Foveal amplitudes of multifocal electroretinograms are larger following full-field electroretinograms

The clinical standards for multifocal electroretinograms (mfERG) call for adaption to normal room lighting before the mfERG begins. They specify that any assessments where bright lights are used, should be done after the mfERG to prevent excess stimulation of retinal cells. However, full-field electroretinograms (FFERG) are performed prior to mfERGs in some clinical settings. It is unclear from the literature whether the FFERG has an impact on the mfERG. This study seeks to examine the effect of the FFERG on the mfERG when performed sequentially.

Thirty young healthy subjects (age 27.1 ± 3.5 years) were included. Patients reported for two visits and were fully dilated at both visits. At visit one, a FFERG was recorded (VERIS 6.2) using our clinical protocol which includes an ISCEV standard flash sequence; each flash condition was repeated 4-6 times. Following the FFERG, an mfERG was recorded using a 4-min m-sequence at near 100% contrast. At visit two, only the mfERG was recorded. A Burian-Allen contact lens electrode filled with celluvisc was used for all recordings. The two mfERGs were compared for foveal, peripheral, and overall implicit time (IT) and amplitudes (amp). Paired t tests were used to evaluate the data. Coefficient of variation and Bland-Altman analysis was also reported for this patient group.

There was a small but statistically significant difference in foveal amplitudes (amp) (p = 0.004) wherein the amp was larger following the FFERG stimuli. The mean difference was 11.1 nV/deg² (100.9 nV vs 89.8 nV). There was no difference in foveal IT (p = 0.66). There was no difference in overall IT or amp when averaging the entire eye (p = 0.44 amp and p = 0.54 IT) or just evaluating the periphery (p = 0.87 amp and p = 0.051 IT). Bland-Altman analysis found a coefficient of repeatability overall was 1.57 ms (IT) and 10.7 nV/deg² (amp).

The difference in foveal amplitude is likely the result of a small long-term cone adaptation, but further studies are needed. While it is statistically significant, the small difference is unlikely to be clinically important. These results should help increase clinical confidence in mfERG results when recorded following a FFERG.