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Jena Tavormina, Ronald M Hansen, Anne Moskowitz, Heidi L Rehm, Margaret Kenna, Anne Fulton; Scotopic and Photopic ERG Responses in Pediatric Patients with Usher Syndrome. Invest. Ophthalmol. Vis. Sci. 2014;55(13):332.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate scotopic and photopic ERG responses in pediatric patients with a genetic diagnosis of Usher Syndrome, a recessively inherited ciliopathy characterized by hearing loss and retinal degeneration affecting both rods and cones.
Twenty-two patients (age 2 months to 23 years) with USH2A (n=13) or MYO7A (n=9) disease were studied. ERG responses to a range of full-field scotopic and photopic stimuli (including the ISCEV standard conditions) were recorded and compared to responses in healthy controls (n=72). A model of the activation of phototransduction was used to estimate rod photoreceptor sensitivity (SROD) and saturated amplitude (RROD). Post-receptor b-wave sensitivity was characterized by the stimulus that produced a half maximum response (log σ) and saturated b-wave amplitude (VMAX). Dark adapted thresholds were estimated using a two-alternative, forced choice method in all patients.
Responses to 30 Hz flickering stimuli were detected in all USH2A patients (median 99, range 7 to 169 μV) and all MYO7A patients (median 10, range 1 to 18 μV). Photopic b-wave amplitude was within the normal range in nine of the 13 USH2A patients and none of the nine MYO7A patients. In the seven MYO7A patients whose photopic b-wave was detectable, the responses were less than 20% of the normal mean. Scotopic b-waves were detectable in all USH2A patients but only six MYO7A patients; only four USH2A patients had normal scotopic b-wave amplitudes. Responses were sufficient for estimation of both photoreceptor and post-receptor response parameters in nine USH2A and only two MYO7A patients. For these 11 patients, deficits in scotopic post-receptor b-wave sensitivity were greater than deficits in rod photoreceptor sensitivity. Median dark adapted threshold in the 22 patients was elevated 0.9 (range 0.13-2.77) log units compared to normal and did not differ between USH2A and MYO7A patients. Threshold elevation was outside the 99% prediction interval for normal for 14 of the 22 patients, whereas ERG log σ values were outside the 99% prediction interval for normal for 21 of 22.
The greater deficit in post-receptor than photoreceptor sensitivity is consistent with a ciliopathy. In this sample, ERG log σ was more often abnormal than the dark adapted threshold. Therefore, the ERG may be a more sensitive detector of retinal dysfunction than the dark adapted threshold in children at risk for Usher Syndrome.
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