The Relationship Between Daytime and Nighttime Stereoacuity

Good stereoacuity in a wide range of illumination conditions is important for professionals such as surgeons and pilots. Most stereoacuity measures are conducted in daylight viewing conditions, providing information about daytime stereoacuity, whereas less is known about nighttime stereoacuity and the relationship between them. In the current study, we designed two computerized stereopsis tasks to be conducted in low-illuminance conditions. We compared daytime and nighttime stereoacuity, as measured using a Functional Visual Analyzer (FVA), a clinical screening tool. The first task, which was modified from the FVA’s setting, required participants to detect which one of four circles was on a different depth plane. The second task required participants to determine whether a target line presented at varying depths was in front of or behind a comparison line on a fixed plane. For both tasks, stereoacuity was defined as the minimum binocular disparity at which a participant could perform the tasks. We recruited 53 participants aged 22–40 (M = 26.06 ± 4.28) with no ocular diseases and visual acuity better than 20/25. The FVA measures showed no significant difference between daytime and nighttime stereoacuity (M ± SD = 31.70 ± 16.73, 33.58 ± 27.86; t = −.538, p = .593), but they were positively correlated with each other (r = .433, p = .001). The thresholds measured in both tasks correlated significantly with nighttime stereoacuity (r = .323, p = .018; r = .300, p = .029), but only the first task correlated with daytime stereoacuity (r = .275, p = .046; r = .101, p = .470), indicating that the tasks conducted in the current setting were suitable for measuring nighttime stereoacuity. The results further indicate that the underlying mechanism for nighttime stereoacuity might differ from that of daytime stereoacuity and cannot be assessed using existing clinical screening tools.