Abstract Introduction Few in vivo studies have investigated the effect of maxillary expansion on strabismus; however, some in vitro studies hypothesized that changes in the palatal width obtained with rapid maxillary expansion appliances could involve other bone structures that contain blood vessels and nerves conveying to the orbital cavity. The present case report seems to support that hypothesis, even if no analysis of pathogenetic mechanisms could be drawn. Case presentation We present the case of a 14-year-old Caucasian girl affected by strabismus and referred for the treatment of a class III malocclusion with transverse maxillary deficiency, which was corrected by the application of a rapid maxillary expansion appliance (Haas type). At 2 months follow-up, the patient, who had not undergone any ophthalmologic treatment, was submitted to an ophthalmologic examination that revealed a marked change in the vision defect, which slightly relapsed at 6 months. Conclusions The results of our clinical evaluation showed a remarkable modification of the oculomotor system of our patient as an outcome of the rapid maxillary expansion. Further studies are needed to clarify these findings and to investigate the clinical implications of these observations.