A SubmicroVolt Focal ERG Technique for Evaluating Macular Function in Stargardt/FF Dystrophy: Clinical Assessment of Test Reliability

Abstract

Purpose: : To assess the reliability in a clinical setting of a submicroVolt focal ERG (fERG) technique for evaluating macular function in Stargardt/FF (STDG/FF) dystrophy patients

Methods: : Twenty-six ABCA4- genotyped STDG/FF patients (14/12 M/F, age: 9-32 years; Snellen acuity 0.3-0.8, stable central fixation) and 26 age-matched control subjects were included in the study. fERGs were recorded from the macular region (18 deg) in response to a 41 Hz sinusoidally flickering uniform field on a light adapting background. Sixteen block averages (of 200 events each) were obtained for each eye and recording session (2 to 4 in separate occasions). fERG fundamental component was analyzed for each block to derive amplitude, phase and vector standard error (SE). Noise at the fundamental was estimated on signals averaged asynchronously at 1.1 times stimulus temporal frequency. Intra-test reliability was determined by taking into account either S/N ratio or vector SE

Results: : Although average fERG reliability was lower (p < 0.01) in STDG/FF patients compared to controls, most patients’ responses differed significantly (p < 0.05) from noise. Lowest cut-off reliability, corresponding to a S/N ratio=3, was found in 2 out of 26 patients (7.7%). Test-retest amplitude variability was 0.12 logmicroV in both STGD/FF patients and controls

Conclusions: : The present fERG protocol in STDG/FF provided a reliable macular function test with potential application for monitoring disease progression and treatment

Keywords: retinal degenerations: hereditary • electroretinography: clinical • clinical (human) or epidemiologic studies: biostatistics/epidemiology methodology