Time and frequency analysis of simultaneously recorded corneal and non-corneal electroretinogram.

Electroretinograms (ERGs) were simultaneously recorded with corneal and non-corneal (lower or upper eye lid) electrodes in four healthy subjects. 64 traces of the non-corneal ERG were averaged. The two signals were compared in both time and frequency domains. The power spectrum of both signals was computed by the fast Fourier (FFT) and linear prediction (LP) algorithms. Except for amplitude differences, the two signals had almost identical time domain (a- and b-wave latencies) and frequency domain (dominant power spectrum peaks) parameters. It is concluded that non-corneal ERG does not differ significantly from corneal ERG, and that its clinical interpretation can be based on existing corneal ERG data.