Costenbader lecture. Anatomy and surgery of the inferior oblique muscle: recent findings

Anatomical Study of the Inferior Oblique Muscle and Its Innervation: Morphometric Characteristics, Anatomical Variations, and Histological Evaluation of the Nerve to the Inferior Oblique Muscle

BACKGROUND

This report aims to supplement the existing knowledge on the inferior oblique muscle. In particular, this study presents detailed anatomical and histological data concerning the muscle's entry point (or entry zone) of the nerve to the inferior oblique muscle. Particular attention was paid to the topographical relationships of the nerve to the inferior oblique muscle (NTIO), including the location of its entry point to the muscle's belly and its anatomical variations.

METHODS

Sixty orbits from cadaveric hemi-heads fixed in 10% formalin were studied. The course of the NTIO was traced along the lateral border of the inferior rectus muscle as far as its entry point to the inferior oblique muscle. Particular attention was paid to the various ways in which the NTIO's muscular sub-branches penetrated between the fibers of the inferior oblique muscle.

RESULTS

Three types of NTIO entries to the inferior oblique muscle's belly were distinguished. In the most common type (48.3%), the nerve entered the muscle's inferior (orbital) surface. In the next most common type (36.7%), terminal muscular sub-branches of the NTIO joined the superior (also referred to as ocular or global) surface of the inferior oblique muscle. In the remaining four cases (15%), the terminal sub-branches of the NTIO were divided into two main groups (superior and inferior) that joined both the superior and inferior surfaces of the muscle. Histological examination confirmed that the distal part of the NTIO shows a characteristic arcuate course (angulation) just before reaching the muscle's belly. The process for splitting and forming separate muscular sub-branches of the NTIO was observed for all the examined histological specimens at the level of the nerve's angulation.

CONCLUSIONS

The presented findings enhance the understanding of the anatomical variations and precise distribution of motor sub-branches reaching the inferior oblique muscle, which may deepen anatomical knowledge and potentially enhance the management of ocular motor disorders.

Modified inferior oblique anterior transposition for dissociated vertical deviation combined with superior oblique palsy: A case report

BACKGROUND

Inferior oblique anterior transposition (IOAT) has emerged as an effective surgery in the management of dissociated vertical deviation (DVD) combined with superior oblique palsy (SOP). Traditional IOAT usually provides satisfactory primary position alignment and simultaneously restricts the superior floating phenomenon. However, it also increases the risk of the anti-elevation syndrome and narrowing of the palpebral fissure in straight-ahead gaze, especially after the unilateral operation.

CASE SUMMARY

We report the outcomes of the modified unilateral IOAT in two patients with unilateral DVD combined with SOP. The anterior-nasal fibers of the inferior oblique muscle were attached at 9 mm posterior to the corneal limbus along the temporal board of the inferior rectus muscle, the other fibers were attached a further 5 mm temporal to the anterior-nasal fibers. Postoperatively, both hypertropia and floating were improved, and no obvious complications occurred.

CONCLUSION

In these cases, the modified unilateral IOAT was an effective and safe surgical method for treating DVD with SOP.

Long-Term Efficacy of Inferior Oblique Myectomy Accompanied with Tenon’s Capsule Closure: Objective Analysis Using Nine-Gaze Photographs

Background: The aim is to evaluate the long-term efficacy of inferior oblique (IO) myectomy combined with Tenon’s capsule closure to prevent muscle reattachment to the sclera. Methods: We retrospectively reviewed the medical records of 18 patients with primary and secondary IO overaction who underwent IO myectomy accompanied by Tenon’s capsule closure. Patients were followed up for at least 1 year after the surgery. The main outcome measures included oblique muscle dysfunction, which was objectively graded through computerized analysis of nine-gaze photographs, and the amount of vertical deviation in the primary position using alternate prism cover testing. Results: After a mean follow up of 2.5 years, the grade of IO overaction decreased from +2.2 ± 1.0 to −0.8 ± 1.0 (p < 0.001). In patients with secondary IO overaction with superior oblique (SO) palsy, SO underaction improved from −2.2 ± 1.5 to −0.2 ± 1.8 (p = 0.006). Successful vertical deviation in the primary position of seven prism diopters or less was achieved in 83.3% of the patients. Underaction of the IO was observed in 11.1% of patients, whereas none of the patients showed antielevation syndrome. Conclusion: IO myectomy combined with Tenon’s capsule closure might be safe and effective for the treatment of primary and secondary IO overaction in the long term.

Novel Inferior Oblique Muscle Y Splitting Procedure to Minimize the Anti-Elevation Syndrome: A Pilot Study

Purpose

To describe novel Y splitting procedure of inferior oblique muscle to mitigate the anti-elevation syndrome.

Methods

A pilot, prospective interventional study was undertaken to assess the effect of inferior oblique muscle Y-splitting in patients with unilateral 3+ or more overaction. To correct primary gaze hypertropia and the excyclotorsion, a Y-splitting procedure was performed (along with routine horizontal muscle surgery as per the deviation) in 14 subjects. The effect of surgery was assessed at baseline and at 6 months post-intervention.

Results

The mean age of 14 subjects was 25.14±7.70 years. The mean pre-operative hypertropia, excyclotorsion and inferior oblique muscle over-action was 18.42±3.50 PD, 14.14±2.65 degrees, and +3.21±0.42 respectively. Following surgery, this was reduced to 1.57±1.74 PD of residual hypertropia (a net correction of 16.85±2.31 PD, p = 0.005), 3.85±1.46 degrees of residual excyclotorsion (a net correction of 10.28±1.72 degrees, p < 0.05), and +0.28±0.46 of residual inferior oblique over-action (a net correction ~+3) at the end of 6 months. Amongst fourteen patients, three patients still experienced residual/variable anti-elevation effect, and during the study period none of them experienced any adverse event and none of them required any additional surgeries.

Conclusion

While anteriorizing the inferior oblique muscle to correct primary gaze hypertropia and the excyclotorsion, a novel “Y splitting” procedure can be followed to achieve the desired results with mitigated anti-elevation effect.

Retro-equatorial inferior oblique myopexy for treatment of inferior oblique overaction

AIM

To compare the effectiveness of inferior oblique retroequatorial myopexy and inferior oblique myectomy in correction of inferior oblique overaction (IOOA).

PATIENTS AND METHODS

This was a pilot study study including forty patients with primary IOOA of all grades, with or without primary position horizontal deviations. Patients were randomized to have either IO retroequatorial myopexy, group A, or IO myectomy, group B. Success was defined as elimination of the IOOA at 6 months postoperatively. Secondary outcome measures included residual or recurrent elevation in adduction, development of postoperative hypotropia in adduction, postoperative contralateral IOOA, major intraoperative complications, and reversibility of the procedure.

RESULTS

At 6 months postoperative, the success rate was higher in the myectomy group (76%) than in the myopexy group (58%); however, this difference was not statistically significant (P = 0.1). The incidence of residual IOOA in myopexy group was significantly higher in patients with higher preoperative grades of IOOA (P ˂ 0.001). While this difference was not statistically significant among patients in myectomy group (P = 0.09). Collapse of V-pattern was acheived in nine (69%) patients in myopexy group compared with 8 (57%) in myectomy group with a statistically significant difference (P ≤ 0.001). No patients in myopexy group developed postoperative hypotropia in adduction or postoperative contralateral IOOA, compared with eight (22%) patients of myectomy group (P = 0.002) who developed postoperative hypotropia and two (66.6%) patients with unilateral IOOA who developed contralateral IOOA in myectomy group (P ˂ 0.001). No intraoperative complications were encountered in either group. postoperative.

CONCLUSIONS

Retroequatorial myopexy of the inferior oblique is as effective as inferior oblique myectomy in eliminating lower and moderate grades of primary IOOA; however, it is more effective in collapsing V-pattern associated with IOOA, and is not associated with postoperative hypotropia or contralateral IOOA after unilateral surgery. It can be used as a safe, reversible alternative to myectomy; however, it is not suitable for high grades of IOOA.

Adherence syndrome following inferior oblique anteropositioning - a case report

INTRODUCTION

We report a case of inferior oblique (IO) muscle adherence with fat adherence, which developed following unilateral IO anteriorization (IOAT).

METHODS

A 14-year-old child with V pattern left exotropia, bilateral IO overaction, bilateral dissociated vertical deviation (DVD), and strabismic amblyopia (OS) underwent recess/resect procedure along with IOAT. He developed consecutive esotropia and drooping of upper eyelid with marked limitation of levoelevation (-4). Differential diagnoses of antielevation syndrome and adherence syndrome were considered. On surgical exploration, forced duction test (FDT) was positive for elevation, left inferior oblique (LIO) muscle insertion was found anterior to the inferior rectus (IR) insertion along with fat adhesions which were released and IO muscle was reattached 3 mm behind and 2 mm lateral to IR insertion, along with advancement of left lateral rectus.

RESULTS

Following resurgery, the patient had six prisms left esophoria and a hypotropia 9 prisms, with minimal limitation of levoelevation (-1). One month later, it was seen that the hypotropia had increased to 18 prism diopters and limitation of elevation was -2.

CONCLUSIONS

Adherence syndrome is a rare and severe complication of IO weakening procedures. The initial postoperative improvement achieved in elevation and hypotropia in primary position was not maintained over subsequent follow-ups.

Managing Hypoplasia of the Inferior Rectus Muscle by Inferior Oblique Anterior Transposition in Children

Congenital hypoplasia or aplasia of the inferior rectus muscle is an uncommon condition. The authors present two pediatric patients with hypoplasia of the inferior rectus muscle treated by inferior oblique anterior transposition. The long-term follow-up outcomes of eye position and stereopsis acuity development were favorable. [J Pediatr Ophthalmol Strabismus. 2017;54:e50-e53.].

Fat adherence syndrome following inferior oblique surgery: Treatment and outcomes

PURPOSE

Describe surgical treatment and results in a group of patients diagnosed and operated on of fat adherence syndrome following inferior oblique surgery.

PATIENTS, MATERIAL AND METHODS

Retrospective study of 6 cases diagnosed and treated of fat adherence syndrome following inferior oblique surgery. Mean age was 24.67 years (range, 5-41), 3 males, 5 unilateral and 1 bilateral. Mean vertical deviation was 16.16pd (range, 4-25). Esotropia was associated in 4 cases, diplopia in other 2, and anomalous head posture in 3. A good outcome was considered when the final deviation was less than 10pd, with mild limitation of elevation, without anomalous head posture, and a negative duction forced test.

RESULTS

The final vertical deviation was 6.83pd (range, 0-14). A 2-4mm inferior rectus recession was performed on 4 patients associated to an inferior oblique surgery/exploration. All patients were operated on once, except 1 case. A good outcome was achieved in 3 patients. Anomalous head posture was resolved in 2 of 3 cases. Diplopia resolved after surgery. Only one case achieved orthophoria. Mean evolution time was 34.83 months (range, 6-78).

CONCLUSION

In the treatment of the fat adherence syndrome, an inferior rectus recession is recommended, associated to inferior oblique exploration or surgery. A good favorable outcome was only achieved in half of the cases with surgical treatment. Limitation of elevation could not be completely resolved in any of the patients.

Infrequent Complications of Inferior Oblique Recession Surgery

PURPOSE

To report the infrequent complications, including antielevation and adherence syndrome, after a unilateral and bilateral inferior oblique (IO) recession procedure and to discuss the possible causes.

METHODS

A retrospective chart review was conducted for patients on whom unilateral or bilateral IO weakening surgeries were performed.

RESULTS

Forty-three patients were included in the study. In 23 patients unilateral and in 20 patients bilateral IO weakening was performed. All patients underwent IO recession surgery. Mild limitation of elevation developed in two patients and adherence syndrome developed in one patient. All occurred after unilateral IO recession. No duction deficiency was observed in patients after bilateral IO recession.

CONCLUSION

Antielevation and adherence syndrome can develop after unilateral IO recession surgery. Care should be taken not to tighten the neurofibrovascular bundle of the IO muscle during surgery.

Uses of the Inferior Oblique Muscle in Strabismus Surgery

Inferior oblique muscle weakening is typically performed for overaction of the muscle. In this article, we review inferior oblique muscle anatomy, different weakening procedures, and recent surgical techniques that take advantage of the muscle's unique anatomy for the treatment of additional indications such as excyclotorsion and hypertropia in primary gaze.

Restrictive strabismus: diagnosis and management

INTRODUCTION

Restrictive strabismus is a type of ocular misalignment with limitation of motility caused by intrinsic or extrinsic mechanical forces. The clinical spectrum of either purely or partially restrictive strabismus is very broad. Most cases are of congenital, traumatic, endocrine, post-paralytic or myopathic origin. The surgical treatment strategies are designed to correct abnormal head posture, to eliminate diplopia in primary and functional positions of gaze and to enhance aesthetic and psychosocial aspects of a patient's life.

PURPOSE

The objective of this paper is to present a clinical approach to the diagnosis and evaluation of patients with restrictive strabismus and to propose a logical surgical approach to the correction of this type of ocular misalignment.

PATIENTS AND METHODS

As representative of the broad spectrum of restrictive strabismus problems, twelve cases are presented and the preoperative and postoperative clinical finding are illustrated with photographs.

CONCLUSION

The clinical spectrum of either purely or partially restrictive strabismus is very broad. The clinical evaluation of patients with this problem must include a careful and detailed history, which is crucial to establishing the diagnosis and must also explore the patient's concerns. Analysis of fixation, head posture, and ocular alignment require both traditional and special examination techniques. Patient and surgeon expectations must be synchronized preoperatively. A variety of surgical strategies can be applied to improve head posture, eliminate diplopia, and improve cosmesis.

Graded anterior transposition of the inferior oblique muscle for V-pattern strabismus

PURPOSE

To evaluate the efficacy of bilateral graded anterior transposition of the inferior oblique muscle for the correction of V-pattern strabismus associated with inferior oblique overaction.

METHODS

Medical records of patients who underwent graded anterior transposition of the inferior oblique muscle for bilateral primary inferior oblique overaction associated with V-pattern strabismus were reviewed. The surgical technique entailed recessing and anteriorly transposing the inferior oblique muscle to various locations along the temporal border of the inferior rectus muscle. The amount of anterior transposition was determined by both the severity of the overaction and the extent of the V pattern. We analyzed the changes in inferior oblique muscle overaction and V-pattern strabismus and the frequency of limited elevation after surgery.

RESULTS

The record review identified 69 patients (138 eyes) who met inclusion criteria. V-pattern esotropia was present in 44 patients (64%) and V-pattern exotropia in 25 (36%). Full correction or undercorrection to <10(Δ) of V pattern was achieved in 82% of esotropia cases and 80% of exotropia cases. Response to surgery was influenced by the severity of the preoperative inferior oblique muscle overaction and the extent of the preoperative V pattern. The grading of the anterior transposition was not a significant independent predictor of surgical response. No patient suffered limitation of elevation postoperatively.

CONCLUSIONS

Anterior transposition of the inferior oblique muscles corrected V-pattern strabismus and reduced inferior oblique muscle overaction without creating limitation of elevation; however, it is unclear whether grading the transposition contribute to the success of the procedure.

Inferior oblique transposition onto the equator: the role of the equator in development of contralateral inferior oblique overaction

PURPOSE

To investigate the role of the location of the equator and orientation of newly attached inferior oblique (IO) muscle in the development of contralateral inferior oblique overaction (IOOA).

METHODS

Fourteen patients (14 eyes) with 5 to 12 prism diopters (PD) of hyperdeviation in primary position with unilateral, congenital, superior oblique palsy were included. Seven patients underwent modified IO transposition onto the equator (equator group) and seven patients underwent modified IO 14-mm recession (14-mm group). IOOA in the contralateral eye and the angle of strabismus were assessed at 3 months postoperatively.

RESULTS

Mean angles of hyperdeviation in primary gaze and sursoadduction were 0.7 and 2.1 PD in the equator group and 0.6 and 2.4 PD in the 14-mm group, respectively. Six patients (86%) developed anti-elevation syndrome and four patients (57%) showed definite 2+ or higher IOOA in the contralateral eye in the equator group. Three patients (43%) in the 14-mm group also developed contralateral IOOA, although it was 1+ or less. The postoperative difference in contra-lateral IOOA between groups was statistically significant (P = .04).

CONCLUSION

This finding suggests that vertical orientation of the IO muscle is another important contributor in the development of contralateral IOOA in addition to the location of the newly attached IO muscle.

Antielevation syndrome with onset of diplopia 10 years after inferior oblique anterior transposition

Antielevation syndrome as a complication of inferior oblique anterior transposition usually appears in the early postoperative period. A 29-year-old woman who had been operated on for right superior oblique palsy developed diplopia 10 years after surgery: motility examination was consistent with an antielevation syndrome. A right inferior oblique recession of 14 mm was performed on the previously transposed muscle; motility improved, and the patient has remained asymptomatic.

Anterior transposition of the inferior oblique muscle in the treatment of unilateral superior oblique palsy

PURPOSE

To determine whether unilateral inferior oblique anterior transposition alone could be an effective procedure for treating superior oblique palsy with inferior oblique overaction.

METHODS

The records of 38 patients who underwent unilateral inferior oblique anterior transposition for unilateral superior oblique palsy with inferior oblique overaction were evaluated. A comprehensive ocular examination including best-corrected visual acuity measurements, ductions, versions, and deviations at near and distance, head tilt test, abnormal head position, dilated fundus examination, and Titmus test was performed prior to and after surgery.

RESULTS

The mean patient age was 29 years, the mean follow-up was 32 months, the mean preoperative hypertropia in primary position was 14.29 ± 7.7 prism diopters (PD), and the mean inferior oblique overaction was 3.63 ± 0.67. Anterior transposition of the inferior oblique muscle was effective across a wide range of preoperative primary position hypertropia (4 to 35 PD) with a mean reduction in postoperative hypertropia of 12 PD. Inferior oblique overaction was reduced in all patients. No patient demonstrated postoperative primary position hypotropia. Surgery improved stereoacuity nearly two units using the Titmus stereoacuity scale.

CONCLUSION

Anterior transposition of the inferior oblique muscle is effective in correcting inferior oblique overaction and primary position hypertropia in the treatment of unilateral superior oblique palsy.

Anterior and nasal transposition of the inferior oblique muscle for dissociated vertical deviation associated with inferior oblique muscle overaction

PURPOSE

To determine outcomes after anterior and nasal transposition of the inferior oblique muscle for dissociated vertical deviation (DVD) associated with inferior oblique overaction.

METHODS

A total of 10 patients who had bilateral DVD with ipsilateral inferior oblique muscle overaction were included in this study. Patients underwent anterior and nasal transposition of the inferior oblique muscles to the medial edge of the inferior rectus muscle insertion; the horizontal rectus muscle was operated on for horizontal strabismus in 2 cases. The primary outcome variables were changes in DVD, inferior oblique muscle action, V pattern, and vertical deviation in primary and side gazes. Patients were evaluated 6 to 10 months (mean, 7.3 months) postoperatively for alignment and oculomotor examination.

RESULTS

Mean age at the time of surgery was 17.5 years. The average preoperative DVD for all eyes was 18.3(Delta) +/- 6.8(Delta), which decreased to 5.0(Delta) +/- 3.1(Delta) (p < 0.001) at 6 months. Mean inferior oblique muscle overaction decreased from +2.1 (range, +1 to +3) to +0.40 (range, -1 to 2). The mean preoperative V pattern was 24.9(Delta). After surgery, the mean correction of the V pattern was 14.8(Delta). Four patients developed 2(Delta) to 5(Delta) postoperative hypotropias in primary position at 6 months.

CONCLUSIONS

Anterior and nasal transposition of the inferior oblique muscle reduces DVD, V pattern, and inferior oblique muscle overaction with minimal complications.

Hang-back recession of inferior oblique muscle in V-pattern strabismus with inferior oblique overaction

INTRODUCTION

Although hang-back recession has widely been used as a weakening procedure on extraocular muscles, its effectiveness has mostly been studied for rectus muscles. We report a surgical technique for recessing the inferior oblique muscle and evaluate its effectiveness in V-pattern strabismus with inferior oblique overaction (IOOA).

METHODS

Fifteen patients with V-pattern strabismus and IOOA, 7 with V exotropia, and 8 with V esotropia underwent hang-back recession of inferior oblique muscle in addition to horizontal muscle surgery when required. The surgical technique consisted of free suspension of one or both inferior oblique muscles 10 mm along their physiological path using 6-0 polyglactin 910 sutures bridging the cut ends of muscle.

RESULTS

The mean preoperative V pattern in the V-exotropia group was 22(Delta) +/- 6(Delta) and 25(Delta) +/- 7(Delta) in V-esotropia group. The mean correction of V pattern after a mean follow-up period of 8 +/- 1 months was 19(Delta) +/- 2(Delta) for the V-exotropia group and 22(Delta) +/- 7(Delta) months for the V-esotropia group. Mean correction of IOOA in the V-exotropia group was 18(Delta) +/- 5(Delta); in the V-esotropia group, mean correction was 20(Delta) +/- 6(Delta) in the right eye and 18(Delta) +/- 2(Delta) in the left eye.

CONCLUSIONS

Hang-back recession of inferior oblique is another surgical procedure for correction of both V pattern and IOOA in V-pattern strabismus.

Inferior oblique muscle fixation to the orbital wall: a profound weakening procedure

INTRODUCTION

Recurrent or persistent inferior oblique overaction may occur after inferior oblique (IO) recession or anterior transposition. IO nasal and temporal myectomy and anterior-nasal transposition may result in undesirable IO palsy, exotropia, incyclotorsion, or limitation of elevation. Previous studies have shown that a rectus extraocular muscle may be profoundly weakened if the muscle insertion is reattached to adjacent orbital periosteum. We describe a reversible profound weakening surgical procedure of the IO muscle.

METHODS

A total of 10 consecutive subjects with V-pattern strabismus and/or IO overaction underwent IO orbital fixation procedure by attaching its insertion to the periosteum of the lateral orbital wall. One subject was not included because short follow-up. Five subjects with persistent IO overaction after IO anterior transposition underwent bilateral IO orbital wall fixation. Four subjects with no previous IO surgery underwent unilateral IO orbital wall fixation; 3 of these 4 subjects had superior oblique palsy with a large vertical deviation in primary position and 1 had a V pattern with asymmetric IO overaction.

RESULTS

V pattern significantly improved from 22(Delta) preoperatively to 7(Delta) postoperatively (p = 0.002). IO overaction improved from 2.5 (range, + 1.5 to + 4) to 0.1 (range, -2 to +3) postoperatively (p < 0.001). Six of 9 subjects had no residual overelevation in adduction postoperatively. Unilateral IO orbital fixation corrected 7(Delta) of vertical deviation in the primary position and 23(Delta) in adduction. Mean postoperative follow-up was 5 months.

CONCLUSIONS

IO orbital fixation has a profound weakening effect on the IO muscle. Advantages of this procedure include reversibility and that it can be converted into another form of weakening procedure, if required.

Antielevation syndrome after unilateral anteriorization of the inferior oblique muscle

PURPOSE

To report antielevation syndrome with restriction of elevation on abduction in the operated eye and overaction (OA) of the inferior oblique muscle (IO) of the contralateral eye after unilateral IO anteriorization (AT).

METHODS

Medical records were reviewed retrospectively in 8 of 24 patients who underwent unilateral IOAT. Four patients were referred from other hospitals after the same surgery.

RESULTS

Four patients had infantile esotropes. The rest showed accommodative esotropia, superior oblique palsy, exotropia, and consecutive exotropia. The mean amount of hyperdeviation was 16.3 PD (10 approximately 30). The mean restriction of elevation on abduction in the operated eye was -1.6 (-1 approximately -4) and IOOA of the contralateral eye was +2.7 (+2 approximately +3). IOAT of nonoperated eyes in 4 patients, IO weakening procedure of anteriorized eyes in 2 patients, and IO myectomy on an eye with IOAT in 1 patient were performed. Ocular motility was improved after surgery in all patients.

CONCLUSIONS

Unilateral IOAT may result in antielevation syndrome. Therefore bilateral IOAT is recommended to balance antielevation in both eyes. A meticulous caution is needed when performing unilateral IOAT.

Insertional pattern of the inferior oblique muscle

PURPOSE

We aimed to define the anatomy and anatomic variations of the inferior oblique muscle (IO) and classify its insertional pattern with photographs and drawings.

DESIGN

Cohort study.

METHODS

This study included 60 intact orbits of 30 (17 male and 13 female) embalmed adult cadavers. The inferior oblique muscle was dissected microanatomically from the origin to the insertion by using a dissection microscope. For each specimen, we photographed the insertional pattern of the muscle. A Vernier caliper was used to measure the width and length of the muscle at the insertion and from the division to the insertion, respectively.

RESULTS

We classified the inferior oblique muscle into four groups according to the insertional pattern. In the first group, the muscle was formed of only one belly ("single," five eyes, 8.3%). In the second group, the muscle had a main and a secondary belly ("double," 30 eyes, 50%). In the third group, the muscle had three bellies ("triple," 16 eyes, 26.6%). In the fourth group, the muscle had more than three bellies ("multiple," 9 eyes, 15%).

CONCLUSIONS

We found double, triple, and multiple muscle bellies in 91.7% of 60 cadaveric eyes. Ocular surgeons who do not frequently perform inferior oblique surgery should carefully examine the inferior temporal quadrant of the sclera to avoid missing portions of the inferior oblique muscle at the time of surgery.

Anterior and nasal transposition of the inferior oblique muscles

BACKGROUND

When performing anterior transposition of the inferior oblique (IO) muscle, placement of the posterior suture close to the lateral border of insertion of the inferior rectus (IR) muscle decreases the incidence of antielevation syndrome (AES). We hypothesized that placement of the suture nasal to the IR muscle insertion will convert the IO muscle into an intorter and depressor. Here we present the first series of results obtained with a new procedure for the treatment of elevation in adduction with extorsion and abnormal head postures.

METHODS

Twenty patients with IO muscle overaction, superior oblique (SO) muscle palsy, absent SO muscles, AES, or Duane syndrome were studied. Before surgery, each patient showed at least one, but often more, of the following signs: elevation in adduction, exotropia (XT) in up gaze, abnormal head posture, and extorsion. Each underwent anterior and nasal transposition (ANT) of the IO muscle, with the new insertion typically 2 mm nasal and 2 mm posterior to the nasal border of the IR muscle insertion.

RESULTS

Large improvements in ocular alignment, extorsion, and head posture were found in most patients. However, a poor result was noted in a patient with Y-pattern XT, who developed a mild amount of comitant XT after an extreme degree of ANT (4 mm nasal and 3 mm anterior to the nasal border of the IR muscle insertion). In Duane syndrome, ANT corrects upshoot, but downshoot may get worse. Mersilene permanent sutures, rather than dissolving suture materials, are recommended to avoid postoperative retraction of muscle fibers.

CONCLUSIONS

ANT converts the IO muscle into an intorter and tonic depressor and can significantly improve elevation in adduction. This procedure seems particularly useful in patients with severe or recurrent congenital and acquired SO palsies, particularly as a secondary procedure. Extreme ANT may induce exotropia in the primary position.