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Wadih M Zein, Antonello Fadda, Brett G Jeffrey, Robert B Hufnagel, Amy Turriff, Ramiro Maldonado, Brian Patrick Brooks, Benedetto Falsini, Paul A Sieving; Cycle-by-Cycle Electroretinography: Utilizing a Widely-Available Instrument to Assess Microvolt Signals in Usher Syndrome. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4278.
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© ARVO (1962-2015); The Authors (2016-present)
1. To investigate the validity of microvolt 30-Hz Flicker responses in patients with Usher syndrome2. To share a protocol for cycle-by-cycle (CxC) Fourier analysis of a steady state signal obtained using a widely-available commercial electroretinography (ERG) console
Photopic ERGs were recorded from both eyes of twenty-one patients with a clinical diagnosis of Usher syndrome, enrolled under National Eye Institute protocol 05-EI-0096 (NCT00106743) or 15-EI-0128 (NCT02471287), between January and October, 2016. Cone flash and 30-Hz flicker responses were obtained according to International Society for Clinical Electrophysiology of Vision (ISCEV) standards using a UTAS console (LKC, Gaithersburg, MD) and bipolar Burian-Allen electrodes (Hansen Ophthalmic Instruments, Iowa City, IA). A steady state 32-Hz flicker signal spanning 15 seconds (based on Sieving PA et al. IOVS 1998) was obtained using an Espion3 console (Diagnosys, Lowell, MA). Software developed for CxC analysis was used to calculate signal-to-noise ratio (SNR) and measurement uncertainty. The best 5 seconds interval was selected for final analysis and a low frequency filter was applied. Right eye data was used for statistical analysis.
Patient age ranged from 16 to 75 years (mean 50, SD 18) and molecular testing was positive for biallelic USH2A mutations in 8 patients, MYO7A in 4, GPR98 in 2, USH1C in one; results were pending or inconclusive in six patients. ISCEV 30-Hz flicker ERG amplitudes ranged from 0.71 to 8 uV (mean 2.81, SD 1.77). Discrete Fourier transform failed to identify a peak at the stimulus frequency for any of these patients indicating these recordings were at noise-level. Statistical analysis of the CxC recordings (based on spread of single cycle Fourier components and also on the SNR threshold) identified 10 patients and three eyes where signal was not different from noise. In the other 19 eyes, the right eye amplitude ranged from 0.57 to 5.68 uV (mean 2.34, SD 1.28) and the SNR from 1.03 to 31.47 (mean 8.44, SD 6.68).
CxC ERG, recorded using a widely-available commercial instrument, is a valuable technique to assess the validity and SNR of microvolt signals common in Usher syndrome. It should be considered for any trials assessing the natural history and potential response to therapeutic intervention.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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