Origin of Photopic Oscillatory Potentials Elicited by Long Duration Stimuli

Abstract

Purpose: : It has been reported that the photopic oscillatory potentials (pOPs) on the ascending slope of the photopic b-wave become larger when long duration stimuli are used to elicit the ERG. However, the usual clinical pOPs are filtered from the b-wave without the low frequency components. Earlier studies suggested that the pOPs originated mainly from the activity of amacrine cells (ACs) but also had some contributions from the activity of the ganglion cells (GCs) and the non-identified neural cell on the OFF pathway. The purpose of this study was to investigate the pOPs elicited by longer stimuli to determine the contributions of the GC and OFF pathway to the pOPs.

Methods: : Five normal controls, 10 patients with unilateral glaucoma, and five patients with simple diabetic retinopathy (SDR) were studied. ERGs were elicited by white on white (W/W) stimuli using a contact lens electrode with built-in LEDs. The stimulus durations were 3, 10, 16, and 30 ms that were controlled by the WLS20 (Mayo Co. Japan) system. We compared the photopic negative response (PhNR: GC component) and the i-wave (off component) recorded simultaneously with the pOPs.

Results: : The pOPs were not large with the 3 and 10 ms stimuli, but the pOPs were large with the 16 or 30 ms duration stimuli. The largest pOP was elicited by the 16 ms stimuli and overlapped the b-wave. Although six pOPs were recorded with the 30 ms stimuli, pOP₁ was affected by the photopic a-wave, and pOP₆ was not recorded in two out of five normal eyes. With the 30 ms duration stimuli in the controls, the amplitude of the pOP₂ was 31 µV with a latency of 27 ms, that for pOP₃ was 22 µV with a latency of 36 ms, that for pOP₄ was 12 µV and 43 ms, and for pOP₅ 7 µV and 52 ms. In the eyes with retinal diseases, the amplitudes of pOP₂ and pOP₃ were reduced in eyes with glaucoma, but the reduction was not statistically significant. In the eyes with SDR, both pOP₂ and pOP₃ were significantly reduced. These changes in the pOPs were similar to the changes in the PhNR but different from that of the i-wave.

Conclusions: : These results suggest that the pOPs elicited by longer stimuli originate mainly from the ACs. However, part of the origin of the pOPs is the GC. The pOPs are easy to record with the PhNR and the i-wave in this system. The pOPs can be another component of the photopic ERG which can be used to assess retinal function.

Keywords: electroretinography: clinical • diabetic retinopathy • ganglion cells