Abstract
Abstract: :
Purpose: In order to quantify the effects of therapeutic intervention, or to quantify the natural history of a disease, one must have reliable measures that reflect the visual function of local areas. In this study, we compared the inter–visit repeatability of the multifocal ERG (mfERG) and Humphrey visual fields in patients with RP to that of age–similar control subjects. Methods: Eight patients diagnosed with RP (35.4 ± 9.2 years) were chosen to participate based on good central vision (>20/40) and central Goldmann visual fields (V4e) with diameters of 10° or greater. Each subjects was tested on six visits: four weekly visits, followed by visits at three and six months. mfERGs were recorded to an array of 103 scaled hexagons (Sutter and Tran, 1993) and visual field thresholds were measured using a Humphrey Field Analyzer II (Model 750, Humphrey, San Leandro, CA). The locations of the 103 Humphrey test points were modified to fall at the retinal locations corresponding to the middle of the hexagons of the mfERG stimulus array. Results:To avoid the bias introduced by using percent change calculations, we calculated the log of the ratios of the values on successive visits. The means of these retest ratios were used as a measure of progression and the standard deviations were used to quantify reliability. For mfERG amplitude and implicit time, the majority of patients’ average standard deviations fell within the 99% confidence interval of the mean for the control subjects’ standard deviations. For the Humphrey visual field, almost all of the patients’ average standard deviations were greater than those of the control subjects and the reliability decreased with increasing eccentricity. Conclusions: The reliability of the mfERG in patients with RP was equivalent to that of control subjects, whereas the reliability of the patients’ Humphrey thresholds was significantly poorer.
Keywords: retinal degenerations: hereditary • electroretinography: clinical • visual fields