Eye movements may be restricted by congenital or acquired mechanical factors. Congenitally deficient neural innervation to extraocular muscles can also cause limited eye movements with a restrictive component.
Thyroid Eye Disease
The most common cause of restrictive strabismus in adults is TED. Any of the extraocular muscles may be involved, but the muscles most commonly affected are the inferior and medial recti. When the inferior rectus muscle is involved, an ipsilateral hypotropia typically occurs in primary position that increases in upgaze—the restrictive process pulls the eye down and limits supraduction. When the medial rectus is the affected muscle, an esodeviation typically occurs that increases on lateral gaze to the same side (the enlarged, “tight” medial rectus restricts abduction). The diagnosis of TED is straightforward if associated with proptosis, chemosis, eyelid retraction, and eyelid lag; however, restrictive strabismus may be the only sign. Forced duction testing (see Fig 7-3) may provide information to support this diagnosis. Neuroimaging results for patients with TED typically reveal enlargement of the extraocular muscle bellies with sparing of the tendons (see Chapter 4, Fig 4-16). For a more extensive discussion of TED, see Chapter 4 as well as BCSC Section 7, Oculofacial Plastic and Orbital Surgery.
Excerpted from BCSC 2020-2021 series: Section 5 - Neuro-Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.