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Bingyao Tan, Akshay Gurdita, Kirsten Carter, Camilo Correa Ochoa, Vivian Choh, Karen M Joos, Kostadinka K Bizheva; . Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1981.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the chronic morphological and physiological effects of intermittent intraocular pressure (IOP) elevation in rats.
Eleven-week old male Sprague-Dawley (n=6) rats were dark-adapted for at least 12 hours before isoflurane anesthesia. The IOP in the right eye was raised to ~35 mmHg for 1 hour using a vascular loop around the equator of the eye, on 6 days of the week for a period of 8 weeks. The left eye was left untouched and served as control. Corneas were anesthetized and pupils were dilated prior to collection of either scotopic threshold responses (STRs), flash electroretinograms (ERGs), or 3D volumetric images of the rat retinas from both eyes before, during and after IOP elevation. The retinal images were acquired with a research-grade ultrahigh resolution optical coherence tomography (UHR-OCT) system (3µm axial and ~5µm lateral resolution) at baseline and every 4 weeks. STRs, ERGs and UHR-OCT images were acquired on 3 days separated by one day of no experimental manipulation, respectively.
A- and B-wave amplitudes were highest at week 1 and decreased by weeks 4 and 8 (a-wave: p=0.0365 & p=0.0327, b-wave: p=0.0209 & p=0.0139, respectively) of the study. The STR amplitudes did not change over the course of the study (p=0.4458). The inner plexiform layer (IPL) was thickest at week 1 and decreased by weeks 4 and 8 (p=0.0048 & p=0.0042). The volumetric UHR-OCT images showed backward bowing of the retina at the optic nerve head (ONH) during IOP elevation (p=0.0252), however the extent of ONH depression did not change from weeks 1 to 8 of the study (p=0.3106). The absence of effects over the course of the study are likely a result of low power; the measured power for the STR amplitudes was at 0.20, while that for the ONH depression was at 0.33.
Results from this study suggest that intermittently elevating IOP to moderate levels for an extended period of time can alter the normal morphology and physiology of the retina. More experiments are needed to fully describe all the changes that can occur with our model of IOP elevation.
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