Changes in Photopic Negative Response (PhNR) After Vitrectomy

Abstract

Abstract: : Purpose: The photopic negative response (PhNR) is a negative component of photopic ERG appearing after the b–wave, and was suggested to reflect the activity of ganglion cells and their axons. It has been shown that patients with glaucoma or optic nerve diseases have a selective reduction in the PhNR. In this study surgical damage of the retina was estimated by photopic ERG including PhNR. Methods: Photopic ERGs were recorded from 20 eyes of 19 patients with an idiopathic macular hole (IMH) and 14 eyes of 14 patients with an epiretinal membrane (ERM) before and 3 months after vitrectomy. Patients with IMH underwent vitrectomy with inner limiting membrane (ILM) peeling assisted by indocyanine green and fluid gas exchange. Patients with ERM underwent vitrectomy with membrane peeling. Photopic ERGs were elicited by white Ganzfeld flashes (1.91 cd–s /m²) on a rod suppressing blue background (18 cd/m²). The amplitude of the a–, b–wave, and PhNR of the photopic ERGs were analyzed. Goldmann perimetry was also performed before and after surgery. Results: There was no significant difference in the amplitudes of a– and b–waves before and after surgery for both IMH and ERM patients. The amplitude of the PhNR in the IMH group was reduced significantly after surgery (pre–surgery, 31.5±11.8 µV; post–surgery, 22.5±13.9 µV; P = 0.047). The PhNR in the ERM group did not change significantly (pre–surgery, 26.6±11.2 µV, post–surgery, 22.8±13.8 µV; P = 0.33). None of the patients in both groups had a visual field loss after surgery. Conclusions:Subclinical functional damage in the inner retinal layer after vitrectomy was suggested in patients with IMH.

Keywords: electroretinography: clinical • vitreoretinal surgery • ganglion cells