Pattern electroretinogram to detect glaucoma: comparing the PERGLA and the PERG Ratio protocols

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 0.8A degrees and 16A degrees and (3) Fourier-based analysis using the ratio of amplitudes to the 2 check sizes. We examined 16 eyes with glaucoma (age 64 +/- A 7 years) and a control group (n = 13, age 59 +/- A 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.