The Effect of Acutely Elevated Intraocular Pressure on the Functional and Blood Flow Responses of the Rat Retina to Flicker Stimulation.

Abstract

To evaluate the effect of acutely elevated intraocular pressure (IOP) on the functional and blood flow responses of the rat retina to flicker stimulation. Brown Norway (n = 15) rats were dark-adapted before ketamine/xylazine anesthesia. IOP was raised acutely in one eye to ∼45 mm Hg with a vascular loop. In 11 rats, white light flicker stimulus (10 Hz, 2 seconds duration, 0.80 log scotopic cd·s/m2) was applied before and during IOP elevation, and 10 minutes after loop removal. Changes in the total retinal blood flow (TRBF) and retinal function induced by the visual stimulus were measured simultaneously with a combined optical coherence tomography (OCT) + electroretinography (ERG) system. Systemic blood pressure was measured in the remaining four rats frequently from 10 to 90 minutes post anesthesia injection. The systemic blood pressure remained at 99 ± 4 mm Hg throughout the measurements (n = 4). Under normal IOP, the TRBF was 5.6 ± 1.9 μL/min, and the average retinal blood vessel size (BVS) in the vicinity of the optic nerve head (ONH) was 44.1 ± 4.5 μm. During IOP elevation, the TRBF was significantly lower (3.8 ± 1.2 μL/min, P < 0.01) and the BVS was significantly smaller (35.1 ± 2.6 μm, P < 0.01). Both TRBF and BVS returned to baseline within ∼10 minutes from removal of the vascular loop. The flicker-induced TRBF change measured under normal IOP (6.0 ± 3.3%) was reduced significantly to 0.1 ± 0.3% (P < 0.01) during IOP elevation, and recovered to 5.9 ± 1.7% within 10 minutes after loop removal. During IOP elevation, the magnitude of the ERG second harmonic component (SHC) decreased to 55% of its baseline value (P < 0.01) and remained significantly smaller than baseline (P < 0.01). Acute IOP elevation to 45 mm Hg caused suppression of the retinal functional and TRBF response to flicker stimulation.