurement area for static retinal vessel evaluation. Central ring denotes the diameter of the disc (1 DD), the second and third circle are each ½ DD separated to create a ½ DD wide concentric ring segment around the optic nerve head. This ring segment is highlighted here in yellow to illustrate the area in which retinal arterial and venous calibres are measured to calculate central retinal artery and vein equivalents (CRAE and CRVE)