Effects of glaucoma on detection and discrimination of image blur

Abstract

Blur is one of the most commonly reported visual symptoms of glaucoma, but it is not directly measured by current clinical tests. We aimed to investigate the effects of glaucoma on detection and discrimination of image blur.

People with glaucoma, separated into two groups with (n=15) or without (n=17) central visual field defects measured by 10-2 perimetry, and an age-similar control group (n=18) participated. First, we measured contrast detection thresholds centrally using a 2-interval forced choice procedure. We then measured blur detection and discrimination thresholds for the same stimuli (reference blurs 0, 1 arcmin respectively) using a 2-alternative forced choice procedure under two contrast conditions; 4x individual detection threshold for the low contrast condition, 95% contrast for the high contrast condition. The stimulus was a horizontal edge bisecting a hard-edged circle of 4.5° diameter. Data were analysed by linear mixed modelling.

Contrast detection thresholds for the glaucoma group with central visual field defects were raised by 0.014 ± 0.004 (mean ± SE, Michelson units) (p=0.002) and by 0.011 ± 0.004 (p=0.03) relative to control and glaucoma without central visual field defect groups respectively. Blur detection and discrimination thresholds were similar between groups, with small elevations in blur detection thresholds in the glaucoma groups not reaching statistical significance (detection p=0.29, discrimination p=0.91). The lower contrast level increased thresholds from the higher contrast level by 1.30 ± 0.10 arcmin (p<0.001) and 1.05 ± 0.096 arcmin (p<0.001) for blur detection and discrimination thresholds respectively.

Early-moderate glaucoma resulted in only minimal elevations of blur detection thresholds that did not reach statistical significance in this study. Despite the prevalence of blur as a visual symptom of glaucoma, psychophysical measurements of blur detection or discrimination may not be good candidates for development as clinical tests for glaucoma