Convergence Weakness with Intact Medial Rectus Function in Proptosis due to Orbital Tumors

Background: The pathway underlying ocular convergence is less clear. Convergence weakness is usually a clinical sign of dorsal midbrain pathology. An orbital tumor causing such phenomenon is unknown. We describe its occurrence in patients with proptosis due to orbital tumors. Materials and Methods: Series of six patients with axial proptosis secondary to orbital tumors that demonstrated varying forms of convergence weakness (deficiency to complete failure). Results: Three had weakness of convergence with drifting away of proptosed eyeball on attempted near vision, while the other three had failure. One of these had convergence weakness in nonproptosed eye. MRI excluded a central etiology in all. Conclusions: The article highlights an interesting phenomenon of deficient convergence in the presence of intact medial rectus function in patients with proptosis. The symmetry of orbital contents possibly plays a significant role in the process of convergence.