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Shaohua Pi, Tristan Hormel, Xiang Wei, William Cepurna, Acner Camino, Yukun Guo, David Huang, John C Morrison, Yali Jia; Monitoring Retinal Responses to Acute Intraocular Pressure Elevation in Rats with Visible Light Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2019;60(9):187.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate retinal responses to acute intraocular pressure (IOP) in rats using visible-light optical coherence tomography (vis-OCT).
A 1.7-µm axial resolution, 50 kHz sampling rate, fiber-based vis-OCT system centered at 560 nm was built and used to image the retina of brown Norway rats (17 weeks old). The IOP in rat eyes was regulated from 10 mmHg to 100 mmHg by cannulating the anterior chamber with a height-adjustable balanced salt solution reservoir. At each IOP increment, a volumetric raster scan was acquired for angiography and oxygen saturation (sO2) analysis and three sets of dual-circular scans were acquired for blood flow measurement. OCT angiography was generated with SSADA and projected within specific slabs to visualize the en face images of the SVP (Fig. 1A), ICP (Fig. 1B) and DCP (Fig. 1C). The oxygen saturation (sO2, Fig.1D) was measured in retinal major vessels by spectroscopically fitting. Blood flow was measured by the vessel velocity from Doppler phase shift, as well as the vessel Doppler angle and vessel cross-sectional area. Retinal oxygen metabolism was deduced from the difference of oxygen content supplied by arteries and carried away by veins per unit time, and calculated from the sO2 and total retina blood flow.
One eye of each rat was randomly selected and seven eyes were imaged. Vascular perfusion in the three retinal plexuses maintained well until IOP exceeded 70 mmHg (Fig. 1A-C, Fig. 2A). However, a significant drop of the total retinal blood flow (Fig. 2B) was observed earlier than that, with arterial flow reversal confirmed at IOPs of 70 and 80 mmHg (Fig. 2B). In the meantime, the venous sO2 was found to drop gradually as IOP increased (Fig. 1D, Fig 2C), which implies an increased arterial-venous oxygen extraction with steady arterial sO2. The balanced responses of blood flow and oxygen saturation extraction ensured a steady measured retinal oxygen metabolism rate before becoming unattainable at high IOPs. (Fig. 2D). All measured metrics returned to baseline when the IOP was returned to 10 mmHg, indicating a good recovery following acute IOP elevation.
Comprehensive retinal responses to acute IOP elevation, including structure, angiography, blood flow, oxygen saturation and oxygen metabolism can be noninvasively and simultaneously assessed with vis-OCT.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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