The effect of acute intraocular pressure elevation on peripapillary retinal thickness, retinal nerve fiber layer thickness, and retardance.

PURPOSE To determine whether acutely elevated intraocular pressure (IOP) alters peripapillary retinal thickness, retinal nerve fiber layer thickness (RNFLT), or retardance. METHODS Nine adult nonhuman primates were studied while under isoflurane anesthesia. Retinal and RNFLTs were measured by spectral domain optical coherence tomography 30 minutes after IOP was set to 10 mm Hg and 60 minutes after IOP was set to 45 mm Hg. RNFL retardance was measured by scanning laser polarimetry in 10-minute intervals for 30 minutes while IOP was 10 mm Hg, then for 60 minutes while IOP was 45 mm Hg, then for another 30 minutes after IOP was returned to 10 mm Hg. RESULTS RNFLT measured 1120 microm from the ONH center decreased from 118.1 +/- 9.3 microm at an IOP of 10 mm Hg to 116.5 +/- 8.4 microm at 45 mm Hg, or by 1.4% +/- 1.8% (P < 0.0001). There was a significant interaction between IOP and eccentricity (P = 0.0006). Within 800 microm of the ONH center, the RNFL was 4.9% +/- 3.4% thinner 60 minutes after IOP elevation to 45 mm Hg (P < 0.001), but unchanged for larger eccentricities. The same pattern was observed for retinal thickness, with 1.1% +/- 0.8% thinning overall at 45 mm Hg (P < 0.0001), and a significant effect of eccentricity (P < 0.0001) whereby the retina was 4.8% +/- 1.2% thinner (P < 0.001) within 800 microm, but unchanged beyond that. Retardance increased by a maximum of 2.2% +/- 1.1% 60 minutes after IOP was increased to 45 mm Hg (P = 0.0031). CONCLUSIONS The effects of acute IOP elevation on retinal thickness, RNFL thickness and retardance were minor, limited to the immediate ONH surround and unlikely to have meaningful clinical impact.