Determining near point of convergence: exploring a component of the vestibular/ocular motor screen comparing varied target sizes

Background Near point of convergence (NPC), a component of the Vestibular Ocular Motor Screening (VOMS) assessment, may be helpful in diagnosing concussion. The VOMS uses a standardized approach to measure NPC; however, methods of screening for NPC are not standardized. Purpose The purpose of this study was to determine whether four different methods of measuring NPC yielded different estimates. Study Design Descriptive within-subjects laboratory study. Level of Evidence Level 3. Methods Healthy recreational athletes participated in a comparison of 4 commonly used methods of measuring NPC: a 12-point font target, the VOMS (14-point font target), the tip of a black pen, and the Bernell Vergel™ device (9-point font target). The order of the presentation of the 4 targets was randomized. Results Seventy-five participants (59 females, 16 males; mean [SD] age=21.0 [6.12] years) completed 3 trials. The mean (SD) of the 900 NPC measurements was 7.11 (3.67) cm. Measurements for all targets had excellent reliability (r=0.94 to 0.98). In a comparative analysis, participant age was associated with NPC (p<0.01) and was covaried. The NPCs derived from both the 12-point and 14-point font targets were smaller than NPCs from the tip of the black pen and the 9-point font device (p<0.01). Measurements between the tip of the black pen and the 9-point font device (p=0.25) and between the 12-point and 14-point font targets (p=0.84) did not differ. Conclusions The method used to measure NPC as a screening test for concussion should be standardized because the estimate differs depending on the technique chosen. The current study supports previous findings that the type of target used to measure NPC should be standardized for concussion assessment.