A new wavelet in the multifocal electroretinogram, probably originating from ganglion cells

To report the properties of a newly detected positive wavelet on the descending limb of P1 of the first-order kernel of the human multifocal electroretinogram (mfERG).

Twenty eyes of 20 normal individuals, ages 21 to 29 years (mean, 25.6) and nine eyes of 6 patients with optic neuritis ages 5 to 38 years (mean, 17.3) were studied. mfERGs were recorded with a visual evoked response imaging system with the number of stimulus elements set at 37. The stimulus frequency was changed from 75 to 37, 18, 9.4, 4.7, and 2.3 Hz, and the contrast of the stimuli was lowered to 50%.

In normal eyes, a positive wavelet appeared on the descending limb of P1 of the first-order kernel of the mfERG when the stimulus frequency was reduced from 75 to 18 Hz. The wavelet had a mean amplitude of 4.2 nV/deg(2) and a mean implicit time of 34 ms at 18 Hz. When the stimulus frequency was reduced further to 2.3 Hz, the amplitude of the wavelet increased significantly (P < 0.05) compared with that at 18 Hz. The amplitudes of the wavelet elicited from the nasal side of the retina were significantly larger (P < 0.05) than those from the temporal side and decreased significantly (P < 0.05) with increasing distance from the optic disc. The wavelet was not present in any of the patients with newly diagnosed optic neuritis, but reappeared with recovery from the disease. The recovery of the wavelet correlated significantly with the recovery of visual acuity and of central critical fusion frequency.

The amplitude of the wavelet on the descending limb of P1 of the first-order kernel of the mfERG was dependent on the stimulus frequency and the retinal locus. The wavelet was not present in the mfERGs recorded in patients with optic neuritis, but returned with recovery from the disease. These findings suggest that the neural activity of the ganglion cells give rise to this wavelet.