Z HOT TOPIC Z 

Authors: Saba Samet, Esther G. Gonzalez, Graham E. Trope, Luminita Tarita-Nistor
Author Disclosure Block: S. Samet: None. E.G. Gonzalez: None. G.E. Trope: None. L. Tarita-Nistor: None.

Abstract Body:

Purpose: Glaucoma is associated with degeneration not only in the primary visual pathways, but also in the corpus callosum. Binocular rivalry can provide insights into the dynamics of the visual system, including the intra- and inter-hemispheric processing of visual information. In this study we used binocular rivalry to determine whether changes in the visual pathways and corpus callosum can be detected behaviourally in early glaucoma.
Study Design: Prospective, observational study.
Methods: Thirty-one patients with early stage open angle glaucoma (mean age 66 ± 12 years) and 30 age-matched (mean age 63 ± 10 years) controls participated. In both groups, the functional (stereo-acuity, visual field mean deviation, visual acuity) and structural (retinal nerve fiber layer, average cup-to-disc ratio, vertical cup-to-disc ratio) measures were equivalent for the left and right eye of each participant. The two groups were equivalent in functional but not structural measures. Rivalry stimuli were 5 deg diameter discs of 3cpd vertical and horizontal sine wave gratings. They were presented dichoptically centrally, 5 deg peripherally to the left and to the right, in random order. The outcome measure was the rivalry rate (RR), defined as the number of perceptual changes per minute.
Results: RR was analyzed with a 3 (Location: central, right, left) x 2 (Group: glaucoma, control) mixed factorial ANOVA. There was a significant Location main effect F(1.5, 89.8) = 22.5, p < 0.001, partial η2 = 0.28 and an interaction Location x Group effect F(1.5, 89.8) = 3.8, p = 0.04, partial η2 = 0.06. Pairwise comparisons showed that RR with the central stimuli was significantly higher than those with peripheral (right or left) stimuli, p < 0.001. Also, RR of the control group was significantly higher than that of the glaucoma group for the central stimuli (p = 0.03), but not for the peripheral stimuli. The average RR of the control group was 26% higher than that of the glaucoma group for the central stimuli.
Conclusions: Using binocular rivalry, this study detected changes in inter-hemispheric, but not in intra-hemispheric processing of information in patients with early stage glaucoma. These results indicate dysfunction in the inter-hemispheric transfer in early glaucoma that was detected behaviourally before any changes in standard functional measures.