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Akshay Gurdita, Bingyao Tan, Vivian Choh, Karen M Joos, Kostadinka K Bizheva; Physiological and Morphological Effects of Acute Intraocular Pressure Elevation in Pigmented and Albino Rats. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1992.
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© ARVO (1962-2015); The Authors (2016-present)
To compare the electrophysiological and morphological effects of acute moderately elevated intraocular pressure (IOP) in Sprague Dawley (SD), Long Evans (LE) and Brown Norway (BN) rat retinas.
Eleven-week old male SD (n=5), LE (n=5) and BN (n=5) rats were dark-adapted for at least 12 hours before being anesthetized with isoflurane. Corneas were topically anesthetized and pupils were dilated prior to collection of IOP, and either scotopic threshold responses (STRs), Maxwellian flash electroretinograms (ERGs), or 3D volumetric OCT images of the rat retinas from both eyes before, during and after IOP elevation. The right eye IOP was raised to ~35 mmHg for 1 hour using a vascular loop around the equator of the eye, while the left eye served as a control. The retinal images were acquired with a research-grade ultrahigh resolution optical coherence tomography (UHR-OCT) system (with 3.2 µm axial and ~5 µm lateral resolution). STRs, ERGs and UHR-OCT images were acquired on 3 days separated by one day of no experimental manipulation.
During IOP elevation, peak positive STR responses in LE (mean±sem: 143±17 mV) and BN (cf 125±15 mV) rats have significantly higher responses compared to SD (33±4 mV) rats (p=0.0002 for both). Similarly, during elevated IOP, b-wave amplitudes were 2-fold higher in LE and BN rats compared to SD rats (598±120 mV & 578±112 mV, vs 283±52 mV; p=0.0001 for both). However a-wave amplitudes in BN rats were about 1.2- and 1.9-fold higher than in LE and SD rats (287±62 mV vs 230±49 mV & 154±34 mV; p=0.0152 & p=0.0001, respectively). UHR-OCT images showed backward bowing in all groups during IOP elevation, with a return to typical form 30 minutes after IOP elevation. The inner plexiform layer (IPL) in LE and BN rats were significantly thicker than in SD rats (41.1±0.5 µm & 38.2±0.3 µm vs 34.2±0.4 µm; p=0.0002 & p=0.0314). Compared to pre-loop conditions, IPL thicknesses increased during IOP elevation for all three rat strains (p=0.0018).
Our results suggest that retinal morphology and physiology in different rat strains respond to elevated IOP uniquely.
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