A Case of Congenital Absence of the Superior Oblique Muscle.

Purpose: To report a patient with adsence of the superior oblique (SO) muscle of the right eye, who showed improvement after surgery for hyperdeviation and exotropia. Methods: A four-year-old girl who presented with 14 PD exotropia, and 25 PD hypertropia of the right eye had a history of myectomy of the right inferior oblique (IO) muscle for bilateral SO palsy as a two-year-old. At the time of surgery, severely fibrotic pseudotendon of IO and Tenon's capsule attached to the insertional area of the inferior rectus muscle was found. IO was remyectomized with adhesiolysis. Lateral rectus and superior rectus (SR) muscles were recessed 6.5mm and 7mm, respectively. After exposure of SR, the absence of SO was found. MRI taken at postoperative one day showed definite SO absence. Results: Three weeks after surgery, 4 PD of left hyperphoria at distant and 5 PD of left hyperphoria at near were observed. Right hyperdeviation was not detected. At postoperative 7 months, 4 PD of exophoria, 6 PD of right dissociated vertical deviation (DVD) and 10 PD of left DVD were seen at distant. A small left hyperdeviation was intermittently noted at upgaze and was cautiously followed. Conclusions: Absence of the superior oblique muscle is rare. However, such absence should be suspected when apparent superior oblique palsy accompanies with severe hyperdeviation and horizontal deviation. MRI or CT is helpful in the diagnosis of this condition and direct confirmation is needed.