Modelling visual field loss and spatial summation characteristics of patients with glaucoma across the 30-2

Abstract

Purpose : Different sized stimuli have been suggested for examination of the visual field (VF) of patients with glaucoma. Small stimuli (e.g. Goldmann (G) I-II) operating within complete spatial summation (Ac) have been shown to reveal the greatest number and depth of VF defects, but have a narrower dynamic range compared to larger stimuli (e.g. GIII-V). We determined the optimal stimulus sizes to assess VF defects of different depths and to model Ac, which may guide stimulus selection in glaucoma patients.

Methods : 30 patients (mean age: 62 ± 10.7 years) with early to moderate glaucoma (average mean deviation: -3.28 ± 2.24 dB) and a control group of 60 normal, healthy subjects (mean age: 42.5 ± 16.3 years) underwent VF testing on the Humphrey Field Analyzer using GI-V across the 30-2 test grid in full threshold mode. Thresholds were converted into a 50 year-old equivalent subject for analysis. The number of ‘events’ (number of points below the 95% lower limit of normal) and global indices (mean deviation and pattern standard deviation) were determined. Ac values were obtained using segmental nonlinear regression and modelled for glaucoma subjects.

Results : Stimuli operating within Ac (GI, GII) revealed more ‘events’ (31.9 ± 22.2) compared to GIII-V (21.9 ± 18.1, p=0.015). GI-II revealed worse global indices MD and PSD compared to GIII-V (p<0.01). On average, stimuli outside of Ac detected 43.3% of the magnitude of defect found using stimuli within Ac, i.e. underestimation (Figure 1). There was an eccentricity-dependent effect, with central locations showing more underestimation (p<0.0001). Modelled Ac values in glaucoma patients were enlarged by a mean of 0.32 ± 0.24 log degrees², and were correlated with defect depth (R²=0.54, p<0.0001).

Conclusions : Stimuli close to or within Ac reveal the maximum threshold elevation in glaucoma patients. Ac enlarges with greater VF loss; however, defect depth is significant before Ac reaches GIII-V. Different sized stimuli may be useful for different stages of disease severity and at different locations to maximise defect detection and dynamic range.

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

 

Figure 1: Ratio (R) (mean ± 95% confidence interval) of threshold elevation found with stimuli outside Ac divided by the defect found using stimuli within Ac as a function of spatial location (color coded by the inset 30-2 figure). The gray shaded region indicates underestimation by stimuli outside Ac.