Study on the correlation between iris blood flow, iris thickness and pupil diameter in the resting state and after pharmacological mydriasis in patients with diabetes mellitus

Background To investigate whether iris blood flow and iris thickness at the iris smooth muscle region affect the pupil diameter at rest and after drug-induced mydriasis in patients with type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM). Methods T1DM patients and healthy children were recruited from the SCADE cohort. T2DM patients and healthy adults were recruited from patients undergoing cataract surgery at Shanghai General Hospital. Iris vessel density, pupil diameter (PD) and iris thickness were measured in both the resting and drug-induced mydriasis states. Iris vessel density was measured by optical coherence tomography angiography (OCTA), PD was measured by a pupilometer, and iris thickness at the iris smooth muscle regions were measured using anterior segment optical coherence tomography (AS-OCT). Results The study included 34 pediatric T1DM patients and 50 adult T2DM patients, both groups without diabetic retinopathy, and age-sex-matched healthy controls. At baseline, T1DM children and healthy children showed no differences in iris blood flow, iris thickness, or PD. However, the adult T2DM group exhibited higher vessel density at the pupil margin, thinner iris thickness at the iris dilator region, and smaller PD compared to healthy adults, with these differences being statistically significant ( P < 0.05). After pupil dilation, there were no changes in iris blood flow and PD in the T1DM group compared to healthy children, whereas the T2DM group showed a significantly smaller PD compared to healthy adults. Multivariate regression analysis revealed that in the T2DM group, glycated hemoglobin was an independent factor of PD after dilation (β=-0.490, p = 0.031), with no such factors identified in the T1DM group. Conclusion The insufficiently dilated pupil diameter after drug-induced mydriasis is correlated to the level of glycated hemoglobin among T2DM patients. Trial registration The registration number on the clinical trial website was NCT03631108.