A number of factors may help explain our observations. Several studies have investigated the relationship between glaucoma and cognitive impairment. Daveckaite et al. found that normal-tension glaucoma patients had lower cognitive function scores and performed worse in a specific drawing style more often than those with cataracts. Bulut et al. observed reduced cognitive performance (based on the Mini-Mental State Examination) in primary open-angle glaucoma patients and normal-tension glaucoma patients compared to the healthy group.