Retinal microvascular signs | Definitions | References |
Background diabetic retinopathy | Presence of two or more microaneurysms in one eye | Ferguson et al20 |
Proliferative diabetic retinopathy (PDR) | A grading level at 60 or higher in one eye, or less than 60 but with panretinal photocoagulation scars consistent with laser therapy* | Ryan et al18 |
Diabetic retinopathy | A grading level greater than 10 (10 = no retinopathy)† | Kadoi et al19 |
Any retinopathy | Presence of any of the following lesions (not explicitly arteriolar in nature): microaneurysms, retinal haemorrhages, soft exudates, hard exudates, macular oedema, intraretinal microvascular abnormalities (tortuous intraretinal vessels), venous beading, new vessels at the disc or elsewhere, vitreous haemorrhage, disc swelling, or laser photocoagulation scars† | Wong et al,21 Baker et al22 |
Focal arteriolar narrowing (FAN) | An arteriole estimated to be 50 μm diameter or greater has a constricted area of 2/3 or less the width of proximal and distal vessel segments‡ | Wong et al,21 Baker et al22 |
Arteriovenous nicking (AV nicking) | A venule is constricted on both sides of its crossing under an arteriole in a specified region‡ | Wong et al,21 Baker et al22 |
Generalised arteriolar narrowing | Lowest 20th percentile of the sample arteriole-to-venule ratio (AVR) distribution measured on a continuous scale via a computer-assisted technique | Wong et al21 |
Arteriovenous ratio (AVR) | A ratio between the summarised calibre measurements of the arterioles (CRAE) with respect to the venules (CRVE)§ | Wong et al,21 Patton et al23 |
Central retinal arterial equivalent (CRAE) | Combined calibre measurements of individual arterioles coursing through a circular zone defined as between 0.5 and 1 disc diameter from the optic disc margin§ | Wong et al,21 Baker et al,22 Patton et al23 |
Central retinal venular equivalent (CRVE) | Combined calibre measurements of individual venules coursing through a circular zone defined as between 0.5 and 1 disc diameter from the optic disc margin§ | Wong et al,21 Baker et al,22 Patton et al23 |
Arteriolar branching coefficient (BC) | A ratio expressing the relationship between trunk vessel (W) and two branch vessels (w1 and w2) on vessel widths at arteriolar branching points: BC = (w12+w22)/w2 | Patton et al23 |
Arteriolar bifurcation angles (BA) | An angle (degree) measured at arteriolar branching points between the two branch arterioles | Patton et al23 |
Suboptimal branching coefficient | The degree of deviation of the BC from optimality (ie, a theoretical value of 1.26) | Patton et al23 |
Suboptimal angles | The difference of the degree of BA from optimality (ie, a theoretical and empirical value of 75°) | Patton et al23 |
*The Wisconsin Epidemiologic Study of Diabetic Retinopathy Classification and Grading System.24
†The Diabetic Retinopathy Study and the Early Treatment Diabetic Retinopathy study grading scale.25
‡The Modified Airlie House Classification of Diabetic Retinopathy.26
§Methods for evaluation of retinal microvascular abnormalities associated with Hypertension/Sclerosis in the Atherosclerosis Risk in Communities Study.27