Pattern electroretinogram to detect glaucoma: comparing the PERGLA and the PERG Ratio protocols
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To detect early glaucoma, Porciatti and Ventura suggested in 2004 the pattern electroretinogram (PERG) protocol “PERGLA” with the following features: (1) skin electrodes, (2) steady-state reversal (15 rps) of horizontal 1.6 cpd gratings and (3) Fourier-based analysis. We compared this to our “PERG Ratio” protocol which uses (1) corneal (DTL) electrodes, (2) nearly the same reversal rate, but 2 check sizes of 0.8° and 16° and (3) Fourier-based analysis using the ratio of amplitudes to the 2 check sizes.
We examined 16 eyes with glaucoma (age 64 ± 7 years) and a control group (n = 13, age 59 ± 8 years). Responses to all stimuli were simultaneously recorded with both electrode types using PERGLA-type gratings and checkerboards as necessary for the PERG Ratio.
The median intra-individual test–retest coefficient of variation in normals pooled across stimuli for skin was 10.0 (95 % CI 1–85 %) and for DTL 9.95 (0.5–49 %), and they are thus nearly identical. The amplitudes obtained from skin were on average 30 % of those with DTL; the skin’s signal-to-noise ratio (SNR) was 66 % of DTL electrodes. Glaucoma detection was assessed via receiver operating characteristics (ROCs). Using skin electrodes, ROC area-under-curve (AUC) was 72/76/72 % using gratings (PERGLA), checks or the PERG Ratio, respectively. Using DTL electrodes, the ROC areas were 60/67/77 %; the last value corresponds to the PERG Ratio protocol.
Our results suggest that skin electrodes are a valid alternative to corneal electrodes: their advantages being no direct eye contact and smaller normal amplitude range compared to DTL; disadvantages: amplitude reduced to 30 % of DTL and SNR ratio reduced to 66 % of DTL. Efficacy in detecting glaucoma was a little higher with the PERG Ratio protocol (ROC AUC: 77 %, PERGLA: 72 %), but not significantly so.
KeywordsPattern ERG PERG Glaucoma Methodology Skin electrode DTL electrode
We thank our participants for taking part in this study, and two anonymous reviewers for supportive critique.
Conflict of interest
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