Comparison of Electrophysiological and Structural Optic Nerve Head Changes in Ocular Hypertension and Primary Open Angle Glaucoma

Abstract

Abstract: : Purpose: To investigate the relationship between electrophysiological measures of visual function and optic nerve head morphology in Ocular Hypertension (OHT) and early Primary Open Angle Glaucoma (POAG). Methods: 23 early POAG patients (mean age 61.91, SD 9.70 years; SITA MD –2.39dB), 13 untreated OHT patients (mean age 56.54, SD 8.81 years; MD –0.36dB) and 22 controls (mean age 59.41, SD 9.35 years; MD 0.23dB) were recruited following expert grading of digital simultaneous optic disc images. Central Pattern ERGs were recorded by the ISCEV Standard protocol using DTL electrodes. After pupil dilation, a mini ganzfeld elicited flash L&M-cone ERGs with a 650nm pulse of 5ms and 200ms at 1.8Hz on a 450nm background and S-cone ERGs using substitution of 300ms photometrically balanced 450nm and 535nm pulses at 1.67Hz on a 650nm background. ONH morphology was assessed by a series of three 3.4mm diameter OCT scans and three 10⁰ HRT images. Results: Compared to controls both POAG and OHT groups showed significant attenuation of the PERG P50-N95, 5ms and 200ms L&M PhNR with significant differences in HRT parameters for NNR area, cup to disc area ratio (CDAR), cup shape measure and OCT global RNFL thickness (GRNFLT). The S-cone PhNR was significantly reduced in the POAG group but not the OHT group. In the POAG group the most significant correlations (p<0.001) were between the PERG P50-N95 and the NNR:disc area ratio (r:0.415, p:0.005), CDAR (r:-0.532, p:0.0002), CSM (r:-0.518, 0.0003) and GRNFLT (r:0.397, p:0.007) and between the 5ms L&M PhNR and CDAR (r:-0.389, p:0.009). No significant correlations were found in the OHT group. Conclusions: The modest correlation between structural and electrophysiological measures in POAG suggests these techniques identify different aspects of the pathological process. Our data suggest that reduction in measures of visual function may precede changes in ONH morphology in eyes with ocular hypertension.  

Keywords: electroretinography: clinical • optic disc • electrophysiology: clinical