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Hao F Zhang, Ji Yi, Siyu Chen, wenzhong Liu; Can OCT be accurate in quantifying retinal oxygen metabolism?. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):3306.
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© ARVO (1962-2015); The Authors (2016-present)
To explore whether OCT can be a potential candidate for accurate measurement of retinal oxygen metabolism towards early diagnosis of ischemic retinal diseases.
We first used statistical methods to numerically simulate photon transport in the retina to mimic OCT working under different spectral ranges. Then we analyze accuracy of OCT oximetry subject to parameter variations such as vessel size, pigmentation, and oxygenation. We then developed an experimental OCT system based on the spectral range identified by our simulation work. We applied the newly developed OCT to measure both retinal hemoglobin oxygen saturation (sO2) and retinal retinal flow. To measure blood flow, we performed double-circular-trajectory scans around the optic disk to obtain the absolute blood velocity. After obtaining the retinal sO2 and blood velocity, we further measured retinal vessel diameter and calculated the retinal oxygen metabolism rate (MRO2). To test the capability of our OCT, we imaged wild-type Long-Evans rats ventilated with both normal air and air mixtures with various oxygen concentrations.
Our simulation suggested that OCT working within visible spectral range is able to provide accurate measurement of retinal MRO2 using invers Fourier spectral reconstruction. We refer our newly developed OCT as vis-OCT, and showed that vis-OCT was able to measure the sO2 value in every single major retinal vessel around the optical disk as well as in micro retinal vessels as shown in Figure 1. When breathing normal air, the averaged sO2 in arterial and venous blood in Long-Evans rats was measured to be 95% and 72%, respectively. When we challenge rats using air mixtures with different oxygen concentrations, vis-OCT measurement follows analytical models of retinal oxygen diffusion and pulse oximeter well.
Vis-OCT is a sensitive tool to measure retinal MRO2 with a high repeatability. It opens up a new window to investigate several significant blinding diseases, such as diabetic retinopathy and glaucoma, which strongly associate with retinal oxygen metabolic disorders.
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