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Brad Fortune, Tiffany E. Choe, Christy Hardin, Juan Reynaud, Grant Cull, Claude F. Burgoyne, Lin Wang; Deformation of the Rodent Optic Nerve Head (ONH) And Peripapillary Structures during and after Acute Intraocular Pressure (IOP) Elevation. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2437.
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To evaluate changes in ONH and peripapillary structures during and after acute IOP elevation in the rodent eye.
Fourteen adult male Brown-Norway rats were studied under anesthesia (ketamine, xylazine, acepromazine 55:5:1 mg/kg IM). Both eyes were imaged by spectral domain optical coherence tomography (SDOCT, Spectralis, Heidelberg Engineering, GmbH) on two baseline occasions several weeks prior to and again 2 and 4-weeks after the acute IOP imaging session. During the acute IOP session, SDOCT imaging was performed 10 min after IOP was manometrically set at 15 mmHg, then 10, 30 and 60 min after IOP had been elevated to 50 mmHg (N=8) and again 10 and 30 min after IOP had been lowered back to 15 mmHg (recovery). In six others, IOP was elevated to either 40 (N=2) or 70 mmHg (N=4). Acute IOP results are reported for a pattern of 49 horizontal B-scans spanning a 20 deg square and follow-up results are reported for peripapillary circular B-scans. Retinal and retinal nerve fiber layer thicknesses (RT, RNFLT) were measured with custom software by manual image segmentation. Friedman and Dunn's tests were used to assess acute and longer-term effects of acute IOP elevation.
Acute IOP elevation to 50 mmHg caused rapid (within seconds) deformation of the ONH and peripapillary structures, including posterior displacement of the ONH surface and outward bowing of peripapillary tissue; RT decreased progressively from 10 to 30 to 60 min by 16%, 18% and 20% within the area of Bruch’s membrane opening (BMO, P<0.0001), by 8%, 9% and 11% within the central 10 deg (excluding the BMO, P<0.0001) but only by 1%, 2% and 2.4% beyond the central 10 deg (P<0.0001). Recovery was progressive and nearly complete by 30 min. Acute IOP elevation to 40 and 70 mmHg produced similar structural changes but 70 mmHg also interfered with retinal blood flow. There were no changes in peripapillary RNFLT or RT (P=0.08 and P=0.16, respectively) measured 2 and 4 weeks after acute elevation to 50 mmHg.
Acute IOP elevation in the rodent eye causes rapid, progressive but reversible posterior deformation and thinning of the ONH and peripapillary tissues, with only minimal retinal thinning beyond 5 deg of the center of the ONH. No permanent changes in peripapillary RT or RNFLT (for up to 1 month of follow-up) were caused by 60 min of IOP elevation to 50 mmHg.
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