Dynamic Pupillometry in Type 2 Diabetes: Pupillary Autonomic Dysfunction and the Severity of Diabetic Retinopathy

Autonomic dysfunction may precede the microvascular changes that characterise diabetic retinopathy. The aim of this pilot study was to measure and compare pupillometry indices in type 2 diabetes (T2DM) patients - with and without diabetic retinopathy - and in healthy, age-matched controls.

Two hundred and eleven participants with T2DM aged 45-80 years were recruited from Dunedin Hospital Eye Department, Dunedin, New Zealand. They were categorised into three groups - no, mild/moderate, or severe diabetic retinopathy. Seventy age-matched, diabetes screen negative control participants were recruited from the Dunedin city community. Dynamic pupillometry was performed using an infrared pupillometer. The main outcome measures were maximum constriction velocity, average constriction velocity, absolute constriction amplitude, relative reflex amplitude, average dilation velocity and 75% re-dilation (recovery) time. Outcome measures were compared between study groups using the Kruskal-Wallis nonparametric test (with Dunn's multiple comparison post-test).

Pupillary parasympathetic function differed between groups. Maximum constriction velocity (p <0.001) and average constriction velocity (p <0.001) were slower, and absolute constriction amplitude (p <0.001) and relative reflex amplitude (p <0.05) were lower in the three diabetes groups compared with controls. There were no significant differences in pupillary sympathetic function between the four groups for re-dilation time, but the diabetes groups had significantly slower average dilation velocity times.

Pupillary light reflex is significantly impaired with diabetic retinal neuropathy, before clinically observable signs of diabetic retinopathy. Dynamic pupillometry may be a cheap, clinically relevant test, but sensitivity and specificity need to be determined before utilising as a screening tool for diabetic retinopathy.