Abstract:
The multifocal electroretinogram (mfERG) is a useful diagnostic technique to detect and quantify macular disease. Its potential as an outcome measure for clinical trials depends on its ability to yield reproducible results on successive tests. This is particularly relevant for patients with central scotomas, who have two potential sources of unreliability: reduced signal amplitude and unsteady fixation. The purpose of this study was to assess the reproducibility of mfERG results of patients with central scotomas due to Stargardt disease.
Ten patients with Stargardt disease, who were screened for ABCR gene mutations, were included in this study. To date, 8 of them (7 women, 1 man, with ages ranging between 29 and 63 years) have completed the recording protocol. A VERIS 4 system was used to record mfERGs elicited by a stimulus consisting of 61 scaled hexagons. Two recording sessions were conducted 2 to 11 weeks apart; two mfERGs were recorded on the same eye in each session. Reproducibility was assessed using the mean vs. difference method (Bland & Altman) and the intraclass correlation coefficient (ICCC).
The amplitude density of the P1 peak in first order kernel responses is presented here. Responses were grouped in rings for analysis. Ring 1 included the central 7 hexagons (fovea and parafovea), and rings 2 to 4 comprised hexagons with progressive eccentricity (perifovea). The test–retest reproducibility data for session 1 vs. session 2 are summarized in the table. The most relevant value is the standard deviation of the test–retest difference – std dev(diff).
Test–retest reproducibility was good overall, but test–retest differences were not negligible. The repeatability coefficient (2 std dev(diff)s) ranged from 26% of mean amplitude (ring 3) to 48% of mean amplitude (ring 1). Thus, the mfERG shows promise as an outcome measure for clinical trials designed to modify the course of maculopathies, but it will not allow the detection of modest treatment effects. The reproducibility of implicit time values was considerably better.
Keywords: electroretinography: clinical • retinal degenerations: hereditary