Structure-function relationship in glaucoma assessed with the multifocal Photopic Negative Response (mfPhNR)

Abstract

Purpose : To study the relationship between mfPhNR and retinal nerve fiber layer (RNFL) thickness and visual field sensitivity (VFS) in glaucoma patients.

Methods : mfPhNRs were recorded with an Espion system (Diagnosys LLC) from 16 open angle glaucoma patients and 17 age-matched controls using a custom stimulus (Diagnosys LLC) consisting of six test locations based on maps of visual field test locations to optic disc regions[1-3]. The multifocal stimulus consisted of a 13 ms red (200cd/m²) flash followed by at least 267 ms of blank frames for each region on a constant blue background (35 cd/m²). RNFL thickness corresponding to the mfPhNR test locations was obtained from SDOCT peripapillary circular scans (Heidelberg Inc.). VFS was measured with the SITA standard 24-2 test pattern of the Humphrey Visual Field Analyzer (Carl Zeiss Meditec, Inc.). The correlation of mfPhNR amplitude normalized to the b-wave (NmfPhNR) and RNFL thickness was evaluated by linear regression. The correlation of VFS loss in dB to NmfPhNR amplitude and RNFL thickness was evaluated with a simple linear model. [3]

Results : NmfPhNR amplitudes of glaucoma patients were significantly reduced (p<0.0074) in all but one region. Overall, the NmfPhNR amplitude showed a low but significant correlation with RNFL thickness (r²=0.11, p<0.0001) and VFS loss (r²=0.08, p<0.0001) with r² of individual locations in the range of 0.09 – 0.64 (RNFL) and 0.04 - 0.2 (VFS). NmfPhNR changes were significantly reduced in some test locations before significant RNFL thinning or VF loss. NmfPhNR changes were also found to be normal in other regions with significant RNFL thinning and/or VF loss. RNFL thickness showed better correlation with VFS loss (r²=0.3, p<0.0001) with r² of individual locations in the range of 0.21– 0.61. The magnitude of the change in NmfPhNR amplitude was similar for the superior and inferior macula.

Conclusions : The correlation between mfPhNR and RNFL thickness and VF sensitivity in glaucomatous eyes was quite modest at best. Discrepancies between changes in mfPhNR amplitude and RNFL thickness and/or VF loss may reflect altered mfPhNR generators like glia in the retinal locations early in glaucoma, and the wide range of amplitudes and response variability of control subjects. 1. Garway-Heath et al., Ophthal (2000); 2. Hood, Raza, de Moraes et al. PRER (2013); 3. Hood & Kardon PRER (2009)

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.