Atypical responses to faces during binocular rivalry in early glaucoma.

Purpose: Glaucoma is a progressive optic neuropathy that damages retinal ganglion cells and a neurodegenerative disease as it affects neural structures throughout the brain. In this study, we examined binocular rivalry responses in patients with early glaucoma in order to probe the function of stimulus-specific cortical areas involved in face perception. Methods: Participants included 14 individuals (10 females, mean age 65 ± 7 years) with early pre-perimetric glaucoma and 14 age-matched healthy controls (7 females, mean age 59 ± 11 years). The 2 groups were equivalent in visual acuity and stereo-acuity. Three binocular rivalry stimulus pairs were used: (1) real face/house, (2) synthetic face/noise patch, and (3) synthetic face/spiral. For each stimulus pair, the images were matched in size and contrast level; they were viewed dichotically, and presented centrally and eccentrically at 3 degrees in the right (RH) and in the left hemifield (LH), respectively. The outcome measures were rivalry rate (i.e., perceptual switches/min) and time of exclusive dominance of each stimulus. Results: For the face/house stimulus pair, rivalry rate of the glaucoma group (11 ± 6 switches/min) was significantly lower than that of the control group (15 ± 5 switches/min), but only in the LH location. The face dominated longer than the house in the LH for both groups. Likewise, for the synthetic face/noise patch stimulus pair, rivalry rate of the glaucoma group (11 ± 6 switches/min) was lower than that of the control group (16 ± 7 switches/min) in the LH, but the difference failed to reach significance. Interestingly, the mixed percept dominated less in glaucoma than in the control group. For the synthetic face/spiral stimulus pair, the glaucoma group had lower rivalry rate at all 3 stimulus locations. Conclusion: This study reveals atypical responses to faces during binocular rivalry in patients with early glaucoma. The results may be suggestive of early neurodegeneration affecting stimulus-specific neural structures involved in face processing starting in the pre-perimetric phase of the disease.

Binocular Summation of Visual Acuity at High and Low Contrast in Early Glaucoma.

PRCIS: This study examined the integrity of binocular summation function in patients with mild glaucoma. We found that binocular summation of visual acuity is preserved in these patients, despite their reduced monocular inputs. PURPOSE: Binocular summation represents superiority of binocular to monocular performance. In this study we examined the integrity of binocular summation function in patients with early glaucoma who had structural glaucomatous changes but otherwise had no significant interocular acuity asymmetry or other functional deficit detected with standard clinical measures. MATERIALS AND METHODS: Participants included 48 patients with early glaucoma according to Hodapp, Anderson, and Parrish 2 (HAP2) criteria (age 65±12 y) and 42 healthy controls (age 60±12 y), matched for stereoacuity. Visual acuity was assessed binocularly and monocularly at high (95%) and low (25%) contrast using the Early Treatment Diabetic Retinopathy Study (ETDRS) charts at 6 m. Binocular acuity summation was evaluated utilizing a binocular ratio (BR). RESULTS: Overall, binocular and monocular visual acuity of the control group was better than that of the glaucoma group for both contrast levels, P =0.001. For the glaucoma group, there was a significant difference between BRs at high and low contrast, 0.01±0.05 and 0.04±0.06 ( P =0.003), respectively. For the control group, the difference between BR at high and low contrast was not statistically significant, 0.00±0.07 and 0.02±0.06 ( P =0.25), respectively. CONCLUSION: For patients with early glaucoma, binocular summation function for visual acuity was preserved at both contrast levels. This suggests an adaptation of the visual system in early stages of glaucoma that allows for normal binocular summation in the presence of reduced monocular visual input.

Perceptual Grouping During Binocular Rivalry in Mild Glaucoma.

Purpose: This study tested perceptual grouping during binocular rivalry to probe the strength of neural connectivity of the visual cortex involved in early visual processing in patients with mild glaucoma. Methods: Seventeen patients with mild glaucoma with no significant visual field defects and 14 healthy controls participated. Rivalry stimuli were 1.8°-diameter discs, containing horizontal or vertical sine-wave gratings, viewed dichoptically. To test the grouping, two spatially separated identical stimuli were presented eccentrically to the same or different eyes and to the same or different hemifields. The outcome measures were the time of exclusive dominance of the grouped percept (i.e., percept with synchronized orientations), the rivalry rate, and the epochs of exclusive dominance. Results: For both groups, the grouping occurred primarily for the matching orientations in the same eye/same hemifield (MO SE/SH) and for the matching orientations in the same eye/different hemifield (MO SE/DH) conditions. Time dominance of the grouped percept of the glaucoma group was similar to that of the control group in all conditions. The rivalry rates in the MO SE/SH and MO SE/DH conditions were significantly larger in the control group than in the glaucoma group. The epochs of exclusive dominance of the grouped percept in the MO SE/SH condition were a median of 48-ms longer for the control group, but a median of 116-ms shorter for the glaucoma group when compared to those in the MO SE/DH condition. Conclusion: Patients with mild glaucoma show clear impairments in binocular rivalry while evidence for deficits in perceptual grouping could be inferred only indirectly. If these deficits truly exist, they may have implications for higher levels of visual processing, such as object recognition and scene segmentation, but these predictions remain to be tested in future studies.

Binocular visual function and fixational control in patients with macular disease: A review.

For normally sighted observers, the centre of the macula-the fovea-provides the sharpest vision and serves as the reference point for the oculomotor system. Typically, healthy observers have precise oculomotor control and binocular visual performance that is superior to monocular performance. These functions are disturbed in patients with macular disease who lose foveal vision. An adaptation to central vision loss is the development of a preferred retinal locus (PRL) in the functional eccentric retina, which is determined with a fixation task during monocular viewing. Macular disease often affects the two eyes unequally, but its impact on binocular function and fixational control is poorly understood. Given that patients' natural viewing condition is binocular, the aim of this article was to review current research on binocular visual function and fixational oculomotor control in macular disease. Our findings reveal that there is no overall binocular gain across a range of visual functions, although clear evidence exists for subgroups of patients who exhibit binocular summation or binocular inhibition, depending on the clinical characteristics of their two eyes. The monocular PRL of the better eye has different characteristics from that of the worse eye, but during binocular viewing the PRL of the better eye drives fixational control and may serve as the new reference position for the oculomotor system. We conclude that evaluating binocular function in patients with macular disease reveals important clinical aspects that otherwise cannot be determined solely from examining monocular functions, and can lead to better disease management and interventions.