Session: Free papers Session III - Incomitant Strabismus

Superior rectus – lateral rectus co-contraction syndrome

Introduction

Exotropia, which is small in primary position, but increases significantly in up gaze has been termed ‘Y’ pattern strabismus. A specific variant of this pattern of strabismus has been termed pseudo-inferior oblique overaction. We report a case series of subjects that fulfill the criteria for aberrant mis-innervation of the lateral rectus muscle, resulting in exotropia manifested in up gaze. 

Methods: A retrospective review of patients evaluated for Y or T pattern exotropic strabismus. All patients had exotropic strabismus, absence of hypertropia in side gaze and normal sensory binocular status. Video documentation of the pathognomonic co-contraction phenomenon was recorded for 8. Surgery correction for the exotropia in up gaze in 5 subjects consisted of lateral rectus supra-placement with or without simultaneous recession. 

Results: Thirteen subjects fit the criteria for SR-LR co-contraction syndrome. 10 were female. Mean age at diagnosis was 7.4 years (± 4.7 years). Eight were classified as Y pattern with exotropia (mean 16pd) in primary position, and 5 were classified as T pattern exotropia with no deviation in primary. Mean deviation in up gaze was 22pd (±11pd). 2 were noted to have an esotropia in one horizontal side gaze position prior to surgery. 5 were noted to have compensatory head position. Mean age at surgery was 10 years. One patient required reoperation for the development of symptomatic exotropia in downgaze. Mean follow-up for all subjects was 5.5 years (±3.5 years). 

Conclusions: In this select group of subjects with SR to LR co-contraction, segregate into Y or T pattern strabismus. Further, we show with video that activation of the superior rectus creates an abducting force on the eye, signifying co-contraction of the ipsilateral lateral rectus muscle. Typically asymmetric or unilateral in nature, creating a compensatory head posture. Additionally, asymmetric recession of the lateral rectus muscles at the time of surgery may be indicated.