Repeatability of pattern electroretinogram measurements using a new paradigm optimized for glaucoma detection

Abstract

Purpose: To determine the within-trial and between-trial repeatability of pattern electroretinogram (PERG) measurements in healthy and patient eyes, using a new clinical instrument, the PERGLA.

Study design: In all, 70 eyes of 35 healthy individuals (intraocular pressure <22 mm Hg, healthy optic disc by stereophotograph assessment, standard visual fields within normal limits) and 90 eyes of 45 clinic patients (ocular hypertensive, glaucomatous optic neuropathy by stereophotograph assessment and/or repeatable abnormal visual fields) enrolled in the University of California, San Diego Diagnostic Innovations in Glaucoma Study (DIGS) were evaluated. Average mean deviation of patient eyes on standard automated perimetry was -1.81 dB (SD=2.61).

Methods: The PERG was recorded using the PERGLA paradigm from both eyes simultaneously twice (ie, 2 trials) by a single operator with electrodes being removed and reattached between recordings. Repeatability of PERG amplitude (microV) and phase (pi rad) between 2 runs within a single trial (within-trial condition) was compared with repeatability between 2 trials (ie, after electrode replacement, between-trial condition) by calculating the coefficients of variability (CVs) and the intraclass correlation coefficients (ICCs) and displaying Bland-Altman plots.

Results: For healthy eyes, amplitude CVs (SD) were 11.5% (11.5) and 9.9% (0.79) for within-trial and between-trial conditions, respectively. ICCs were 0.91 and 0.85. Phase CVs were 1.3% (1.5) (within-trials) and 1.5% (1.4) (between-trials) and ICCs were 0.85 and 0.88. For patient eyes, amplitude CVs (SD) were 12.2% (10.1) and 11.2% (7.5) for within-trial and between-trial conditions, respectively. ICCs were 0.92 and 0.89. Phase CVs were 2.2% (2.2) (within-trials) and 2.4% (2.2) (between-trials) and ICCs were 0.82 and 0.83. Bland-Altman plots indicated good agreement between the repeated recordings and were similar within-trials and between-trials for healthy and patient eyes.

Conclusions: Repeatability of PERGLA recordings is good and is similar within-trials and between-trials for both healthy and patient eyes suggesting this technique is promising for monitoring change over time.

Figure 1

(Top) Bland-Altman plot showing agreement between the differences between the first and second amplitude measurements (i.e., Δ amplitude) for between-trial PERGLA amplitude measurements compared with the average of these two measurements, for healthy eyes. Variability is low and stable across the range of mean amplitudes. (Bottom) Within-trial Bland-Altman plot for healthy eyes. Variability is low and stable across the range of mean amplitudes.

Figure 2

(Top) Bland-Altman plot showing agreement between the differences between the first and second amplitude measurements (i.e., Δ amplitude) for between-trial PERGLA amplitude measurements compared with the average of these two measurements, for patient eyes. A significant (Pearson’s r, p = 0.01) proportional bias is present with amplitude from the first trial tending to be greater than amplitude from the second trial in eyes with larger amplitudes. (Bottom) Within-trial Bland-Altman plot for patient eyes. Visual inspection suggests that as average within-trial amplitude increases agreement decreases, somewhat.