Differentiating Paretic From Restrictive Etiologies of Diplopia
Restriction of eye movements should be strongly suspected in patients with proptosis, enophthalmos, or a history of orbital trauma or eye surgery. The most common causes of restrictive strabismus are thyroid eye disease and orbital trauma; these conditions are typically associated with orbital signs and symptoms. Diplopia in these patients may have both neural and restrictive components, especially after trauma.
Paretic and restrictive syndromes may be distinguished by assessing saccadic speed. Paretic conditions reduce saccadic velocity, whereas restrictive conditions do not. If this method does not provide an answer, then the examiner may perform a forced duction test (Fig 7-3). A restrictive process produces a mechanical limitation of the range of eye movements that can often be felt by the examiner when forceps or a cotton swab is used to advance the limited eye movement. In rare cases, chronic neural lesions may also cause mechanical limitation by gradual shortening of the unopposed antagonist muscle; therefore, a “tight” muscle may give a false-positive result.
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.