Abstract
Glaucoma is a leading cause of blindness worldwide, characterized by progressive loss of retinal ganglion cells. Despite good photopic visual acuity, glaucoma patients report difficulty performing daily activities under dim light, including central vision tasks like reading. Despite these reports, no study has examined reading in glaucoma patients under mesopic conditions. Thus, the current study was undertaken to evaluate the effect of mesopic light conditions on reading vision of glaucoma. The study included 29 glaucoma patients (mean age: 67 yrs; mean deviation of the worse eye and better eye: -12 dB vs. -6 dB), 10 older controls (mean age: 68 yrs), and 31 young controls (20 yrs). Reading performance was tested on the MNREAD iPad app under mesopic (2 cd/m2) and photopic (200 cd/m2) conditions. Four reading indices: Maximum Reading Speed (MRS), Critical Print Size (CPS), Reading Acuity (RA), Reading Accessibility Index (RAI), were obtained from the MNREAD test yielding a plot of reading speed versus print size. We found that compared to photopic conditions, both normal controls and glaucoma patients exhibited noticeable decreases in reading vision under mesopic conditions. However, the decrease was more pronounced in glaucoma patients: under mesopic conditions, MRS and RAI of glaucoma patients decreased by 10% and 13% (ps<0.005); CPS and RA were enlarged by 75% and 129% (ps<0.001). Moreover, under both photopic and mesopic conditions, reading vision of glaucoma patients was worse than that of normal controls but the difference was greater under mesopic conditions (ps<0.05). Our results demonstrate that mesopic conditions make reading more effortful for both normal controls and glaucoma patients. However, reading in dim light appears to be more burdensome for glaucoma patients. Our findings highlight that mesopic reading tests mediated by both cone and rod vision likely provide a more comprehensive assessment of a patient’s reading ability in daily life.