Inferior oblique inclusion is a rare complication following lateral rectus surgery. It is caused by inadvertent incorporation of the inferior oblique muscle into the lateral rectus muscle during surgery. The authors demonstrate two cases of inferior oblique inclusion with different manifestations and suggest the detection and proper management of this rare complication.
From the Department of Ophthalmology (J-YL, J-YS), Hallym University College of Medicine; and the Department of Ophthalmology (S-HK), Korea University College of Medicine, Ansan, Korea.
The authors have no financial or proprietary interest in the materials presented herein.
Address correspondence to Seung-Hyun Kim, MD, Department of Ophthalmology, Korea University Ansan Hospital, 516, Gojan-dong, Gyunggi-do, 425-707, Republic of Korea. E-mail: firstname.lastname@example.org
Received: August 18, 2010
Accepted: October 28, 2010
Posted Online: November 23, 2010
Inferior oblique inclusion is a rare complication following lateral rectus surgery. It is caused by inadvertent incorporation of the inferior oblique muscles into the lateral rectus muscle during surgery. These results can be associated with either resection or recession of the lateral rectus muscle. Inferior oblique inclusion syndrome could present as postoperative strabismus with variable features.1–3 Its diagnosis can be challenging until it is revealed by exploration of the lateral rectus muscle that underwent surgery. We describe two interesting cases of the syndrome without vertical deviation and consider its diagnosis and management.
A 44-year-old man initially presented to our department due to outward deviation of the left eye. Twenty years ago, the patient had undergone lateral rectus recession and medial rectus resection in his left eye at another hospital for correction of his intermittent exotropia. Nine months prior to presentation to our clinic, he underwent reoperation for recurrent exotropia. The second surgery was 7-mm lateral rectus recession and 5-mm medial rectus resection in his right eye. He was referred to our strabismus clinic because the exotropia was more aggravated after the second surgery.
His best-corrected visual acuity was 20/20 in both eyes. The prism cover test revealed 35 prism diopters (PD) exotropia in his left eye at both distance and near. Significant exotropia in the primary position in the left eye and mild limitation of adduction in his right eye were observed preoperatively (Fig. 1, top).
Figure 1. (Top) There Was Manifest Exotropia in the Primary Position in the Left Eye and Mild Limitation of Adduction in the Right Eye. (Middle) Note the Abnormal Adhesion Between the Right Lateral Rectus (black Arrow) and Inferior Oblique (white Arrow) Muscles. (bottom) Six Weeks After Surgery, 10 Prism Diopters Exophoria Was Achieved and the Adduction of the Right Eye Was Improved.
On forced duction test under general anesthesia, adduction of the right eye was restricted. Tightness and thickness of the isolated right lateral rectus muscle were initially observed during surgery (Fig. 1, middle). The inferior oblique muscle with conjoined sheath was included. We released the abnormal adhesion between the lateral rectus muscle and inferior oblique muscle. After careful separation, the lateral rectus muscle was disinserted and then reattached to the bare sclera, free of inferior oblique muscle sheath. The recession amount was 16 mm from the limbus, 2 mm posterior to the previous insertion site. There was free adduction at the end of surgery.
We also performed 2.5-mm medial rectus resection in the same eye with postoperative adjustment. After surgery, 10 PD exophoria and normal version were obtained and well maintained until the last follow-up visit at 1 year after surgery (Fig. 1, bottom).
A 5-year-old girl presented to our department due to inward deviation of the right eye. Three months prior to presentation to our clinic, the patient had undergone 6-mm bilateral lateral rectus muscle recession at another hospital for correction of intermittent exotropia.
Her best-corrected visual acuity was 20/25 in her right eye and 20/20 in her left eye. The prism cover test revealed 50 PD esotropia at distance and near. A cycloplegic refraction test revealed values of +1.50 diopter sphere in her right eye and +1.00 diopter sphere in her left eye.
We performed 6-mm bilateral medial rectus recession on the patient. One day after surgery, the patient showed only esophoria of 2 PD. However, 30 PD esotropia recurred 1 month after surgery. This was aggravated to 45 PD esotropia at 3 months after surgery. At this time, the refractive value remained unchanged. Limitation of abductions of −2 in the right eye and −1 in the left eye was observed. However, vertical deviation was not noted (Fig. 2, top).
Figure 2. (Top) Three Months After 6-mm Bilateral Medial Rectus Recessions, Significant Esotropia in the Primary Position Was Seen. Limitation of Abduction of Both Eyes Was Noted, More Marked in the Right Eye than in the Left Eye. (Middle) Intraoperative Findings. Note Tight Adhesion Between the Right Lateral Rectus (black Arrow) and Inferior Oblique (white Arrow) Muscle (left). The Inferior Oblique Muscle Was Included in This Tight Adhesion. Note the Inferior Oblique Muscle After Dissection and Detachment from the Lateral Rectus Muscle (right). (Bottom) Note Orthophoria in the Primary Position and Improvement of Abduction in Both Eyes at 3 Months After Surgery.
Exploration of the right lateral rectus muscle revealed tight, extensive adhesion of the right inferior oblique muscle (Fig. 2, middle). We removed the abnormal adhesion between the lateral rectus and inferior oblique muscle. Three millimeters of the lateral rectus tendon-like “stretched scar” was resected, and the lateral rectus muscle was then advanced to the original position. The left inferior oblique muscle was also included in the fascial sheath of the lateral rectus muscle with tight adhesion. We also performed adhesiolysis and advanced the lateral rectus muscle to its original insertion.
After surgery, orthophoria was achieved and abduction was improved at postoperative day 1, and these improvements were well maintained until the last follow-up visit at 6 months postoperatively (Fig. 2, bottom).
Inferior oblique inclusion syndrome could produce variable horizontal or vertical deviation of the involved eye with limitation of duction on a restrictive basis.1–3 During performance of lateral rectus surgery, a muscle hook passed from the inferior quadrant frequently encounters the anterior fibers of the inferior oblique muscle. These fibers are often pulled forward toward the insertion of the lateral rectus muscle. Once the inferior oblique muscle fibers have been displaced, the function of the muscle naturally becomes altered.
In previous studies, most patients demonstrated a vertical deviation in the affected eye.2,3 Moen and Marsh3 suggested that the presence of a vertical deviation or a deficiency of vertical rotation is a significant predictor of inferior oblique inclusion into the lateral rectus muscle insertion. However, our cases presented with a form of aggravated exotropia or consecutive esotropia. Neither vertical deviation nor deficiency of vertical rotation was noted. Helveston et al.2 also showed two patients with inferior oblique inclusion without vertical deviation after bilateral lateral rectus recession. We could suggest that inferior oblique inclusion might not always cause vertical deviation and vary in the manifestation, as in this report.
Operative findings were similar in both of our cases, with tight adhesion between inferior oblique and recessed lateral rectus muscles. We could not clearly explain why one was secondary exotropia and the other was reversed with that operative finding. Regarding the first case, exotropia with restricted adduction manifested because a tight conjoined sheath formed with adhesion between the lateral rectus and inferior oblique muscles may pull the eyeball toward the lateral side. The adhesion could be partially proven by the forced duction test.
Rosenbaum and Santiago described two patients with acute esotropia resembling sixth cranial nerve palsy involving the lateral rectus muscle following inferior oblique muscle surgery.4 Similarly, we suggest that extensive adhesion between the lateral rectus and inferior oblique muscles could cause functional paresis of the lateral rectus muscle and that the function of the lateral rectus muscle in our second case may recover gradually after adhesiolysis in case 2. From a different point of view, the inclusion of the inferior oblique muscle was not directly responsible for the consecutive esotropia, but rather contributed to the faulty reattachment of the lateral recti and development of “stretched scar,” which was corrected only when the stretched scar was resected and the muscles advanced.
It has been recognized that reoperation to free the inferior oblique muscle often failed to reduce vertical deviations.2,3 However, simple release of the inferior oblique muscle included in the attachment of the lateral rectus muscle has recently had a significant impact on reducing vertical deviation.1 Also, our patients experienced resolved horizontal strabismus by the separation of two conjoined muscles, and correction has been stable during the follow-up period.
For proper diagnosis, we should raise our level of suspicion of the syndrome, which can be confirmed by surgical exploration based on clinical suspicion. Attention should be paid to development of unexpected horizontal or vertical deviation after first or second strabismus surgery.
- Cline R, Valenzuela MD, Sketchley M. Vertical deviation improved with release of postoperative inferior oblique muscle inclusion. J AAPOS. 2005;9:184–188. doi:10.1016/j.jaapos.2004.11.020 [CrossRef]
- Helveston EM, Alcorn DM, Ellis FD. Inferior oblique inclusion after lateral rectus surgery. Graefes Arch Clin Exp Ophthalmol. 1988;226:102–105. doi:10.1007/BF02173291 [CrossRef]
- Moen C, Marsh IB. Inferior oblique syndrome: an under-recognised complication of strabismus surgery. Eye. 1998;12:970–972.
- Rosenbaum AL, Santiago AP. Inferior oblique weakening procedure: technique and indication. In: Isenberg SJ, Apt L, eds. Clinical Strabismus Management (Principles and Surgical Techniques). Philadelphia: W. B. Saunders; 1999:456–457.