Comparison of ring 1 parameters in 37-segment multifocal electroretinography between onset and offset conditions of ring 2 to 4 in normal subjects

AIM: To investigate whether the response of a central hexagonal element corresponding to the macular area in conventional multifocal electroretinography (mfERG) tests was the same as that of experimental mfERG using single central hexagonal element stimulation. ● METHODS: Prospective, observational study. Thirty healthy subjects were included in this study. mfERG recordings were performed according to two protocols: stimulus with 37 hexagonal elements (protocol 1), and stimulus with a single central element created by deactivating the other 36 hexagonal elements (protocol 2). We compared differences between ring 1 parameters in each protocol. ● RESULTS: In protocol 1, the first positive component (P1) implicit time and P1 amplitude were 37.8±1.8ms and 6.3±2.7 µV. After single element stimulation (protocol 2), double positive waves appeared. The implicit time and amplitude of P1 were 40.7±2.4ms (P<0.001) and 9.1±3.3 μV (P=0.001), respectively. The implicit time and amplitude of the second positive component (P2) were 68.0±4.5ms (P<0.001, compared with P1 in protocol 1) and 12.3±4.7 µV (P<0.001, compared with P1 in protocol 1), respectively. The amplitude of P2 in protocol 2 was about two times higher than that of P1 in protocol 1. ● CONCLUSION: mfERG responses of a central hexagonal element in a single element stimulation protocol are different from those of multiple element stimulation. The positive wave is more enhanced compared to that of the conventional protocol and it elongated into two wavelets.