Boris Penaloza¹ (), MiYoung Kwon¹; ¹Northeastern University

While most research evaluates visual function under photopic (bright daylight) conditions, mesopic environments, such as dimly lit rooms or nighttime settings, pose real-world visual challenges. Older adults, despite having normal photopic visual acuity, often report significant difficulty with daily visual activities like reading or navigation in low-light conditions. Mesopic vision relies on both rod and cone photoreceptors, making it more susceptible to age-related retinal and optical changes, such as reduced pupil size, rod-photoreceptor loss, and optical opacity. However, age-related changes in visual function under mesopic conditions remain poorly understood. Here we investigate how aging affects reading vision and the functional field of view (FFV - the spatial extent of the visual field relevant to everyday tasks) under photopic and mesopic conditions. Using the MNREAD iPad app, we evaluated mesopic (2 cd/m²) and photopic (220 cd/m²) reading vision in 157 participants aged 18–84. Reading vision, indicated by maximum reading speed, critical print size, and reading acuity, declined linearly across adulthood, from the 20s to the 80s, with significantly steeper declines observed under mesopic conditions (p<0.001). A similar pattern was observed when FFV was assessed under divided attention: FFV was significantly reduced in older adults compared to young adults under both photopic and mesopic conditions (p<0.01). However, older adults experienced even greater reductions in FFV (p<0.01) under mesopic conditions. Our findings demonstrate the added burden of dim light on the aging population, thereby highlighting the critical need to assess the interplay between aging and mesopic conditions on functional vision. Understanding these interactions can inform the design of lighting solutions, accessibility measures, and targeted interventions to mitigate age-related visual decline and improve quality of life for older adults.