This study was approved by the Institutional Review Board of Seoul National University Hospital in Korea. (No. 1802-082-923) This study protocol followed the tenets of Declaration of Helsinki.
The medical charts of 37 consecutive patients (55 eyes) with superior oblique overaction, who underwent a superior oblique weakening procedure (superior oblique posterior tenectomy or superior oblique suture spacer) between January 2010 and June 2017 were retrospectively reviewed. Superior oblique posterior tenectomy was performed between January 2010 and August 2013, while the superior oblique suture spacer was performed between September 2013 and June 2017. As we believed that it would be better to avoid removing part of the muscle, a suture spacer was instead considered for the surgical techniques. All surgeries were performed by the same surgeon (SJK). Patients with superior oblique overaction associated with exotropia and esotropia were included. Those with Brown syndrome and double elevator palsy were excluded. While patients with primary superior oblique overaction were included in this study, those with secondary superior oblique overaction due to inferior oblique paresis were excluded. We also excluded patients with a history of vertical rectus muscle surgery or oblique muscle surgery.
The following patient characteristics were recorded: sex, age during surgery, refractive error determined using cycloplegic refraction, angle of deviation at a distance, dissociated vertical deviation, preoperative and postoperative superior oblique overaction, and fundus torsion were assessed using fundus photography.
The prism and alternate cover test were performed at 6 m for cooperative patients, and the Krimsky test was performed for uncooperative patients.
Superior oblique overaction was graded using a 6-point scale ranging from +0.5 to +3. During testing for the version of both eyes, the patients were instructed to look downward and 30° laterally in both directions. When both eyes were parallel, they were considered normal and without superior oblique overaction. However, when the adducted eye was directed vertically downward, the superior oblique overaction was defined as grade 3+. The intermediate ranges were graded 1+ and +2, respectively. A grade of +0.5 was assigned in cases of minimal overaction.
The dissociated vertical deviation was distinguished by observation of the following: (1) characteristic elevation and excyclotorsion of the involved eye under cover and (2) absence of hypotropic movement of the other eye in any field of gaze. All measurements were made by the same observer (SJK).
Cycloplegic refraction was performed with 1% cyclopentolate hydrochloride. Refractive errors measured by cycloplegic refraction were recorded as spherical equivalents.
Ocular torsion was assessed by fundus photography, and Retcam (RetCam Clarity Medical Systems Inc, Pleasanton, CA) before the surgery. Retcam was conducted in pediatric patients who were unable to cooperate with patients laying in a supine position while under chloral hydrate-induced sedation. The amount of ocular torsion was determined by measuring the disc fovea angle (DFA), using public domain software (Image J ; National Institutes of Health, Bethesda, MD). The DFA is defined as the angle between a horizontal line extending from the center of the optic disc and a line from the center of the disk to the fovea.
Stereopsis was measured using the Titmus Fly Stereo Test (Stereo Optical, Chicago, IL), in cooperative patients, before and after surgery.
All surgical procedures were conducted by the same surgeon (SJK) under general anesthesia. Surgical success was defined as the complete absence of superior oblique overaction 1 month after surgery. Failure of operation was defined as the incomplete reduction or elimination of superior oblique overaction after surgery.
We evaluated the success rate and factors influencing surgical response, by comparing the data of patients who underwent the unilateral and bilateral superior oblique muscle weakening procedures. We also compared the surgical success rate and factors, according to the procedure (posterior tenectomy, suture spacer). Finally, we compared the difference between the surgical success and failure groups. Statistical analyses were performed using SPSS Statistics 19.0 (IBM Corp., Armonk, NY). P<0.05 was considered to be statistically significant. The independent t-test, chi-square test, Fisher’s exact test, and the Mann-Whitney U test were used for statistical analyses.