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Jonathan Edward Noonan, Glenn M Ward, Ryan Man, Ecosse Luc Lamoureux; Luminance flicker-induced retinal venule dilation is improved by euglycemic clamp in type 1 diabetes. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5951.
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© ARVO (1962-2015); The Authors (2016-present)
Luminance flicker-induced retinal vasodilation is reduced in type 1 diabetes. Whether this relates to short-term glycemic control is unclear. We studied the effect of euglycemic clamp (normal glucose levels with insulin and glucose infusions) on these responses in people with type 1 diabetes.
12 otherwise healthy adult non-smokers with type 1 diabetes and no known complications were studied. Retinal imaging was performed with the Dynamic Vessel Analyzer (DVA, IMEDOS, Germany) after an overnight fast and repeated after 1 h of insulin infusion (6 pmol/kg/min; Actrapid, Novo Nordisk, Australia) and 30 min of euglycemia (6 ±1 mmol/l). Arteriole and venule calibers were measured in units (MU) under green light (130 cd/m2) at a rate of 25 Hz. Responses to 12.5 Hz luminance flicker were recorded from the mean of 3 consecutive intervals of 100 sec: 30 sec of constant light, 20 sec of flicker and 50 sec of constant light. Repeated tests used the same vessels. Within-subject changes in pre-flicker calibers, maximum relative dilations and area under the curve (AUC) during flicker were compared by ANOVA.
Subjects were (mean [standard deviation]) aged 25.5 (5.9) years with 11.0 (7.5) years of diabetes. From baseline to euglycemia, plasma glucose levels decreased from 8.4 (3.6) mmol/l to 6.1 (0.8) mmol/l (P = 0.004) and insulin levels increased from 64.6 (24.3) pmol/l to 333.6 (63.1) pmol/l (P < 0.001), respectively. Pre-flicker arteriole and venule calibers were unchanged between tests (both P > 0.05). From baseline to euglycemia, arteriole maximum dilations were 3.2 (2.4) % and 3.6 (2.4) %, while AUC were 31.2 (32.3) % x sec and 35.8 (32.1) % x sec, respectively (Figure 1; both P > 0.05). However, corresponding venule maximum dilations were 3.3 (3.4) % and 5.0 (4.1) % (P = 0.002), and AUC were 15.9 (44.1) % x sec and 44.6 (50.8) % x sec (Figure 2; P = 0.001), respectively.
Euglycemic clamp improves luminance flicker-induced retinal venule dilation in type 1 diabetes. Arteriole responses are not significantly affected. Glucose normalization with insulin may improve retinal blood flow regulation in type 1 diabetes.
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