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Jesse Gale, Lee Michael, Anthony Phillip Wells; Electrophysiology in ocular hypertension: finding the signal. Invest. Ophthalmol. Vis. Sci. 2020;61(7):3862.
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© ARVO (1962-2015); The Authors (2016-present)
The pattern electroretinogram (PERG) and photopic negative response (PhNR) are reversible signals of retinal ganglion cell stress in ocular hypertension and glaucoma, but the practical application is challenging because there are many sources of noise that obscure the clinically meaningful signals. We conducted a challenge re-challenge clinical observational study, taking multiple measurements from each participant before and after two cycles of intraocular pressure (IOP) lowering treatment, to isolate the signal associated with changes in IOP.
We recorded from 14 patients with a history of raised IOP and no more than a suspicion of glaucoma, before and after one week of treatment with combination dorzolamide 2% and timolol 0.5% drops twice daily, then stopped treatment for a week and then repeated the cycle of measurements before and after another week of treatment. The primary outcome was the effect of treatment on PERG or PhNR amplitudes, but secondary analyses included controlling for individual differences by comparing changes in signal and IOP, and controlling for intraindividual differences by using ratio of PhNR to b-wave. Regression was used to analyse the effect of optic nerve structure and function on electrophysiology outcomes.
A total of 50 measurements from 14 patients were recorded. Mean IOP was 20.5 mmHg before treatment and 12.5 mmHg after treatment. The mean (standard deviation) PERG and PhNR amplitudes were 2.84 (0.92) mV and 24.4 (9.2) mV before treatment and 2.96 (1.03) mV and 22.6 (8.1) mV after treatment (no differences, and no correlation with IOP). However, the PhNR to b-wave ratio, measured as a change in signal, showed the predicted negative correlation with change in IOP, in some eyes (but not all, see Figure).
Repeat electrophysiology measures in the same participants and the use of ratio values can help to isolate IOP-related signals and offer more meaningful data for patient consultation on whether treatment is reducing ganglion cell stress signals.
This is a 2020 ARVO Annual Meeting abstract.
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