Inter-visit repeatability of retinal blood oxygen saturation and total retinal blood flow measurements under conditions of hypoxia, hyperoxia and normoxia in healthy individuals

Abstract

Purpose: The development of a prototype Doppler spectral domain optical coherence tomography (SD-OCT) blood flow technology and hyperspectral retinal imaging represent a significant advance in ocular imaging capabilities. In this study, SD-OCT derived total retinal blood flow (TRBF) measurements as well as the oxygen saturation (SO₂) of major retinal vessels were validated and calibrated in human volunteers using a novel and exact provocation technique (RespirAct) that allows the precise control of the end-tidal partial pressure of oxygen (P_ETO₂). We hypothesis that an increase in arterial O₂ tension will decrease the TRBF and increase the retinal oxygen saturation; and vice versa should occur when arterial O₂ tension decreases. Between visit repeatability of the TRBF and retinal blood SO₂ were also studied.

Methods: One eye of 11 young healthy subjects was randomly chosen for the study. TRBF and retinal SO₂ measurements were obtained under conditions of normoxia, hyperoxia and hypoxia. The order of hyperoxia and hypoxia was be randomized between subjects. The measurements were repeated after a week interval. Pulse rate, blood pressure and intraocular pressure were also measured.

Results: The preliminary results shows that as the arterial P_ETO₂ was increased from baseline (P_ETO₂₌100mmHg) to 200 and 300mmHg, the TRBF significantly reduced (reANOVA, P=0.04) from 36.08 μl/min (+4.78) to 33.27 μl/min (+5.06) and 28.23 μl/min (+2.84). Lowering the arterial P_ETO₂, from baseline to 80, 60 and 50mmHg, TRBF significantly increased (reANOVA, p=0.02) from 32.40 μl/min (+3.38) to 35.51 μl/min (+1.76), 41.37 μl/min (+1.04) and 46.18 μl/min (+0.72) with simultaneous reduction in the arterial blood SO₂ content from 96.75 % (+ 0.71) to 94.38% (+ 0.16), 92.06% (+ 1.41), and 88.82% (+ 0.35) respectively. The coefficient of repeatability (COR) of TRBF and retinal arterial blood SO₂ values were 2.13 μl/min and 3.34 % respectively.

Conclusions: As hypothesised, increase in arterial P_ETO₂ from baseline decreases the TRBF. Conversely, decreasing the arterial P_ETO₂ from baseline increases the TRBF with simultaneous reduction in the retinal arterial blood SO₂. Retinal blood flow and oxygen saturation measurements performed under safe levels of hypoxia and hyperoxia were repeatable in healthy adults.