Oblique Muscle Tightening (Strengthening) Procedures
Tightening the inferior oblique muscle
As mentioned previously, the actual effect of strengthening procedures is tightening of the muscle. Inferior oblique muscle tightening is seldom performed. To be effective, advancement of the inferior oblique muscle requires reinsertion more posteriorly and superiorly, which is technically difficult and exposes the macula to possible injury.
Tightening the superior oblique muscle
Tucking, plication, advancement, and resection of the superior oblique tendon are discussed in Chapter 11. Tucking the superior oblique tendon enhances both its vertical and torsional effect. Just the anterior half of the superior oblique tendon may be advanced temporally and somewhat closer to the limbus, a procedure known as the Fells modification of the Harada-Ito procedure, to reduce extorsion in patients with superior oblique muscle paralysis.
Stay Sutures
A stay (pull-over) suture is a temporary suture that is attached to the sclera at the limbus or under a rectus muscle insertion, brought out through the eyelids, and secured to periocular skin over a bolster to fix the eye in a selected position during postoperative healing. Some surgeons believe that this technique is particularly useful in cases with severely restricted rotations. Its disadvantages are that patients experience some discomfort and that the limbal attachment of the stay suture tends to be lost before the desired interval of 10–14 days after placement.
Transposition Procedures
Transposition procedures involve redirection of the paths of the EOMs. In the treatment of paralytic strabismus, Duane retraction syndrome, and monocular elevation deficiency, these procedures utilize the 2 muscles adjacent to the abnormal muscle to provide a tonic force vector. Vertical deviations are a possible complication of vertical rectus muscle transposition surgery. The effect of the transposition can be augmented by resecting the transposed muscles or by employing offset posterior fixation sutures (Foster modification). It has recently been suggested that transposition of only the superior rectus muscle, combined with recession of the medial rectus muscle, can also be effective.
Foster RS. Vertical muscle transposition augmented with lateral fixation. J AAPOS. 1997;1(1):20–30.
Mehendale RA, Dagi LR, Wu C, Ledoux D, Johnston S, Hunter DG. Superior rectus transposition and medial rectus recession for Duane syndrome and sixth nerve palsy. Arch Ophthalmol. 2012;130(2):195–201.
Posterior Fixation
Posterior fixation is a procedure in which a rectus muscle is sutured to the sclera far posterior to its insertion. The effect is weakening of the muscle in its field of action while having little, if any, effect on the alignment in primary position. This is a particularly useful procedure for treatment of incomitant strabismus. A similar effect may be achieved, at least for medial rectus muscles, by fixation to the muscle pulley.
Complications of Strabismus Surgery
Diplopia
Diplopia can occur after strabismus surgery, occasionally in older children but more often in adults.
Surgery can move the fixated image out of a suppression scotoma. In the several months following surgery, various responses are possible:
Fusion of the 2 images may occur.
A new suppression scotoma may form, corresponding to the new angle of alignment. If the initial strabismus was acquired before age 10 years, the ability to suppress is generally well developed.
Diplopia may persist.
Prolonged postoperative diplopia is uncommon. However, if strabismus was first acquired in adulthood, diplopia that was symptomatic before surgery is likely to persist unless comitant alignment and fusion are regained. Prisms that compensate for the deviation may be helpful during the preoperative evaluation to assess the fusion potential and the risk of bothersome postoperative diplopia.
A patient with unequal visual acuity can frequently be taught to ignore the dimmer, more blurred image. Further treatment is indicated for patients whose symptomatic diplopia persists more than 4–6 weeks after surgery, especially if it is severe and in the primary position. If vision in the eyes is equal or nearly so, temporary prisms should be tried and, if necessary, oriented to correct both vertical and horizontal deviations. The prism power can be changed periodically to address any residual diplopia. If this approach fails, additional surgery or botulinum toxin injection is a consideration. In some cases, intractable diplopia can be controlled only by occluding or blurring the less-preferred eye with a MIN lens (Fresnel, Bloomington, MN), Bangerter foil (Ryser, St Gallen, Switzerland), or transluscent tape.
Kushner BJ. Intractable diplopia after strabismus surgery in adults. Arch Ophthalmol. 2002; 120(11):1498–1504.
Unsatisfactory Alignment
Unsatisfactory postoperative alignment—overcorrection, undercorrection, or development of an entirely new strabismus problem—is perhaps better characterized as one of several possible outcomes of strabismus surgery, albeit a disappointing one, rather than as a complication. Alignment in the immediate postoperative period, whether or not satisfactory, may not be permanent. Among the reasons for this unpredictability are poor fusion, poor vision, and contracture of scar tissue. Reoperations are often necessary.
Iatrogenic Brown Syndrome
Iatrogenic Brown syndrome can result from superior oblique muscle strengthening procedures. Taking care to avoid excessive tightening of the tendon when these procedures are performed minimizes the risk of this complication. When it occurs after superior oblique tucking, the tuck can sometimes be reversed if reoperation is undertaken soon after the original surgery. If not, then the standard superior oblique weakening procedures used in other forms of Brown syndrome can be employed (see Chapter 12).
Anti-Elevation Syndrome
Inferior oblique anteriorization can result in restricted elevation of the eye in abduction (antielevation syndrome). Reattaching the lateral corner of the muscle anterior to the spiral of Tillaux increases the risk; “bunching up” the insertion at the lateral border of the inferior rectus muscle may reduce the risk.
Kushner BJ. Restriction of elevation in abduction after inferior oblique anteriorization. J AAPOS. 1997;1(1):55–62.
Lost and Slipped Muscles
A rectus muscle that sustains trauma or that slips out of the sutures or instruments while unattached to the globe during an operation can become inaccessible posteriorly in the orbit. This consequence is most severe when it involves the medial rectus muscle, since it is the most difficult to recover. A lost muscle does not reattach to the globe but instead retracts through the Tenon capsule.
The surgeon should immediately attempt to find the lost muscle, if possible with the assistance of a surgeon experienced in this potentially complex surgery. Malleable retractors and a headlight are helpful. Minimal manipulation should be employed to bring into view the anatomical site through which the muscle and its sheath normally penetrate the Tenon capsule where, it is hoped, the distal end of the muscle can be observed and captured. If inspection does not reliably indicate that the muscle has been identified, sudden bradycardia when traction is exerted can often be confirmatory. Recovery of the medial rectus muscle has been achieved by using a transnasal endoscopic approach to the ethmoid sinus or by performing a medial orbitotomy. Transposition surgery may be required if the lost muscle is not found, but anterior segment ischemia may be a risk. Where to reattach the recovered muscle depends on several factors in the particular case and is largely a matter of judgment.
A slipped muscle is the result of inadequate suturing technique. The muscle recedes posteriorly within its capsule during the postoperative period. Clinically, the patient manifests a weakness of that muscle, with limited rotations and possibly decreased saccades in its field of action (Fig 14-1). Surgery should be performed as soon as possible in order to secure the muscle before further retraction and contracture take place. The surgeon can prevent slippage by making full-thickness locking bites that include muscle tissue, not merely capsule, before disinsertion. In reoperations for strabismus with deficient rotations, slippage or “stretched scar” should be suspected and the involved muscles explored.
Figure 14-1 Slipped left medial rectus muscle. Left, Gaze right shows inability to adduct left eye. Center, Exotropia in primary position. Right, Gaze left shows full abduction. Note left palpebral fissure is wider than right.
Pulled-in-Two Syndrome
Dehiscence of a muscle during surgery has been termed pulled-in-two syndrome (PITS). The dehiscence usually occurs at the tendon–muscle junction, and the inferior rectus may be the most frequently affected muscle. Advanced age, various myopathies, previous surgery, trauma, or infiltrative disease may predispose a muscle to PITS by weakening its structural integrity. Treatment is, when possible, re-anastomosis of the muscle using techniques similar to those employed for lost muscles (see previous section).
Perforation of the Sclera
During reattachment of an EOM, a needle may penetrate the sclera and pass into the suprachoroidal space or perforate the choroid and retina. Perforation can lead to retinal detachment or
endophthalmitis (see BCSC Section 9, Intraocular Inflammation and Uveitis); in most cases, it results in only a small chorioretinal scar, with no effect on vision. Most perforations are unrecognized unless specifically looked for by ophthalmoscopy. If vitreous escapes through the perforation site, many surgeons apply immediate local cryotherapy or laser therapy. Topical antibiotics are generally given during the immediate postoperative period, even when vitreous has not escaped. Ophthalmoscopy during the postoperative period is an appropriate precaution, with referral to a retina consultant as needed.
Postoperative Infections
Intraocular infection is uncommon following strabismus surgery. Some patients develop mild conjunctivitis, which may be caused by allergy to suture material or postoperative medications, as well as by infectious agents. Preseptal and orbital cellulitis with proptosis, eyelid swelling, chemosis, and fever are rare (Fig 14-2). These conditions usually develop 2–3 days after surgery and generally respond well to systemic antibiotics. Patients should be warned of the signs and symptoms of orbital cellulitis and endophthalmitis so they will seek emergency consultation if necessary.
Figure 14-2 Orbital cellulitis, right eye, 2 days after bilateral recession of the lateral rectus muscles.
Foreign-Body Granuloma and Allergic Reaction
A foreign-body granuloma occasionally develops after EOM surgery, usually at the muscle’s reattachment site. The granuloma is characterized by a localized, elevated, hyperemic, slightly tender mass (Fig 14-3). It may respond to topical corticosteroids. Surgical excision is necessary if the granuloma persists. Reactions to suture materials are now infrequent because gut suture is rarely used (Fig 14-4).
Figure 14-3 Severe postoperative granuloma over the right medial rectus muscle persisting 1 year after medial rectus recessions.