Strabismus with unpredictable surgical outcome includes paretic or restrictive strabismus, previously operated strabismus, large-angle strabismus, and longstanding strabismus with contracture of the extraocular muscles. Ocular motor palsies, thyroid related strabismus, and strabismus secondary to orbital fractures would be included in this category. Other possible conditions include congenital disorders such as Duane's syndrome, Brown's syndrome, and congenital fibrosis. Finally, patients with extremely small or large eyes, aberrant oculomotor innervation, combined horizontal and vertical deviations, or those undergoing unconventional strabismus procedures are more likely to benefit from adjustable sutures.

Strabismus with unknown or unexpected findings at surgery makes the outcome less predictable and offers a good indication for the use of adjustable sutures. This situation may occur from trauma to the orbit or after cataract surgery, retinal reattachment surgery, or prior strabismus surgery.

Patients who develop strabismus after childhood often have good potential for single binocular vision if the eyes are precisely aligned. Small overcorrections or undercorrections commonly result in troublesome diplopia in these cases. The adjustable suture technique provides an opportunity for the surgeon to “fine tune” the ocular alignment in these patients.

Patients can develop bradycardia at the time of the adjustment as a result of the oculocardiac reflex.^6,7 This may pose a slight risk to patients with heart disease. Currently, no problems 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 suture techniques usually cannot correct a poor surgical outcome resulting from an incomplete or inaccurate examination. Adjustable sutures also are more likely to aggravate rather than correct surgical errors 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. It is especially important when using adjustable sutures to understand the most likely changes in the ocular alignment in the immediate postoperative period and consequently the most desirable initial postoperative alignment for each type of strabismus.

PREOPERATIVE PREPARATION

The surgeon should exclude patients who are unlikely to tolerate this procedure. A brief discussion with a patient usually reveals those who are unable or unmotivated to cooperate for the postoperative adjustment. Diagnostic tests may be helpful in questionable cases. The ability to tolerate applanation tonometry, forced duction testing, or a cotton applicator applied to the conjunctiva after administering a topical anesthetic have been recommended as methods for assessing a patient's suitability for adjustable suture surgery.⁸ Before 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.

ANESTHESIA

Adjustable suture strabismus surgery may be performed using topical, local, or general anesthesia. Topical anesthesia works best with cooperative patients in whom minimal manipulation of the muscle is required. I prefer proparacaine (0.5%) or lidocaine solution (4%), although tetracaine (0.5%) or cocaine (5% to 10%) also are effective. An advantage of topical anesthesia compared with other methods of anesthesia is that a measurement of the ocular alignment and adjustment of the muscle can be performed at the time of the operation.^9,10 Local or regional anesthesia in the form of a retrobulbar, peribulbar, or subconjunctival injection of mepivacaine (2%) or lidocaine (2%) is used routinely by some strabismus surgeons in cooperative patients.^11,12 After administering local anesthesia, it requires 4 to 6 hours for the extraocular muscles to recover sufficiently to perform an accurate adjustment.¹³ General anesthesia also is commonly used for strabismus surgery, especially in bilateral procedures and procedures where extensive manipulation of the muscle is necessary. General anesthetics that provide for rapid recovery of consciousness are preferred for adjustable suture strabismus surgery. Intravenous propofol in combination with nitrous oxide has been shown to be an effective general anesthetic agent that allows for faster recovery from strabismus surgery.^14,15 Muscle-relaxing agents that act by depolarizing the neuromuscular junction (e.g., succinylcholine) may have a prolonged affect on muscle tone and should be avoided during general anesthesia. Nondepolarizing muscle relaxants do not appear to be a hindrance in adjustable suture strabismus surgery.¹⁵ Regardless of whether topical, local, or general anesthesia is used, preoperative analgesics or hypnotics should be avoided, as should all intraoperative or postoperative drugs that might alter the patient's level of consciousness at the time of the adjustment.

The method for preparing the eye and ocular adnexa before surgery is the same as for any strabismus operation. A generous area of the lower lid and lateral canthal skin should also be cleaned with 5% povidone iodine solution. This allows the adjustable sutures to be taped to the skin after surgery.

SURGICAL TECHNIQUE

A variety of adjustable suture techniques have been developed for strabismus surgery. The procedure described here is easy to perform and may be best suited for the surgeon who is not experienced in using adjustable sutures. This technique is similar to nonadjustable suture surgery and requires a minimal amount of manipulation during the adjustment.

A standard limbal conjunctival approach is most commonly used with adjustable suture surgery. Relaxing incisions at the superior and inferior margin of the peritomy provide good access to the muscle. The relaxing incisions should be kept relatively parallel to allow for a conjunctival recession.

For a rectus muscle recession, the muscle is cleaned of the attachments of anterior tenon's capsule and intermuscular septum in the same manner as for nonadjustable strabismus surgery. The muscle attachments must be cleaned sufficiently to allow for movement during the adjustment. Tissue manipulation is minimized to reduce the postoperative swelling and prevent excessive bleeding, which may hinder the adjustment. A double-armed 6-0 polygalactin suture with spatulated needles (S-24 or TG 100-8) is placed in the muscle tendon 0.5 mm from the insertion with full-thickness lock bites at each edge. Each lock bite incorporates one fourth to one third of the width of the muscle tendon to aid hemostasis and provide a secure muscle attachment during the adjustment (Fig. 1). After the muscle is disinserted, each arm of the suture is passed through a scleral tunnel at the muscle insertion. The tunnels are 4 to 6 mm in length and are placed through half-thickness sclera at a 45° to 60° angle from the insertion. The needles exit the sclera just anterior to the insertion 1 to 2 mm apart (Fig. 2). It is important to carefully clean the episclera and cauterize blood vessels near the scleral tunnels to reduce the chance of suture drag and hemorrhage during the adjustment.

After the needles are removed, the suture ends are tied together loosely with a double throw. The eye is rotated away from the recessed muscle (i.e., laterally if the medial rectus muscle is adjusted) to allow the muscle to retract posteriorly beyond the intended position of recession. A mark is placed on the sclera with Castroviejo calipers preset to the desired amount of the recession from the original muscle insertion. The double throw is tightened until the muscle is pulled up to the scleral mark and the poles of the muscle are equal distance from the insertion. A loop or slip knot is placed over the double throw to secure the suture (Fig. 3). The conjunctiva is closed with 7-0 chromic suture. The conjunctival flap is pulled up until it partially covers the adjustable knot. The relaxing incisions may be closed with additional sutures if necessary (Fig. 4). The ends of the adjustable suture are taped to the skin of the lower lid or tucked into the lower cul-de-sac and held in place with an antibiotic-steroid ointment. An eye patch helps to keep the sutures in place during the immediate postoperative period.

MODIFICATIONS OF THE ADJUSTABLE TECHNIQUE

Since the introduction of the modern adjustable suture technique, several modifications have been described that offer some advantages. Although usually performed on muscles that are recessed, adjustable sutures also can be used with resected muscles. Most surgeons suggest resecting 1 to 2 mm more than is thought to be required for optimal ocular alignment. This allows for an advancement or recession of the muscle as necessary during the adjustment. For small resections, the single double-armed suture technique used with a muscle recession is acceptable. For larger resections with excessive tension on the muscle, a two-suture technique probably is best (Fig. 5). Both sutures should be adjusted equally if the two-suture technique is used.

Many strabismus surgeons prefer to use a sliding adjustable knot instead of the slip knot. They believe that the sliding knot is easier to adjust, provides a more accurate assessment of the amount of the adjustment, and improves the chances that the suture ends will be pulled up an equal amount. Disadvantages of the sliding knot are that the procedure is more difficult to perform and leaves a bulkier knot, which increases the chances of postoperative irritation.¹⁶ The sliding adjustable suture uses the same muscle exposure and suturing methods as previously described. The scleral tunnels also are prepared in the same way as for the adjustable loop suture except that the needles exit the scleral as close to one another as possible. After the sutures have been brought through the tunnels, one suture end approximately 10 cm long is cut off and used to make the sliding knot. The muscle is pulled up and held at the insertion by the sutures. The suture end is tied around both muscle sutures near their exit from the sclera as tightly as possible using three single throws (Fig. 6). One or both ends of the sliding suture are left long for grasping during the adjustment. The sliding suture is moved back and forth on the muscle sutures several times to ensure that it will slide easily during the adjustment. The recession is obtained by pulling the muscle up to the muscle insertion and measuring the desired distance anteriorly from the scleral exit site along the muscle suture. The sliding suture is placed at this position, and the muscle is allowed to retract (Fig. 7). Variations in the conjunctival incision and closure have been described.^17,18 Complete closure of a limbal conjunctiva incision can be delayed until after the adjustment. One corner of the conjunctival flap is closed at surgery while the other corner either is left free or loosely attached with a loop of suture. After the adjustment, the loop is cut and the suture ends tied tightly together (Fig. 8). The conjunctival cul-de-sac incision popularized by Parks also can be used during adjustable suture surgery.^19,20 An adjustable loop knot or a sliding knot may be used with the cul-de-sac technique (Fig. 9). After the scleral tunnels have been made, one of the needles is removed, and the two suture ends are tied together with a square knot. The conjunctiva and tenon's capsule are repositioned. Using the remaining needle to make a small conjunctival puncture, the square knot is passed through the conjunctiva at a point where it lies directly over the muscle insertion. An adjustable sliding or loop knot is placed over the conjunctiva. The cul-de-sac incision may or may not be closed at the time of surgery, depending on the size of the wound and the surgeon's preference. After the adjustment is completed, the adjustable suture knot is covered with conjunctiva. This is accomplished by lifting the conjunctiva on each side of the small opening created by the sutures and allowing the adjustable suture knot to fall back through the previous puncture site. An alternate method is to adjust the suture directly through the conjunctival cul-de-sac incision. A traction suture is placed near the pole of the muscle insertion to allow for retraction of the conjunctiva.²¹ After the adjustment is completed, the traction suture is removed and the conjunctiva stroked back into its normal position without suturing.

It can be difficult to accurately determine how much the muscle was moved during the adjustment. One approach to this problem is to tie an extra piece of suture around one or both ends of the adjustable suture at a predetermined distance from the scleral tunnels. The sliding adjustable knot works best with this technique. This measuring or marking suture is a reference point for determining the amount of adjustment. The suture is removed after the adjustment is completed.²²

Another useful modification of the adjustable suture technique is to use a scleral traction suture. The traction suture reduces the chance of pain and hemorrhage during the adjustment by providing a handle to stabilize the eye. The suture is placed as a moderately deep scleral bite, 2 to 4 mm from the limbus, and tied in a loose loop. It is best to place the traction suture inferior and anterior to the muscle insertion for horizontal muscles and temporal and anterior to the muscle insertion for vertical muscles (see Fig. 4). The ideal suture for adjustable strabismus surgery is absorbable and strong, ties securely, and offers minimal tissue resistance.²³ Most strabismus surgeons use 6-0 synthetic absorbable suture made of polyglactin 910 or polyglycolic acid. Either suture can be used for all of the adjustable techniques and modifications. Spatulated needles are preferred by most surgeons for adjustable suture surgery. The conjunctiva also can be closed with the same suture but a more rapidly absorbing suture (i.e., 6-0 or 7-0 plain gut or chromic gut) is tolerated better by most patients.

Adjustable suture strabismus surgery is almost exclusively restricted to rectus muscles. Suture adjustment is difficult on the oblique muscles because of the posterior orientation of the muscle insertion. A technique for tucking the superior oblique tendon that provides a limited postoperative adjustment has been described.²⁴ An adjustable suture approach to the anterior fibers of the superior oblique tendon for the treatment of excyclotorsion also has been developed.²⁵

TIMING

Excessive swelling of the eyelids or conjunctiva hinders the adjustment of extraocular muscles. Immediately after strabismus surgery, the patient's head should be elevated and ice applied to the eye and periorbital tissues. If the patient had strabismus surgery under topical anesthesia, the adjustment may be performed in the operating room during or immediately after the operation. After general anesthesia, the adjustment can be performed as soon as the patient is alert and responsive. Adjustments are easier if performed within 18 to 24 hours after surgery, although delays as long as 1 week after surgery have been reported.²⁶ I generally perform strabismus surgery using adjustable sutures early in the morning and adjust the muscle or muscles on the afternoon of surgery or, occasionally, the following morning. If surgery is performed using retrobulbar or peribulbar lidocaine, the adjustment should be delayed 4 to 6 hours for the effects of the anesthetic to wear off.¹³

LOCATION AND EQUIPMENT

I perform postoperative muscle adjustments in a fully equipped eye examination lane, although it also can be done at the bedside. A good overhead spot light and equipment for measuring ocular alignment must be available. The surgical instruments necessary to perform the adjustment should be kept in sterile, prepared packages (Fig. 10). A topical anesthetic should be available for the adjustment, as well as a topical antibiotic or antibiotic-steroid ointment after the adjustment is completed. An assistant is helpful for holding the eyelids open and stabilizing the globe.

The adjustment is performed with the patient in the supine position to minimize any symptoms from a vasovagal reaction. After each adjustment, the patient is placed in a sitting position and the ocular alignment assessed.

TECHNIQUE

Topical anesthetic is applied to both eyes before the postoperative examination. A cotton-tipped applicator soaked in the topical anesthetic and applied to the area of the adjustable suture provides additional anesthesia. Proparacaine is effective in most cases if several drops are applied over several minutes just before the adjustment.

The need for an adjustment and the amount of the adjustment are determined by assessing the postoperative ocular alignment and versions. Access to the adjustable knot usually is achieved by having an assistant hold the eyelids open. An eyelid speculum also can be used, but it adds to patient's anxiety and may increase the chance of a vasovagal response.²⁷ If an adjustment is unnecessary, the slip knot is converted to a permanent knot and the suture ends are trimmed. If the muscle requires adjustment, the loop is cut and the suture end removed, being careful to leave the double throw intact.

To advance the muscle, the surgeon should gently pull up both ends of the adjustable suture and tighten the double throw to the desired amount (Fig. 11). The adjustment is easier if the tension on the adjusted muscle is decreased during the advancement. This is accomplished by having the patient attempt to look away from the field of action of the adjusted muscle while the globe is held in the primary gaze position by the assistant.

To recess the muscle further, the loop is removed and the surgeon's knot loosened the desired amount. The patient is asked to look in the direction of the field of action of the muscle while the globe is held in primary position. This maneuver usually causes the adjusted muscle to take up slack and tighten the knot (Fig. 12). Occasionally, especially if the adjustment has been delayed or after a reoperation, the muscle may adhere firmly to the sclera or surrounding fascia and limit the amount of adjustment possible. When this happens, I gently slide a small muscle hook under the muscle to break any adhesions. Others have incorporated “sweep” sutures for this purpose.¹⁸

If the sliding knot technique is used, the knot is adjusted by moving it along the adjustable sutures in the desired direction to tighten or loosen the muscle (Fig. 13). After the adjustment has been completed, the sutures are tied over the sliding knot with multiple throws and the excess ends trimmed.

PREFERRED POSITION OF ALIGNMENT

The ocular alignment often is unstable after strabismus surgery. In some cases, the ocular alignment several weeks after the operation may be different from the alignment found at the time of the adjustment. Adjustable sutures do not appear to affect the postoperative instability; however, they do provide an accurate determination of the initial postoperative eye alignment. Based on the type of preoperative strabismus and the operation performed, the experienced strabismus surgeon can anticipate the most likely change in the postoperative alignment and adjust the muscle or muscles accordingly. Table 1 lists the approximate desired alignment at the time of the adjustment according to the type of strabismus.

TABLE 1. Preferred Position of Alignment at the Time of Adjustment

Most patients who undergo surgery for a comitant exodeviation have a postoperative alignment drift in the direction of the preoperative deviation within the first 6 weeks after surgery. The average amount of drift is controversial. Keech and associates suggest that these patients should be esotropic between 5 and 15 prism diopters (Δ) at the time of adjustment to compensate for this drift.²⁸ This includes preoperative intermittent and constant deviations, as well as patients with exodeviations secondary to visual loss in one eye. Eino and Kraft found a smaller change in the alignment and recommended initial overcorrections between 3 and 7 Δ.²⁹ Schlossman and colleagues have shown that patients with exophoria who are visually mature have a relatively stable postoperative course and can achieve a good result if their ocular alignment is orthotropic or slightly undercorrected immediately after surgery.³⁰

The best initial postoperative position of alignment is less clear for esodeviation. Keech and associates found an average postoperative change in the ocular alignment of 6 Δ toward an overcorrection in 61 patients operative for esotropia with adjustable sutures.²⁸ Eino and Kraft noted only a 1-Δ average drift toward an overcorrection in 44 esotropic patients.²⁹ Although neither of these studies assess the effect of fusion on the change in alignment, most experts suggest that patients with esodeviation and good fusion potential are best adjusted to orthotropia or a slight exotropia (5 Δ or less). Patients with esotropia and poor fusion potential are thought to be more likely to drift toward an exodeviation. Therefore, the best adjustment position would be a small esodeviation.

The best initial postoperative position of alignment for vertical strabismus is difficult to determine, partly because of diverse causes. Keech and associates noted an average change in alignment of 4 Δ toward overcorrection in 44 patients with vertical deviations.²⁸ In a separate study of 47 patients with acquired vertical deviations, the same group found no differences in the outcomes with an initial slight over or undercorrection.³¹ Weston and colleagues noted a mean change of 1.5 Δ toward overcorrection for 22 patients with vertical deviations.³² Based on these studies, vertical deviations with minimal restriction or paresis probably are best aligned close to orthophoria. Patients with fusion may benefit from an adjustment to orthophoria or a slight undercorrection, since they usually have fusional amplitudes that help to control the deviation. Patients with inferior rectus muscle restriction as a result of thyroid-related eye disease or other conditions are thought to be prone to progressive overcorrections, although this is controversial.^33–35 In these cases, a small undercorrection may be reasonable.

The ocular ductions also must be considered during the adjustment. The surgeon should avoid situations where the preferred position of alignment at the time of the adjustment can be achieved only by creating a restriction or limitation of ocular ductions during the advancement or recession of the adjusted muscles. Although the initial alignment may be satisfactory, the unbalanced forces created will result in a significant overcorrection or undercorrection with time. To prevent this problem, surgery should be planned so that the adjusted muscle or muscles are not left at their maximally recessed position. For example, an adjustable recession of the lateral rectus and a resection of the medial rectus for a 40 Δ exotropia is likely to leave the lateral rectus recessed 8 to 9 mm from the original muscle insertion. If the patient is greatly undercorrected, additional recession of the lateral rectus during the adjustment is likely to limit abduction of the eye. A better choice would be to operate on three horizontal recti. This approach allows flexibility for a muscle to be advanced or recessed without limiting ductions.

Rarely, it may be impossible to perform the adjustment because the patient is too ill or emotionally unstable.⁴⁴ Careful selection and preparation of the patient usually prevents this situation. If it is not possible to perform the adjustment, the patient can be sedated or anesthetized, or the adjustment can be delayed up to several days.²⁶

The incidence of scleral perforation and the associated complications of retinal detachment or endophthalmitis using adjustable or nonadjustable techniques is low.⁴⁵ Theoretically, the use of adjustable sutures should decrease the risk of globe penetration and retinal detachment because the sutures usually are attached to the thicker sclera at the original muscle insertion, and the insertion site does not overlie the retina. The management of this complication after adjustable suture surgery is the same as for nonadjustable strabismus surgery.

The extra manipulation required with adjustable sutures may increase the possibility of a broken suture or slipped muscle compared with nonadjustable suture surgery. In 255 cases, Pratt-Johnson reports one slipped muscle.⁴⁴ In more than 400 procedures, Flynn had four broken sutures associated with two slipped muscles.⁴⁶ Keech and associates noted five suture knots untied before the adjustment and one that broke after the adjustment in 333 cases.²⁸ In most of these cases, the sutures were retied and the muscle readjusted without difficulty under topical anesthesia.

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