Masked bilateral superior oblique palsy in children

Purpose: Following surgery on an eye for unilateral superior oblique palsy, it is a well-recognized postoperative occurrence for the unoperated eye to develop superior oblique palsy, commonly referred to as masked bilateral superior oblique palsy. The purpose of this study was to describe this postoperative finding in children following unilateral inferior oblique weakening surgery. Methods: A retrospective review of records of children who underwent unilateral inferior oblique weakening surgery at Children's Hospital of Michigan, Detroit, Michigan, from 1987 to 2005, including information on the development of masked bilateral superior oblique palsy with contralateral inferior oblique overaction requiring a second surgical intervention. Results: Of 50 children (25 boys and 25 girls, mean age: 5.6 years) who underwent unilateral inferior oblique weakening surgery (47 recessions and 3 myectomies), 9 (18%) manifested masked bilateral superior oblique palsy postoperatively, requiring subsequent surgical weakening of the inferior oblique muscle in the unoperated eye. Preoperative primary position hypertropia in children who were eventually diagnosed as having masked bilateral superior oblique palsy (5.56 ± 4.22 prism diopters [PD]) was significantly smaller compared to children with unilateral superior oblique palsy (10.4 ± 6.5 PD, P = .012), and preoperative primary position hypertropia of less than 5 PD was associated with an odds ratio of 8.2 (95% confidence interval: 1.7 to 38.5, P = .008) for requiring reoperation. Conclusions: Masked bilateral superior oblique palsy is a possible outcome after surgery for the correction of pediatric unilateral superior oblique palsy. Parents should be informed of this possible outcome, especially when primary position hypertropia is less than 5 PD.