Aqueous humor dynamics in patients with diabetes mellitus

We measured aqueous dynamic variables in subjects with diabetes mellitus and correlated them with severity of retinopathy and metabolic control to determine whether diabetes affects the anterior circulation of the eye as it affects the posterior (retinal) circulation.

Sixty-one subjects with diabetes mellitus type 1 and 60 subjects with diabetes mellitus type 2 were recruited from the active practice of the Mayo Clinic. Thirty-two normal subjects, divided by age into two overlapping groups of 20 each, served as contemporaneous control subjects. The diabetic subjects were stratified into four groups according to severity of retinopathy. Aqueous humor flow was measured by clearance of topically applied fluorescein with a spectrofluorophotometer; outflow facility was measured by tonography; and intraocular pressure was measured by applanation tonometry.

In type 1 diabetics, the mean intraocular pressure was slightly greater (14 +/- 3 mm Hg), compared with control subjects (12 +/- 2 mm Hg [P = .002]), while aqueous humor flow was slightly less (2.5 +/- 0.6 microliter/min), compared with control subjects (2.9 +/- 0.5 microliter/min [P = .023]). In type 2 diabetics, the intraocular pressure was 14 +/- 3 mm Hg, which did not differ from that of control subjects (14 +/- 3 mm Hg [P = .258]). Aqueous humor flow in type 2 diabetics (2.5 +/- 0.7 microliter/min) did not differ significantly from that of the control group (2.5 +/- 0.7 microliter/min [P = .961]). Tonographic facility of outflow was not significantly different in type 1 and type 2 diabetics and the control subjects. There was no significant correlation in aqueous humor flow, intraocular pressure, or tonographic facility of outflow to severity of retinopathy or hemoglobin A1c in either type 1 or type 2 diabetics.

The dynamics of aqueous humor are not affected to any clinically significant extent in the early or middle stages of diabetic retinopathy. However, there is a tendency toward less aqueous humor flow in the advanced stages of retinopathy.