Short-Term Effect of Spinal Manipulation on the Magnitude of EXOPHORIA in Adults Who Are Asymptomatic: A Randomized Controlled Trial

Abstract

Objective: This study aimed to assess the immediate and short-term effects of cervical spinal manipulation, compared with a placebo, on the magnitude of near and distance exophoria in adults with asymptomatic exophoria. Methods: In this single-blind, randomized controlled trial, individuals with a clinical diagnosis of horizontal exophoria confirmed with the prism alternating cover test (PACT) were allocated to a single intervention session using a high-velocity, low-amplitude cervical spinal manipulation technique or a sham intervention (manual contact under the head). Outcomes were the magnitude of horizontal heterophoria, as a measure of binocular vision efficiency at near (40 cm) or distance (4 m) fixation, using the PACT. Evaluations were made at baseline, immediately after intervention, and at a 1-week follow-up. Results: From May to September 2021, 44 volunteers (23 women), with a mean age of 35 (SD = 9.5) years, were recruited and equally distributed into the study groups. All participants completed follow-up assessments, and no adverse events were reported. There was a significant time x group interaction for exophoria at near vision, but not at distance fixation. The spinal manipulation group showed a significant decrease of near exophoria compared to the control group at the 1-week follow-up (mean difference = -1.09 prism diopters; 95% CI = -0.20 to - 1.98 prism diopters). Conclusion: The use of cervical spinal manipulation therapy resulted in a significant reduction of the magnitude of horizontal exophoria at near vision (medium effect size), compared with the placebo, in young adults who are asymptomatic. However, these effects were not observed at distance fixation and should be considered cautiously due to the pre-post design with a single intervention session and the short-term follow-up. Impact: The findings suggest short-term benefits of spinal manipulation therapy can manage undiagnosed ocular convergence disorders, although changes were not clinically relevant.