Abstract
Purpose :
Autoregulation of retinal blood flow may be impaired early in glaucomatous optic neuropathy. Measurement and comparison of autoregulation requires highly precise methods to determine retinal blood flow. We used EMAv, a novel method in which erythrocytes are labelled with Indocyanine Green (ICG) permitting precise measurement of absolute retinal blood flow, to study the difference between retinal arteriolar blood velocity in primary open angle glaucoma (POAG) and glaucoma suspect patients in response to oxygen-induced vasoconstriction.
Methods :
We prospectively enrolled thirteen human subjects and imaged 25 vessels of 19 eyes (9 POAG, 5 glaucoma suspect, 5 controls) by EMAv while breathing room air as well as 3 L/min of supplemental oxygen via nasal cannula in the same session. Angiograms were analyzed to determine average arteriolar erythrocyte velocity at baseline in room air and during oxygen supplementation. Velocity was measured in arterioles of 40-60 microns in diameter. Change in erythrocyte speed and percent change from baseline were calculated and compared between the groups. A generalized estimating equation (GEE) was used to account for multiple vessels measured in each person and compare the percent change from baseline between POAG and glaucoma suspect patients.
Results :
Mean age of the 13 subjects was 54.5 ± 11.8 years. Average erythrocyte speed was 6.73 ± 1.70 mm/s, 7.156 ± 2.42 mm/s, and 7.83 ± 2.78 mm/s in controls, glaucoma suspects, and glaucoma subjects respectively at baseline. After oxygen supplementation, this changed to 7.17 ± 2.00 mm/s, 7.19 ± 2.35 mm/s, and 7.10 ± 2.15 mm/s respectively. Percent change from baseline speed after oxygen supplementation showed a mean decrease of 6.67 ± 16.2% from baseline in glaucomatous eyes compared to a mean increase of 15.40 ± 18.58% in glaucoma suspect eyes (p < 0.01).
Conclusions :
Our results showed differing vascular responses to hyperoxemia between glaucoma and glaucoma suspect groups, suggesting impaired autoregulation of blood flow in glaucoma eyes as compared to glaucoma suspect in this modest sample of patients. Vascular dysregulation may occur early in glaucoma, and may ultimately serve as an early biomarker for improved diagnostics and treatment of disease.
This is a 2020 ARVO Annual Meeting abstract.