June 2015
Volume 56, Issue 7
Free
ARVO Annual Meeting Abstract  |   June 2015
Luminance flicker-induced retinal venule dilation is improved by euglycemic clamp in type 1 diabetes
Author Affiliations & Notes
  • Jonathan Edward Noonan
    Ophthalmology, Centre for Eye Research Australia, Melbourne, VIC, Australia
  • Glenn M Ward
    Endocrinology and Diabetes, St Vincent's Hospital, Melbourne, VIC, Australia
    Clinical Biochemistry, St Vincent's Hospital, Melbourne, VIC, Australia
  • Ryan Man
    Singapore Eye Research Institute, Singapore, Singapore
  • Ecosse Luc Lamoureux
    Ophthalmology, Centre for Eye Research Australia, Melbourne, VIC, Australia
    Singapore Eye Research Institute, Singapore, Singapore
  • Footnotes
    Commercial Relationships Jonathan Noonan, None; Glenn Ward, None; Ryan Man, None; Ecosse Lamoureux, None
  • Footnotes
    Support None
Investigative Ophthalmology & Visual Science June 2015, Vol.56, 5951. doi:
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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)

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Abstract
 
Purpose
 

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.

 
Methods
 

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.

 
Results
 

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.

 
Conclusions
 

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.  

 
Figure 1. Mean relative arteriole dilations at baseline (solid line) and euglycemia (dashed line). Black bar indicates flicker.
 
Figure 1. Mean relative arteriole dilations at baseline (solid line) and euglycemia (dashed line). Black bar indicates flicker.
 
 
Figure 2. Mean relative venule dilations at baseline (solid line) and euglycemia (dashed line). Black bar indicates flicker.
 
Figure 2. Mean relative venule dilations at baseline (solid line) and euglycemia (dashed line). Black bar indicates flicker.

 
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