Caution in Clinical Interpretation of Near Point of Convergence: Influence of Time of Day on Oculomotor Function
Coon S, Bevilacqua ZW, Ferris M, Chen Z, Kawata K. Athl Train Sports Health Care. 2021;13(1):7-10
A person’s near point convergence measure may change ~1 cm from morning to night.
Medical professionals often measure near point of convergence (NPC) to help determine a concussion diagnosis because many athletes exhibit some form of visual dysfunction following a concussion. However, mechanical forces are not the only factors contributing to NPC changes. Fatigue from sleep deprivation can increase NPC measures. Currently, there is no research to determine the extent to which time of day influences NPC scores.
The authors evaluated whether NPC differs between a morning or nighttime assessment among healthy adults.
The authors assessed 30 participants (47% female; ~20 years of age) who slept ~7 hours. They monitored each participant’s sleep with an ActiGraph device for 7 days before the NPC measures. The authors then measured NPC at 7AM and 7PM with an NPC accommodation ruler and documented the average of 2 measures.
Overall, the participants recorded ~7.5 hours of sleep each night for a week. The estimated difference in NPC measures between 7AM (~5.3 cm) and 7PM (~6.4 cm) was about 1cm.
The authors of this study found a 20% increase in NPC scores from morning to night. However, this slight change may not be clinically meaningful. Many of the participants likely remained near a normal range of NPC scores (< 5 cm). Hence, at either time of day, the NPC may similarly perform when trying to detect a concussion; however, this should be confirmed in future studies. On average, participants experienced a 1 cm of change, with some people improving up to 1 cm and others worsening up to 4 cm. It would be interesting to know why some people experienced larger changes than others. However, it is reassuring that these changes are less than what some clinicians consider meaningful (> 4 cm), although this is based on only one study. Until we better understand how much change is meaningful and why some people experience large changes, it may be beneficial to retest patients at a similar time as an initial assessment.
Medical professionals should be aware that NPC scores increase due to ocular fatigue. While this may have a minimal impact on concussion detection, it could influence repeated assessments that influence return to play decisions.
Questions for Discussion
Do you use NPC scores to diagnose participants with a possible concussion? Do you note time of day when you take concussion measures?
- Near Point Convergence Is Worsened with Intense Subconcussive Impacts
- See All About It! New Set of Tests to Add to the Concussion Assessment Protocol
Written by: Jane McDevitt
Reviewed by: Jeffrey Driban