Binocularly Asymmetric Crowding in Glaucoma and a Lack of Binocular Summation in Crowding

Abstract

Purpose Glaucoma is associated with progressive loss of retinal ganglion cells. Here we investigated the impact of glaucomatous damage on monocular and binocular crowding in parafoveal vision. We also examined the binocular summation of crowding to see if crowding is alleviated under binocular viewing. Methods The study design included 40 individuals with glaucoma and 24 age-similar normal cohorts. For each subject, the magnitude of crowding was determined by the extent of crowding zone. Crowding zone measurements were made binocularly in parafoveal vision (i.e., at 2° and 4° retinal eccentricities) visual field. For a subgroup of glaucoma subjects ( n = 17), crowding zone was also measured monocularly for each eye. Results Our results showed that, compared with normal cohorts, individuals with glaucoma exhibited significantly larger crowding—enlargement of crowding zone (an increase by 21%; P < 0.01). Moreover, we also observed a lack of binocular summation (i.e., a binocular ratio of 1): binocular crowding was determined by the better eye. Hence, our results did not provide evidence supporting binocular summation of crowding in glaucomatous vision. Conclusions Our findings show that crowding is exacerbated in parafoveal vision in glaucoma and binocularly asymmetric glaucoma seems to induce binocularly asymmetric crowding. Furthermore, the lack of binocular summation for crowding observed in glaucomatous vision combined with the lack of binocular summation reported in a previous study on normal healthy vision support the view that crowding may start in the early stages of visual processing, at least before the process of binocular integration takes place.

Foveal crowding appears to be robust to normal aging and glaucoma unlike parafoveal and peripheral crowding

“…A recent study done by our group also demonstrated an enlarged crowding zone in the parafoveal vision (i.e. 2 degrees and 4 degrees eccentricities) of patients with glaucoma compared with age-matched healthy controls ( Shamsi, Liu, & Kwon, 2022 ). Furthermore, comparing the crowding zone between the worse and the better eyes of patients with glaucoma indicated that eyes with more severe glaucomatous damage have a larger crowding zone, further highlighting the impact of glaucomatous damage on crowding.…”

“…The average crowding zone for the three groups was compared at the foveal (<0.25 degrees eccentricity), parafoveal (2 degrees and 4 degrees eccentricities), and peripheral (8 degrees and 10 degrees eccentricity) retinal locations. Values of crowding zone for glaucoma and old healthy subjects were reported in studies by Shamsi et al ( Shamsi, Liu, & Kwon, 2022 ; 2 degrees and 4 degrees eccentricity) and Ogata et al ( Ogata et al, 2019 ; 10 degrees eccentricity). For old versus young normally sighted subjects, the crowding zone data were obtained from a study by Liu et al ( Liu et al, 2017 ; 2 degrees, 4 degrees, and 8 degrees eccentricities).…”

“…As demonstrated in Figure 2 A(ii), there seems to be a lack of evidence for age-related or glaucoma-related changes in the extent of foveal crowding. On the other hand, in parafoveal and peripheral vision, the crowding zone is significantly larger in glaucoma versus old healthy control groups ( Shamsi, Liu, & Kwon, 2022 ) and in old versus young normally sighted subjects ( Liu et al, 2017 ; all p values < 0.01). These results further confirmed the presence of both age-related and glaucoma-related changes in parafoveal and peripheral crowding despite some obvious methodological differences among studies.…”

“…Next, in order to put our foveal crowding results into perspective, we visualized both age-related and glaucoma-related changes in crowding zone at different eccentricities, including foveal vision using the data obtained from both the current study and previously published studies ( Liu et al, 2017 ; Ogata et al, 2019 ; Pelli et al, 2016 ; Shamsi, Liu, & Kwon, 2022 ). Figure 2 A(ii) shows a plot of crowding zone as a function of eccentricity for glaucoma (orange triangles, mean age = 65.21 years old), old healthy control (green squares, mean age = 60.08 years old), and young healthy control groups (gray circles, mean age = 22.6 years old).…”

“…Glaucoma is one of the leading causes of irreversible blindness worldwide ( Tham, Li, Wong, Quigley, Aung, & Cheng, 2014 ) and characterized by progressive death of retinal ganglion cells and optic nerve fibers. Studies have shown that patients with glaucoma exhibit increased crowding in both parafoveal and peripheral vision ( Ogata, Boer, Daga, Jammal, Stringham, & Medeiros, 2019 ; Shamsi, Liu, & Kwon, 2022 ). For example, Ogata et al ( Ogata et al, 2019 ) reported that the crowding zone in the peripheral vision (10 degrees eccentricity) of patients with glaucoma was significantly greater than that of normally sighted controls.…”