High Inferior Rectus Muscle Thickness, Limited Depression Predict A Pattern Strabismus

Increased inferior rectus muscle thickness and limited depression in eyes that undergo inferior rectus recession to treat Graves orbitopathy are predictors of A pattern strabismus postoperatively, according to research published in Acta Ophthalmologica. 

Patients undergoing inferior rectus recession or simultaneous inferior rectus recession to combat the effects of Graves orbitopathy (GO) were monitored for A pattern strabismus (defined as a ≥5° difference in squint angle between the primary gaze and downgaze). Results were collected from January 2010 to January 2020 at the University of Amsterdam or the University Eye Clinic Essen in Germany. 

Participants who were determined to have A pattern strabismus 3 months postoperatively were selected for analysis and demographic information (sex, age, date of operation, and previous medical history) and the following measurements were collected preoperatively and at the time of analysis: squint angle, cyclodeviation, ductions, and extraocular muscle thickness. Analysis was conducted to determine risk factors for and incidence rate of A pattern strabismus following recession surgery. 

The study took into account 590 participants who underwent inferior rectus recession. Nearly a third (32%) required simultaneous inferior rectus recession, and 10% developed A pattern strabismus, resulting in significant incyclotorsion (P =.000) and decreased depression 3 months postoperatively (P =.000) compared with controls. 

Compared with controls, the A pattern strabismus group had higher mean recession (3.91±1.37 mm vs 4.38±1.53 mm, P =.032, respectively), decreased depression (57.3±4.4° vs 50.2±7.4°, P =.045, respectively), increased thickness of the inferior rectus muscle (P =.027), and no significant difference in thickness of superior oblique muscle (P =.870). 47% of participants required additional surgery to improve their vision. 

“A significant A pattern arose during 10% of all inferior rectus recessions performed in the GO patients in this series, which led to further surgery in approximately half of the patients,” the investigators explain. “More severe thickening of the inferior rectus muscles was related to the A pattern. In addition to the thickness of the inferior rectus muscle, limited depression prior to inferior rectus recession and a greater amount of muscle recession predicted the occurrence of the A pattern.”

More severe thickening of the inferior rectus muscle is a risk factor for A pattern strabismus and low levels of depression and increased muscle recession are predictors for A pattern strabismus. 

They suggest minimizing inferior rectus recession when possible and paying close attention to the thickness of inferior rectus muscle and depression during surgery.