The rate of functional recovery from acute IOP elevation.

PURPOSE: To evaluate the recovery of retinal function after acute IOP elevation.
METHODS: The electroretinogram (ERG) was measured before, during, and after IOP increased to 50 and 70 mm Hg at different durations in anesthetized, dark-adapted rats (n = 5-7). Signals were collected for dim and bright flashes (-4.95 and 1.0 log cd . s/m(2)) and analyzed in terms of the photoreceptoral (P3), postreceptoral (P2), and inner retinal (negative scotopic threshold response [nSTR]) responses. Parameters (treatment/baseline, %) were compared across time by using repeated-measures ANOVA and t-tests. The rate of recovery was quantified with a logistic function and compared by bootstrap.
RESULTS: IOP spikes induce greater loss (P < 0.01) and slower recovery (P < 0.001) in the nSTR compared with the P2 and P3 responses. IOP spikes having common integral (pressure x duration, 2100 mm Hg x minutes) for insult gave significantly greater P2 and nSTR dysfunction at the higher pressure (70 vs. 50 mm Hg, nSTR reduced to -2.5% +/- 0.5% vs. 20.3% +/- 6.5%, P < 0.05). The higher pressure also produced significantly slower nSTR recovery (50% recovery time [t(0.5)] 70 vs. 50 mm Hg: 33.1 vs. 21.7 minutes; P < 0.05). At a given IOP (70 mm Hg), t(0.5) showed a linear relationship with duration (15 vs. 30 vs. 60 minutes' exposure: t(0.5) 16.7 vs. 33.1 vs. 63.2 minutes; P < 0.05) and integral.
CONCLUSIONS: Ganglion cell function recovers slower than the outer retina after IOP insult, with peak IOP being the principle determinant of functional loss and recovery. For a fixed pressure, functional recovery is linearly related to exposure.