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Effect of Repeated IOP Challenge on Rat Retinal Function.

He Z, Bui BV, Vingrys AJ

Dept. of Optometry & Vision Sciences, The University of Melbourne, Cnr Kepple & Cardigan Street, Melbourne, Victoria, 3010, Australia.

Purpose: To characterize the effect of repeated brief intraocular pressure (IOP) elevations and the effect of IOP fluctuation on retinal function. Methods: The effect of single, two and four episodes (70 mmHg, 15 min) are compared by defining the time course of functional recovery following insults. The effect of IOP variation is considered by comparing a constant with a varying insult, keeping a common IOP-time integral (single-60 vs. two-30 vs. four-15 min insults, 70 mmHg). IOP elevation is induced by anterior chamber cannulation in anesthetized, dark-adapted rats (n = 5-7/group). Electroretinograms (ERG) are recorded every 6 minutes throughout each event. Recovery time course is modeled using a logistic function and time for 50% recovery compared by non-parametric bootstrap. Results: ERG recovery becomes progressively slower with more IOP episodes, for bipolar cell and ganglion cell (p < 0.05), but not photoreceptor response (P > 0.05). In regards to IOP variation, bipolar cell recovery following four-15 min insults is faster than two-30 min insults (p < 0.05), which is faster than a single-60 min insult (p < 0.05). Ganglion cell recovery following the varying (both four-15 min and two-30 min) insult is faster than a constant (single-60 min) insult (p < 0.05). This improved recovery with varying IOP challenge is greater for bipolar cell than ganglion cell responses (p < 0.05). Conclusion: Repeated IOP insults lead to cumulative dysfunction in the inner retina. For the conditions used in this study, IOP variation per se is not detrimental but appears to be beneficial.

Published 10 March 2008 in Invest Ophthalmol Vis Sci.
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