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N.V. Rangaswamy, L.J. Frishman, U. Dorotheo, R.A. Tang, J.S. Schiffman; The Photopic ERG in Patients with Optic Neuropathies and Primates with Inner Retinal Blockade . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2143.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To determine the types of optic neuropathies in humans that alter the photopic flash ERG response and to investigate the cellular origins of the waves that are affected using pharmacological agents in primates. Methods: Photopic flash ERGs were recorded differentially between the two eyes from 23 patients diagnosed with optic neuropathy (17– anterior ischemic optic neuropathy (AION) and 6– compressive optic neuropathy (CON)) and from 18 eyes of 13 monkeys (Macaca mulatta) with DTL electrodes. The stimulus consisted of brief (<5 ms) red (λmax = 660 nm) ganzfeld flashes (energies ranging from 0.5 to 2.0 log ph td.s) delivered on a rod–saturating blue background of 3.7 log sc td (λmax = 460 nm). An eye of the patient with ischemic changes at the disc was classified as symptomatic if it showed visual field defects with a mean deviation (MD) of p<2%. Recordings in macaque monkeys were made before and after inner retinal blockade with tetrodotoxin citrate (TTX :1–2 µM; n=7), TTX+NMDA (1–2 µM; n–methyl–D–aspartic acid: 1.4–6.4 mM; n=7) and cis–2,3 piperidine dicarboxylic acid (PDA: 3.3–3.8 mM; n=4). Results: The PhNR amplitude was significantly reduced in symptomatic eyes with AION (p=3.6X10–8), asymptomatic eyes (p=0.036), and CON (p=0.0054) patients compared to controls, the PhNR amplitude in the symptomatic eye showed a moderate correlation with field defects similar to previous findings in open angle glaucoma. The a–wave also was reduced significantly in the symptomatic eye (p=0.0002) of AION patients. The i–wave, a positive wave on the trailing edge of the b–wave peaking around 50 ms, became more prominent in eyes in which the PhNR was reduced. In monkeys, the PhNR was eliminated by TTX. The a–wave at the peak and later times was reduced by TTX, further reduced by NMDA and eliminated after PDA for the red stimuli used in this study. Conclusions: PhNR amplitude is significantly reduced in all optic neuropathies studied to date. This reduction reflects loss of a spike–driven contribution to the photopic ERG. There also are small spike–driven contributions to the a–wave elicited by full field red stimuli. The i–wave, which becomes more prominent when the PhNR is reduced, has origins in the off–pathway distal to the ganglion cells.
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