Variability of the multifocal electroretinogram based on the type and position of the electrode

To evaluate and compare the wave amplitude of multifocal electroretinogram (mfERG) measurements and discomfort from Dawson-Trick-Litzkow (DTL) electrode located on the cornea (cDTL) and on the conjunctival fornix (fDTL) and ERG-jet contact lens electrode (CL).

Thirty-six patients and 18 healthy volunteers were evaluated with three different methods (cDTL, fDTL and CL). Wave amplitude, number of artifacts, number of electrode dislocations and level of discomfort obtained with each electrode were compared. These variables were also compared between patients and healthy volunteers (control group). Comparisons between wave amplitudes were made using intraclass correlation coefficient (ICC).

Responses by the three tested electrode were better correlated (ICC) in patient (0.616-0.756) than in control groups (0.342-0.679). CL provided the highest wave amplitude in both groups (p < 0.005), but it was associated with higher discomfort (p < 0.001) and the highest rate of dislocations (72 and 100 % in control and patients, respectively). Looking at the differences obtained by each electrode between both groups, CL seems to be able to differentiate patient from control in the ring 1 of the mfERG. By contrast, fDTL gave the lowest wave amplitude in both groups, but it had the advantage to, apparently, discriminate between patients and control group in rings 1 and 2. cDTL produced more artifacts than the other electrodes in both groups (p < 0.001).

Although wave amplitude measurements with different electrodes were correlated, they cannot be directly compared, so it is mandatory to create an appropriate normative database with each electrode. Despite providing the lowest amplitudes, fDTL seems to offer the best features to perform mfERG regarding discomfort, number of artifacts and diagnostic capability.