Adduction deficits common in patients with exotropia
Patients with consecutive exotropia tend to have limited adduction, a recent study has found. Moreover, more severe preoperative adduction deficits may lead to medial rectus muscle insertion abnormalities and abnormal forced ductions.
“Severe medial rectus muscle insertion abnormalities, including lost muscles, may be found despite mild preoperative adduction deficits,” researchers said.
A retrospective cohort study was conducted involving patients undergoing surgery for consecutive exotropia to analyse the relative frequency of adduction deficit grades and of abnormal anatomic findings. A scale ranging from ‒5 (severe limitation) to 0 (normal) was used to grade preoperative duction deficits.
Researchers reviewed operative reports to classify intraoperative factors: (1) medial rectus muscle attachment type (normal, abnormal [slipped or stretched scar], attached to pulley, behind pulley or mixed [a tenuous normal attachment, but with muscle fibers also attached to the pulley or behind the pulley]), (2) medial rectus muscle distal fibre location (millimetres from original insertion) and (3) lateral rectus muscle tightness (normal, mild or moderate restriction).
Adduction deficit was present in 124 (87 percent) of 143 eyes. There were worse adduction deficits found in eyes with abnormal (n=23), pulley (n=9), behind pulley (n=8) or mixed (n=7) attachments than normal attachments (n=96; p<0.02).
Distal medial rectus muscle fibre location (0 to 19.5 mm recessed) was significantly associated with a grade of adduction deficit (p<0.0001). Eyes with mild or moderate lateral rectus muscle tightness on forced duction testing (n=48/143 eyes) had worse adduction deficits than those without tightness (p<0.001).
Despite this overall association, a considerable individual variability existed.
“For example, for −1 and −2 adduction deficits, medial rectus muscle attachment could be at the pulley, behind the pulley or include the pulley (19/87 eyes; 22 percent), and the lateral rectus muscle was tight in 36 of 87 eyes (41 percent),” researchers said.