Forced Duction, Active Force Generation, and Saccadic Velocity
In the forced duction test, the eye is moved into various positions with the use of forceps to detect resistance to passive movement. This is usually done intraoperatively but can be done in clinic with topical anesthesia in cooperative patients.
In the active force generationtest, the awake patient is asked to move a topically anesthetized eye while the examiner grasps it with forceps. If the muscle tested is paretic, the examiner feels less-than-normal tension.
Saccadic velocity can be measured with instruments that track and record eye movement (eg, using magnetic search coils or video-based eye tracking). This measurement is useful for distinguishing paresis from restriction. For paretic muscles, saccadic velocity is low throughout the movement, whereas for restricted muscles, the velocity is initially normal but drops rapidly when the eye reaches the limit of its excursion. Clinical observation of saccadic velocity is qualitative: slow, “floating” saccades indicate muscle paresis.
See also BCSC Section 5, Neuro-Ophthalmology.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.