Patients
This study was approved by the Institutional Review Board of Korea University Medical Center. It adhered to tenets of the Declaration of Helsinki. Written informed consent was obtained from all patients and their guardians. We retrospectively reviewed the medical records of 98 consecutive patients with congenital USOP diagnosed between 2001 and 2015 at the Department of Ophthalmology, Korea University Medical Center. The diagnosis of USOP was based on hypertropia, apparent elevation and under-depression in adduction of the paretic eye, anomalous head posture, or a positive Bielschowsky head-tilt test. All enrolled patients underwent full ophthalmic examination including visual acuity, refraction test, ocular movement, fixation preference,18 scale of superior oblique underaction (SOUA) and inferior oblique overaction(IOOA), angle of deviation in the alternate prism cover test (prism diopters, PD), the Bielschowsky head-tilt test, presence of amblyopia or dissociated vertical deviation (DVD), and fundus examination.
Amblyopia was defined as a best-corrected visual acuity of 6/9 or worse that was not directly attributable to any underlying structural abnormality of the eye or visual pathway. The exclusion criteria included acquired (masked) bilateral superior oblique palsy during ophthalmic examination, previous ocular surgery, history of head trauma, cerebrovascular diseases, and neurological disorders.
Measurements
The SOUA and IOOA were assessed using a −4 to +4 scale. The minus and plus values indicate underaction and overaction, respectively. The scales were documented before the operation and at each postoperative visit. SOUA was graded from −1 to −4 as follows: −1, mild downward deviation of the pupil from the horizontal line in adduction; -2, lower margin of the pupil was aligned to the margin of the lower lid in adduction; -3, inferior half of the pupil was covered by the lower lid in adduction; and -4, the entire pupil was covered by the lower lid in adduction. IOOA was graded from +1 to +4 as follows: +1, mild upward deviation of the pupil from the horizontal line in adduction; +2, upper margin of the pupil was aligned to the margin of the upper lid in adduction; +3, superior half of the pupil was covered by the upper lid in adduction; and +4, the entire pupil was covered by the upper lid in adduction.
Fundus examination was performed to measure the degree of excyclotorsion using a fundus camera (TRC-50DX, Topcon Medical System, Tokyo, Japan) or indirect ophthalmoscope before and after the operation. The degree of excyclotorsion was measured using the Guyton grading scale.19 Values +1 to +4 represent excyclotorsion and values −1 to −4 represent incyclotorsion based on the classification. When a horizontal line passed through the fovea within the inferior one-third of the disc, it was considered a normal range of torsion. If the vertical position of the fovea was located below the center of the optic disc, the excyclotorsion was graded from +1 to +4.
Surgical procedures performed in this study included inferior oblique recession (12–14 mm) or ipsilateral superior rectus recession with or without superior rectus recession (>15 PD of hypertropia in the primary position) based on the preoperative amount of hypertropia at the primary position. Postoperative examinations were performed at 1, 3, 6, and 12 months, and then routinely at 1-year intervals. All measurements were compared between pre- and postoperative final visits. Patients who were followed-up for at least 6 months postoperatively were included.
All patients were divided into the accordance (preoperative fundus ocular excyclotorsion in the paretic eye) and discordance (preoperative ocular excyclotorsion in the non-paretic eye) groups. The pre- and postoperative clinical features and the degree and change in excyclotorsion were compared between the accordance and discordance groups.
Statistical analysis
Statistical analysis was conducted using SPSS version 21.0 (IBM Corporation, Armonk, NY, USA). To assess the differences between the two groups, we used the Mann–Whitney test and Fisher’s exact test. Statistical significance was set at p < 0.05.