Context: The effects of osteopathic cranial manipulative medicine (OCMM) on visual function have been poorly characterized in the literature. Based on a pilot study conducted by their research group, the authors conducted a study that examined whether OCMM produced a measurable change in visual function in adults with cranial asymmetry.

Study design: Randomized, controlled, double-blinded clinical trial. The intervention and control (sham therapy) were applied during 8 weekly visits, and participants in both groups received 8 weekly follow-up visits.

Participants: Adult volunteers aged between 18 and 35 years with unremarkable systemic or ocular history were recruited. Inclusion criteria were refractive error between 6 diopters of myopia and 5 diopters of hyperopia, regular astigmatism of any amount, and cranial somatic dysfunction.

Intervention: All participants were evaluated for cranial asymmetry and randomly assigned to the treatment or sham therapy group. The treatment group received OCMM to correct cranial dysfunctions, and the sham therapy group received light pressure applied to the cranium.

Outcome measures: Preintervention and postintervention ophthalmic examinations consisted of distance visual acuity testing, accommodative system testing, local stereoacuity testing, pupillary size measurements, and vergence system testing. A χ2 analysis was performed to determine participant masking. Analysis of variance was performed for all ophthalmic measures.

Results: Eighty-nine participants completed the trial, with 47 in the treatment group and 42 in the sham therapy group. A hierarchical analysis of variance revealed statistically significant within-groups effects (P<.05) from before the intervention to visit 16 in distance visual acuity of both eyes, local stereoacuity, Donder pushup in both eyes, and near point of convergence break and recovery. For treatment group vs sham therapy group, a statistically significant effect (P<.05) was observed from before the intervention to visit 16 in pupillary size under bright light in the left eye and in near point of convergence break.

Conclusion: Osteopathic cranial manipulative medicine may affect visual function in adults with cranial asymmetry. Active motion testing of the cranium for somatic dysfunction may affect the cranial system to a measurable level and explain interrater reliability issues in cranial studies.