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T.M. Nork, C.B. Y. Kim, M.J. Lucarelli, L.A. Levin, P.L. Kaufman, J.N. Ver Hoeve; Multifocal Electroretinographic (mfERG) Evidence for Persistent Outer Retinal Injury in Chronic Ocular Hypertension in Non–Human Primates . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4663.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To test a hypothesis that outer retinal injury is a persistent feature of chronic experimental ocular hypertension (OHT). Methods: OHT was produced in 8 monkeys (4 rhesus and 4 cynomolgus) by laser scarification of the trabecular meshwork. Two of the animals had had a previous surgical optic nerve transection (ONT, 1 rhesus and 1 cynomolgus) in the treated eye. mfERG testing was performed using VERIS ScienceTM 4.9 for stimulus generation. 103 equal–sized hexagonal elements, which subtended a total of 88o of the visual field, were displayed on a 21" monochromatic stimulus monitor. A binary m–sequence (214–1) with 13.33–ms base period was used. Mean luminance of the stimulus display was 100 cd/m2. ERG–JetTM contact lens electrodes were used. The waveforms were digitally filtered into low [<80 Hz, evoked potential (EP)] and high [>80 Hz, oscillatory potential (OP)] frequency components. The root–mean–square (RMS) of the 9–35 ms (N1–P1) portion of the K1 waveform was averaged in 4 rings radiating from the foveal element. The animals had from 0 to 8 baseline tests prior to OHT. Following OHT, the animals were periodically tested with mfERGs for up to 4.4 years. Results: All of the animals (including the 2 animals with a prior ONT) showed mild to markedly supranormal K1 N1–P1 EP amplitudes (more so for the rhesus than the cynomolgus monkeys). The average RMS values were as much as 1.6 times as great for the OHT eyes as for the fellow eyes. The supranormality showed no tendency to degrade with time as long as the intraocular pressure remained elevated. In some of the animals, supranormal OPs were noted as well. No consistent retinotopic distribution was found. Conclusions: Supranormality is probably an indication of neuronal injury. Its presence in both the ONT as well as intact eyes with OHT means that its origin is the outer retina (e.g., photoreceptors and/or bipolar cells). Persistence of the supranormal response for years suggests either that there is permanent retinal damage (such as death of inhibitory cells) or that the outer retina is in a chronic (and potentially reversible) state of pressure–related ischemia.
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