Inferior Oblique Surgeries

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There are many types of inferior oblique surgeries that are commonly performed by strabismologists. The anatomy of inferior oblique muscle is complex, however, indications and contraindications of inferior oblique surgery should be identified and treated surgically.

Disease Entity

Strabismus/ocular misalignment


Inferior oblique surgery is a common procedure performed along with other strabismus surgeries or as an isolated surgery. Weakening procedures are more commonly performed than the strengthening procedures.

Anatomy & function of the inferior oblique

The inferior oblique is the shortest extraocular muscle measuring 37mm and has a very small tendon (1-2 mm). It arises from the orbital surface of the maxilla and inserts on the posterior inferolateral aspect of the eyeball under the lateral rectus muscle[1]. It is innervated by the inferior division of the oculomotor nerve (IIIrd nerve) and the blood supply is by the infraorbital artery. It is an elevator, abductor, and extorter[2].

Inferior oblique overaction

Inferior oblique overaction (IOOA) manifests as overelevation in adduction and is usually associated with horizontal deviations. The cause can be primary or secondary. Primary IOOA is most commonly associated with infantile esotropia, accommodative esotropia, and intermittent exotropia and the etiology remains unknown[3]. Secondary reasons include superior oblique palsy. Surgical methods to weaken the inferior oblique include myectomy, myotomy, tenectomy, recession, anterior transposition, antero-nasal transposition, and denervation-extirpation. Inferior oblique underaction is seen in Brown’s syndrome and inferior oblique palsy[4]. Strengthening techniques have been tried on the inferior oblique muscle, however they do not yield good results since the IO lacks a tendinous portion.

Indications for weakening inferior oblique

1. V-pattern strabismus with inferior oblique overaction (infantile esotropia, accommodative esotropia, intermittent exotropia)[5]

2. Primary inferior oblique overaction

3. Dissociated vertical deviation

4. Superior oblique palsy

5. Duanes Retraction syndrome with inferior oblique overaction

6. Excyclotorsion.

Contraindications for inferior oblique muscle surgery

1. V-pattern strabismus without IOOA[6]

2. X-pattern strabismus

3. Craniofacial syndromes with apparent IOOA.

Surgical techniques

First, the globe is retracted in the superonasal quadrant. Most strabismus surgeons make an incision in the inferotemporal quadrant 8mm from the limbus in the bulbar conjunctiva and intermuscular septum[7]. A perpendicular incision is made in the tenon’s fascia to expose the bare sclera. Under direct visualization, a muscle hook is placed below the belly of the muscle and the IO is hooked. The muscle is freed of all the attachments avoiding injury to the inferotemporal vortex vein. The muscle is disinserted close to the insertion and 6-0 polyglactin sutures are passed just posterior to the clamp[8]. The muscle is then re-attached at the desired point and the conjunctiva is closed using 8-0 polyglactin sutures.

Fornix incision in the inferotemporal quadrant
Hooking of the inferior oblique muscle
Partial thickness scleral bite at a desired point for IO recession


Myotomy is a self-adjusting procedure in which the muscle is incised close to the insertion and allowed to retract without placing any sutures. The result of this procedure is unpredictable since if the muscle has more overaction then it may contract more as compared to a muscle that has less overaction[9].


This is also a self-adjusting procedure in which 2 clamps are placed, one close to the insertion and the other 4 to 8 mm from the first clamp[4]. The muscle is excised between the clamps and the ends are cauterized to prevent bleeding. Reoperations may be difficult as it is not easy to relocate the muscle.


In this technique, the muscle is receded and reattached to the sclera along its course at a desired point[10]. The various points of attachment are listed below.

Park’s recession technique – For a 10 mm recession, the anterior end of the IO is attached 2 mm lateral and 3 mm posterior to the lateral end of the inferior rectus insertion, and the posterior end is 5 mm posterior.

Fink’s recession technique – For an 8 mm recession, the anterior point is 6 mm inferior and 6 mm posterior to the inferior edge of the lateral rectus insertion and the posterior point is 5-6 mm posterior to the anterior point. For a 10 mm recession, the IO is inserted 8mm posterior and 2 mm inferior to the lateral rectus insertion.

Elliot and Nankin’s recession technique – The anterior end of IO is inserted at the lateral end of the inferior rectus insertion and the posterior end is 5 mm posterior.

Graded recession – Some ophthalmologists recommend graded measurements according to the amount of recession required[11].

Recommendations for graded recession

Anterior Transpositioning

In pure antero-transpositioning, the IO is placed just below the anterior border of the lateral rectus muscle. Most strabismus surgeons use the anterior border of the inferior rectus as the reference for anteriorization and the IO is inserted at the level of the inferior rectus (zero station).

Anterior Transpositioning

Total anteropositioning

In this procedure, the IO muscle is re-inserted anterior to the inferior rectus. This weakens the elevator action and converts the muscle into a depressor. This surgery is performed for dissociated vertical deviation with IOOA[12].

Total anteropositioning

Anterior Nasal Transpositioning

In Anterior and Nasal Transposition (ANT) of the IO muscle, the new insertion is 2 mm nasal and 2 mm posterior to the nasal border of the IR muscle insertion. ANT converts the IO muscle into an intorter and depressor and improves elevation in adduction. This procedure is useful in patients with severe or recurrent congenital and acquired superior oblique palsies, especially when performing a secondary procedure[13].

Anterior Nasal Transpositioning

Nasal Myectomy

Nasal myectomy is found to be effective in cases with residual IOOA even after anteriorization has been performed. The IO is hooked at the anteriorized end and dissected along its course to the nasal end. Two muscle clamps are placed 5 mm apart. The muscle tissue is resected between the clamps, ends are cauterized before being released. The temporal portion of the IO then acts as the new origin of the muscle since the neurovascular bundle is present here[14].


Complications can occur following inferior oblique recession. These include undercorrection, overcorrection, hemorrhage, pupil dilation and fat adherence syndrome[15].

Under correction & Overcorrection

When an overcorrection occurs, the eye depresses on adduction and an A-pattern becomes evident. An anteriorization can be converted to a recession and if a secondary superior oblique overaction develops, a tenotomy of the superior oblique can be performed. Under corrections are more common than overcorrections. If an anterotranspositioning was performed as the first procedure, a nasal myectomy can be effective in reducing the IOOA.


Since the IO is a highly vascularized muscle, it can bleed profusely during surgery. Blood can go subconjunctival and even beneath the eyelid to cause ecchymosis. Optic atrophy can occur if hemorrhage occurs near the optic nerve region. Perforation of the vortex vein can also lead to bleeding.

Pupil dilation

Excessive trauma to the IO can cause pupillary dilation as a result of damage to the nerve to the ciliary ganglion that bears the parasympathetic fibers to the pupil. Mydriasis can be temporary or permanent. Permanent mydriasis may also be a result of hemorrhage in the optic nerve region.

Fat adherence syndrome

Rupture of the posterior tenon’s can lead to prolapse of adipose tissue in the inferotemporal quadrant.


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