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Measuring oxygen saturation in retinal and choroidal circulations in rats using visible light optical coherence tomography angiography.

ABSTRACT: Visible light optical coherence tomography (vis-OCT) has demonstrated its capability of measuring vascular oxygen saturation (sO2) in vivo. Enhanced by OCT angiography, the signal from microvasculature can be further isolated and directly used for sO2 extraction. In this work, we extended the theoretical formulation for OCT angiography-based oximetry by incorporating the contribution from motion contrast enhancement. We presented a new method to eliminate the associated confounding variables due to blood flow. First, we performed in vitro experiments to verify our theory, showing a stable spectral derivative within the selected wavelength bands for sO2 extraction. Then, we tested our method in vivo to measure retinal sO2 in rats inhaling different gas mixtures: normal air, 5% CO2, pure O2, and 10% O2. Absolute sO2 values in major arterioles and venules in the retinal circulation can be accurately measured. In addition, we demonstrated the relative changes of sO2 can be measured non-invasively from choriocapillaris immediately underneath the retinal pigmented epithelium (RPE) in rodents.

SUBMITTER: Chen S

PROVIDER: S-EPMC4541512 | biostudies-other | 2015 Aug

REPOSITORIES: biostudies-other

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Project description:PURPOSE:To report 3 cases of neurofibromatosis type 1 (NF1) with choroidal nodules associated with retinal microvascular changes imaged with optical coherence tomography angiography (OCTA). METHODS:Small case series in 3 NF1 patients. OCTA examinations were performed by a trained examiner (J.J.) after pupillary dilation. A standard scan, centered over the macula measuring 6 × 6 mm and 3 × 3 mm was obtained according to the findings on standard color photography. Additional scans were obtained in the zones with microvascular abnormalities. The segmentation provided by the machine software was used. RESULTS:Corkscrew retinal vessels were observed in association with "placoid"-type choroidal nodules as shown by near-infrared reflectance imaging. In all cases, multiple lesions were found. They were second- or third-order tortuous vessels originating from the superior or inferior temporal veins. OCTA demonstrated that the tortuous venules were located in the superficial capillary plexus, and no abnormalities were found in the deep capillary plexus. DISCUSSION:Corkscrew retinal vessels are part of a spectrum of retinal microvascular alterations seen in association, sometimes overlying choroidal nodules in patients with NF1 and are visualized in the superficial capillary plexus on OCTA. We demonstrated with OCTA that they are not associated with flow loss or ischemia in the superficial and deep capillary plexus. The link between the underlying nodule remains unclear. Since neovascularization was described in choroidal ganglioneuroma, we hypothesize that corresponding secretory substances from Schwann cells, ganglion cells, or melanocytes in choroidal nodules might alter the retinal vasculature. CONCLUSION:We report on 3 cases of NF1 with choroidal nodules in association with retinal microvascular changes imaged with OCTA. OCTA demonstrated preservation of the blood flow in the deep and superficial capillary plexus of the retina. We hypothesize that angiogenic factors secreted by the underlying choroidal nodules could have an effect on the retinal vasculature. Further immunohistological studies in NF1 patients with choroidal nodules to detect angiogenic factors (such as VEGF) are necessary to confirm this hypothesis.

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Measuring oxygen saturation in retinal and choroidal circulations in rats using visible light optical coherence tomography angiography.

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