Effect of repeated IOP challenge on rat retinal function.

PURPOSE To characterize the effect of repeated brief intraocular pressure (IOP) elevations and the effect of IOP fluctuation on retinal function. METHODS The effects of one, two, and four episodes (70 mm Hg, 15 minutes) are compared by defining the time course of functional recovery after insults. The effect of IOP variation is considered by comparing a constant with a varying insult, keeping a common IOP-time integral (one 60-minute vs. two 30-minute vs. four 15-minute insults; 70 mm Hg). IOP elevation is induced by anterior chamber cannulation in anesthetized, dark-adapted rats (n = 5-7 per group). Electroretinograms are recorded every 6 minutes throughout each event. Recovery time course is modeled using a logistic function, and time for 50% recovery is compared by nonparametric bootstrap. RESULTS Electroretinographic recovery becomes progressively slower with more IOP episodes for bipolar cell and ganglion cell response (P < 0.05) but not for photoreceptor response (P > 0.05). With regard to IOP variation, bipolar cell recovery after four 15-minute insults is faster than it is after two 30-minute insults (P < 0.05), which is faster than after one 60-minute insult (P < 0.05). Ganglion cell recovery after varying (four 15-minute and two 30-minute) insults is faster than after a constant (one 60-minute) insult (P < 0.05). This improved recovery with varying IOP challenge is greater for bipolar cell than for ganglion cell responses (P < 0.05). CONCLUSIONS 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.