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A. J. Vingrys, C. T. O. Nguyen, J. Charng, B. V. Bui; Repeated IOP Spikes Can Produce Permanent Ganglion Cell Dysfunctions. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2755.
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We consider whether 1. repeated intraocular pressure (IOP) spikes can produce permanent retinal dysfunction and 2. whether the beneficial effect that fish-oil diet has for retinal neurons can modify this loss.
Sprague-Dawley rats (n=41) were subjected to multiple IOP spikes at 7-day intervals. In Expt 1. ten aneasthetised (60:5 mg/kg, ketamine:xylazine) 12-week old animals, raised on normal rat chow, underwent multiple (x3) weekly IOP challenges (anterior chamber cannulation, 60 mmHg for 1 hour) in one eye with the fellow eye acting as control (cannulation, 15 mmHg). In Expt 2. 31-rats were raised on Omega-3 sufficient (N-3+; n=15) or deficient (N-3-; n=16) diets from birth as detailed elsewhere (Nguyen et al, IOVS, 2008) and had weekly IOP challenges (70 mmHg for 1 hour) commenced at 20 weeks of age for 3 repeats. Electroretinogram (ERG, -6.28 to 2.28 log cd.s/sq.m) responses were measured in anaesthetized dark-adapted (>12 hours) animals at baseline (prior to IOP challenge) and a week following each IOP challenge to isolate rod receptoral (PIII), ON-bipolar (PII) and ganglion cell (STR) components.
Repeated IOP spikes produce little effect on photoreceptor (-561±17 vs -559±16; p=0.89) and ON-bipolar cell (1260±30 vs 1220±30; p=0.13) function. In contrast, the ganglion cell pSTR was significantly decreased (12.5±0.8 vs 10.5±1.1; p<0.035) and the nSTR significantly increased (-15.8±0.5 vs -17.1±0.6; p<0.035) after 3 insults. The Omega-3 sufficient diet reduced the magnitude of the loss and delayed its onset. Compared with its own control, the N-3+ group only gave a significant pSTR loss (-22% p<0.035) after the 3rd spike whereas the N-3- group gave a significant 34% loss (p<0.035) after the initial spike that grew in magnitude to reach a 44% loss following the 3rd spike (p<0.035).
Repeated IOP spikes produce little effect on outer and middle retinal function but give permanent loss of ganglion cell function that can be modified by diet. This suggests that chronic IOP challenge is not needed to produce ganglion cell injury.
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