Caution in Clinical Interpretation of Near Point of Convergence: Influence of Time of Day on Oculomotor Function

Abstract

Purpose: To test whether near point of convergence (NPC) is stable across morning to night. Methods: Thirty healthy adults with an average sleep duration of 7 hours or more at night were recruited. The study used time (7 AM and 7 PM) as the independent variable and NPC as the outcome variable. To objectively assess one's average sleep duration, participants wore an activity/sleep tracker (ActiGraph) for 7 days prior to the study. NPC was measured by using an accommodative ruler with a target approaching participants' eyes at a speed of 2 cm/sec. Measurements were recorded when the participant reported experiencing diplopia or malalignment of the eye was observed. The assessment was repeated twice. Mean NPC (cm) was used for analyses. Results: NPC at 7 PM (6.35 ± 2.37 cm) was significantly worse compared to 7 AM (5.27 ± 2.00 cm, NPC at 7 PM (6.35 ± 2.37 cm) was significantly worse compared to 7 AM (5.27 ± 2.00 cm, P