Intraocular Pressure Lowering Is Associated with an Increase in the Photopic Negative Response (PhNR) Amplitude in Glaucoma and Ocular Hypertensive Eyes

Abstract

PURPOSE. The aim of our study was to determine whether IOP lowering in glaucomatous and ocular hypertensive (OHT) eyes leads to an improvement in the full-field photopic negative response (PhNR) of the electroretinogram. METHODS.A prospective nonrandomized interventional cohort study was conducted. Patients with OHT or glaucomatous optic neuropathy were recruited, and photopic full-field electroretinograms (ERG) were performed at baseline and then repeated 1 to 2 months later. The change in PhNR amplitude was compared between those eyes that had a significant lowering in IOP (defined as >25% decrease from baseline or to a predetermined target IOP) during follow-up and those that did not. RESULTS.From a cohort of 30 eyes, 18 eyes had a significant reduction in IOP during follow-up (n ¼ 18) and 12 eyes had no significant change in IOP (<25% reduction in IOP, n ¼ 12). A significant increase in PhNR amplitude and the PhNR/b-wave amplitude ratios was observed in the reduced IOP group, but not in the IOP stable group for the two flash intensities used (2.25 and 3.00 cd.s/m 2 ).CONCLUSIONS. The full-field PhNR amplitude provides a potentially reversible measure of inner retinal function that improves after IOP lowering. Further study now is required to assess its use as a measure of optic nerve health in glaucoma patients.(Invest Ophthalmol Vis Sci.

Alpha7 nicotinic acetylcholine receptor agonist promotes retinal ganglion cell function via modulating GABAergic presynaptic activity in a chronic glaucomatous model

“…For this purpose, we analyzed the photopic negative response (PhNR), a sensitive marker of inner retinal function that is damaged in glaucoma patients 39, 40 . The amplitude of the PhNR is proportional to the number of functional RGCs 39–43 .…”

Electroretinography in glaucoma diagnosis

“…Since that time, several other studies have been published on the PhNR that are relevant to glaucoma and considered here. First is the careful study by Niyadurupola and collegues [38], which provides a compelling demonstration of improvement in the PhNR amplitude within 1–2 months of IOP lowering by standard clinical therapy. The eyes that did not achieve significant IOP reduction (<25% reduction) did not have any change in PhNR amplitude over the same period.…”

“…The eyes that did not achieve significant IOP reduction (<25% reduction) did not have any change in PhNR amplitude over the same period. In the group of eyes that did achieve significant IOP reduction (>25% reduction), the improvement in PhNR amplitude was related to the degree of IOP lowering [38]. The authors discussed how this might be a reflection of improved RGC function and/or due to a change in spatial buffering of potassium ion by retinal and optic nerve head glia.…”

Comparing three different modes of electroretinography in experimental glaucoma: diagnostic performance and correlation to structure

“…The utility of the PhNR for assessment of retinal ganglion cell function in glaucoma was first described by Viswanathan and colleagues [36,42] and has since been confirmed by numerous other investigators in clinical studies, particularly when normalized to B-wave amplitude [59,39,60,22,24,61–64] as well as in laboratory studies of both rodent [65,66] and NHP optic nerve injury models [28]. It is possible that limiting the stimulus to localized areas of the macula [67–69,62,23] and/or to a narrower spectral range (with a goal of stronger chromatic contrast) [43] might offer greater improvement of diagnostic performance of the PhNR as compared to the conditions used in this study.…”