Adjustable-Suture Strabismus Surgery
Monica S. Zhang
Scott R. Lambert
Strabismus, a misalignment of the eyes that can occur at any age, is a complex ocular condition that may be caused by one or more mechanical, neurological, genetic, or idiopathic factors. Strabismus surgery attempts to correct or compensate for these factors by changing the mechanical forces. In children, strabismus may lead to loss of depth perception and amblyopia. Adults with strabismus will often develop diplopia, abnormal head posturing, and impaired stereopsis, which in turn may impair activities of daily living and quality of life.1,2 Strabismus surgery in adults has been shown to be beneficial in improving diplopia, binocular fusion, and psychosocial functioning in addition to being cost-effective, with a health value similar to that of cataract surgery.2,3,4,5,6 However, even the simplest of strabismus surgeries can yield unpredictable results—a similar surgery for equal deviations in two patients can yield different results.7 Due to the number of variables and our lack of understanding of these variables for a given patient, it is not surprising that it is difficult to accurately predict the effect of a given extraocular muscle procedure on the long-term ocular alignment.
Adjustable-suture strabismus surgery arose as a means to improve strabismus surgery outcomes. The earliest approaches to repositioning or adjusting a muscle were not well accepted due to the complexity of the techniques and to a lack of patient tolerance. In 1975, Jampolsky described a two-stage adjustable technique that offered a method for assessing the effects of strabismus surgery on conscious patients that was easy to perform and well tolerated: Ocular muscle repositioning is performed first under general anesthesia, and adjustment of the ocular position under local anesthesia is performed later.8
In the time since Jampolsky popularized this procedure, various studies have been done to evaluate the success of the adjustable technique; however, there is a lack of consensus regarding whether the technique results in better outcomes than traditional strabismus surgery. A recent Cochrane survey did not find evidence supporting the use of adjustable sutures when performing strabismus surgery.9
No randomized prospective studies have been performed for adjustable-suture surgery, and thus far, most of the retrospective studies conducted on the subject have focused more on short-term outcomes of adjustable-suture surgery.10
Adjustable sutures can be used on almost all strabismus patients who undergo rectus muscle surgery, and more recently, have been increasingly used in children. Most strabismus surgeons, however, limit their use of the procedure because of the additional time required, the complexity of the procedure, the need for patient cooperation, patient discomfort, the effect of postoperative drift, and the lack of evidence of a significant benefit for the routine strabismus patient. Although the Cochrane survey results did not definitively establish the efficacy of adjustable-suture use, recent studies have established improved outcomes following the use of adjustable-suture use overall and in specific clinical contexts. The most commonly accepted indications for adjustable-suture techniques include complex strabismus conditions with less predictable outcomes, strabismus with unknown or unexpected findings at surgery, and strabismus where precise alignment is critical for the elimination of symptoms. Strabismus with less predictable surgical outcomes includes paretic or restrictive strabismus, previously operated strabismus, very large-angle strabismus, and long-standing strabismus with contracture of the extraocular muscles.
The majority of the studies done on patients with thyroid eye disease suggest that adjustable sutures improved outcomes.11,12,13 Lueder et al.12 conducted one of the studies with a longer follow-up time of 41 months and found that of the 47 patients who had an adjustable-suture procedure, 47% of those patients had resolution of their diplopia in both primary and reading positions that did not require the use of prisms. Kraus and Bullock similarly found improved success with the use of adjustable suture 64% versus 38% in the nonadjustable group, with particular benefit for vertical deviations, although their numbers did not reach statistical significance and their inclusion criteria were rather strict.13 A more recent study found similar success rates for the adjustable and non-adjustable groups.10 The variability of the results in these studies can partly be attributed to the nuances in the definition of a “successful” outcome. Furthermore, the combination of the restrictive effect of thyroid eye disease, postoperative changes from inflammation, and potential for disease flare further reduce the precision with which muscle placement is achieved. Nassar et al.14 noted in their study of 50 patients with Graves’ ophthalmopathy that relative symmetry of orbitopathy at onset and a shorter time between onset of thyroid eye disease and surgery predict better outcomes. Although they did not focus on the use of adjustable suture, their results reinforce the idea that adjustable sutures would aid in a situation where there is asymmetry. It has also been shown that a shorter duration of constant ocular misalignment and the capacity for ocular fusion are positive predictors for restoration of macular binocular vision for those adults with acquired strabismus.15
Studies have not been performed to look specifically at the benefit of adjustable suture use in cases of slipped muscles, trauma or congenital disorders, such as Duane syndrome, Brown syndrome, and congenital fibrosis. However, many authors suggest that patients with these etiologies of strabismus tend to anecdotally benefit from the use of adjustable sutures as they represent cases of complex strabismus where intraoperative findings and postoperative results are less predictable.8,16,17 Patients experiencing vertical strabismus secondary to local anesthetic myotoxicity have a good outcome in alignment, with recovery of fusion, when a large recession on an adjustable suture is done.18
Patients with extremely small or large eyes, aberrant oculomotor innervation, combined horizontal, vertical, and cyclotorsional deviations, or who are undergoing unconventional strabismus procedures are more likely to experience an unpredictable outcome and may benefit from the use of adjustable sutures. When analyzing the utility of adjustable sutures for specific type of deviations, their use seems to be most beneficial in exotropias and vertical deviations. Keech and Heckert17 showed that in 51 procedures performed with adjustable sutures for acquired vertical deviations, 78% were successful, particularly for surgeries where only recti muscles were moved. Keech et al.19 looked at 333 patients who had undergone strabismus surgery with adjustable suture over a 10-year period and found that vertical and complex deviations were better suited for the use of adjustable sutures, whereas complex cases with restriction or paresis were more unpredictable. A retrospective study done by Currie et al.20 on surgical correction using adjustable sutures for large-angle exotropia in 26 adults had a success rate of 77%. A more recent study done by Mireskandari et al.21 confirmed the improved success rate when adjustable sutures were used for exotropias, 80.8% versus 65.9%, and demonstrated a trend toward improved alignment in vertical deviations.
Studies have also suggested that primary operations using adjustable sutures tend to be more successful than reoperations in specific subsets of patients. Keech and Heckert17 showed that for an acquired vertical deviation, patients undergoing a primary procedure using adjustable sutures had a success rate of 81%, whereas patients undergoing reoperations had a success rate of 71%. However, the difference was not statistically significant. Weston et al.22 described greater success rates for patients with esotropia or exotropia undergoing primary surgeries (88% for both groups) as compared with those undergoing reoperations (81% and 74%, respectively). Similarly, the patient group studied by Mireskandari et al. had better outcomes that were statistically significant for primary exotropia surgery. However, adjustable sutures have also been shown to result in improved alignment in patients undergoing a reoperation, specifically in adult patients with childhood strabismus.10 The overall lower success rate in reoperations with both the traditional and adjustable-suture techniques is not surprising and can be attributed to multiple factors, including postoperative adhesions and a patient population whose strabismus tends to be more complex and therefore have deviations that are not easily fixed with the usual surgical nomograms.23,24 These studies all suggest that the use of adjustable sutures ought to be considered in each strabismus patient that is cooperative and willing to undergo the adjustment procedure, rather than only giving consideration to those undergoing strabismus surgery for a reoperation or complicated strabismus.
ADJUSTABLE-SUTURE USE IN CHILDREN
It was previously thought that children (below the age of 10) would not be ideal candidates for the adjustable-suture technique due to the lack of cooperation and the risk associated with additional anesthetic use. However, recent studies and newer techniques suggest that adjustable sutures can lead to a successful outcome in this population with success rates ranging from 74% to 88%.25,26,27 Awadein et al.28 conducted a retrospective study of 396 children, 10 years old or younger, who underwent horizontal eye muscle surgery with either an adjustable-suture or non-adjustable technique and who were then adjusted under topical proparacaine or IV propofol anesthesia. Success rates were higher overall for the adjustable group, 79%, compared with the nonadjustable group, 64%. Furthermore, adjustable sutures used in the correction of esotropias had a higher success rate that was statistically significant; the success rate for adjustable sutures used for exotropias trended toward higher success. Interestingly, the improved benefit for esotropia correction using adjustable sutures in children is opposite of what is typically found in adults—that exotropias have better outcomes. A major disadvantage to the adjustable-suture technique in children is the extra time and personnel needed for the various components of the surgery.
There are no absolute contraindications for adjustable-suture techniques in strabismus surgery. It is, however, unwise to attempt the procedure on patients who are unable to cooperate with the adjustment.
Patients can develop bradycardia at the time of the adjustment as a result of the oculocardiac reflex. This may pose a slight risk to patients with heart disease, although no adverse outcomes have been reported as a result of this complication.
Adjustable-suture techniques should be attempted only by ophthalmologists with considerable experience in examining and operating on strabismus patients. A thorough preoperative evaluation must be performed. Adjustable sutures usually cannot correct a poor surgical outcome resulting from an incomplete or inaccurate examination. Adjustable sutures are also more likely to aggravate rather than correct surgical problems resulting from inexperience. Poor surgical techniques with excessive tissue swelling or hemorrhage can make the adjustment difficult or impossible to perform and result in the need for additional surgery. The surgeon should have a good appreciation of the extraocular muscle actions and be familiar with the methods for managing oculomotor incomitancy. For example, very large recessions with adjustable sutures should be avoided in concomitant strabismus, since this only allows for the adjustment in one direction. A better choice would be to operate on an additional muscle and allow the adjusted muscle to be recessed less. In this case, the surgeon has the option of recessing or advancing the adjusted muscle depending upon the alignment.
The surgeon should exclude patients who are unlikely to tolerate this procedure. A brief discussion with a patient will usually reveal those who are unable or unwilling to cooperate for the postoperative adjustment. The ability to tolerate forced duction testing or a cotton applicator applied to the conjunctiva after administering a topical anesthetic are reliable methods for assessing a patient’s suitability for adjustable-suture surgery. Prior to surgery, the patient’s anxiety can be relieved and cooperation enhanced by describing the procedure and the adjustment, including the expected level of postoperative discomfort.
Determination of fusion potential prior to surgery using the Titmus fly test, Randot stereoacuity test, or the Worth 4-dot test in those without stereopsis can aid in surgical planning, in determining which patients will likely be able to sustain optimal alignment postoperatively and in illustrating the potential binocular vision that they may achieve after surgery. Careful preoperative deviations should be obtained. Forced ductions may help in determining whether any limitations of duction are secondary to the restriction of the antagonist or to paresis of the agonist muscle. Laboratory and imaging tests may be helpful in cases where the etiology of the strabismus may be systemic, such as myasthenia gravis or an acute cranial nerve palsy in the setting of hypertension or diabetes.
Adjustable-suture strabismus surgery may be performed using topical, local, or general anesthesia. Topical or local anesthesia can be used for patients whose medical comorbidities may preclude them from receiving general anesthesia. Topical anesthesia works best with very cooperative patients who require minimal operating time and little manipulation of the muscles. Multiple muscles or strabismus reoperations are poor cases for this approach. Good choices for topical anesthesia include proparacaine (0.5%), lidocaine solution (4%), tetracaine (0.5%), or bupivacaine (0.5%). An advantage of topical anesthesia is that a measurement of the ocular alignment and adjustment of the muscle can be performed at the time of the operation; however, patients may experience greater discomfort with muscle traction.29,30,31
Local or regional anesthesia in the form of a retrobulbar, peribulbar, or subconjunctival injection of mepivacaine (2%) or lidocaine (2%) is routinely used by some strabismus surgeons in cooperative patients.32 Shortacting agents are preferred when administering local anesthesia, as it requires 4 to 6 hours for the extraocular muscles to recover sufficiently to perform an accurate adjustment.33 Longer-acting agents such as bupivacaine prolong the muscle paralysis and delay the time to adjustment and may preclude same-day adjustment. The addition of hyaluronidase to 2% mepivacaine has been found to decrease the duration of the anesthetic and allow for faster recovery of extraocular muscle function.32 Sub-Tenon infusion is another method of delivering regional anesthesia, as the conjunctiva has to be opened for surgery and allows for more direct deposition of the agent while avoiding inadvertent injection of the muscle.34