In some cases, the angle of strabismus is too small to warrant full muscle recession or resection due to a substantial risk of overcorrection, but patient symptoms require some surgical intervention. Mini-procedures have been developed to correct small deviations with little risk of overcorrection. Some are so noninvasive that they may be performed in the office.
Muscle strengthening mini-procedures include the angled resection and mini-plication. Weakening procedures include multiple myotomies, angled recession, graded partial rectus muscle tenotomy, mini-tenotomy, and marginal disinsertion.
34 Mini-Procedures and Compartmental Surgery for Small Angle Strabismus
Individuals who develop small angle strabismus but are not habitual glasses wearers are not easily coaxed into wearing prism glasses. Their symptoms are disconcerting and sometimes disabling. Many of these patients are elderly and do not easily tolerate the stress and risk of operating room surgical procedures, particularly those requiring general anesthesia. Mini-procedures are those that provide a small effect with little manipulation of the eye. Some may be performed in the office under topical anesthesia, and all may be performed with local anesthesia in an operating room setting.
34.2 Correction of Muscle Displacement
Muscle displacement may begin gradually due to loss of collagen strength with aging. The most commonly affected muscle is the lateral rectus, which sags inferiorly in the elderly, causing divergence insufficiency esotropia. Although mini-procedures could be temporarily helpful here, and a superiorly placed, angled resection of the lateral rectus could be partially curative by lifting the sagging muscle, the simple myopexy procedures detailed in Chapters 19 and 30 are preferred, as they correct the source of the deviation. Additionally, there are often small cyclovertical components to the deviation, which are all corrected by simple restoration of the muscle’s path.
34.3 Strengthening Procedures
34.3.1 Office Strengthening Procedure—Mini-Plication
Wright developed the mini-plication as a simple office approach to strengthen a muscle and correct an average of 5.5 to 9 prism diopters deviation of a vertical or horizontal rectus muscle (Fig. 34‑1). 1 The group with an average 5.5 diopter correction had mini-plication alone, and the group with 9 diopters average correction had undergone previous weakening surgery of the antagonist muscle. The eye receives topical lidocaine gel, followed by topical tetracaine, phenylephrine 2.5%, and antibiotic solutions. A Swan conjunctival incision is made over the insertion of the rectus muscle, and sclera is cleaned of loose connective tissue for a distance of 2 mm anterior to the insertion. The eye is held with a toothed forceps and rotated away from the direction of action of the muscle, in order to reach a posterior location on the muscle. The conjunctival incision is extended to 6 mm posterior to the muscle insertion, and the muscle is grasped centrally with 0.5-mm toothed forceps 5 mm behind the insertion, incorporating a 3- to 4-mm width of muscle tissue. The muscle is lifted with the forceps, and a 6–0 polyglactin suture is passed under the central 3 to 4 mm of muscle tissue, avoiding the anterior ciliary vessels. A knot is tied over the central muscle tissue, and then sutured to sclera 0.5 mm anterior to the insertion, plicating the center of the muscle, and the conjunctiva is closed with an absorbable suture. Wright recommends combining mini-plication of one or more muscles with mini-tenotomies of antagonist muscles (see below) in staged fashion to correct larger or recurrent deviations.
34.3.2 Operating Room Strengthening Procedure—Angled Resection
This author has found small angled resection to be helpful to correct small deviations in which only a small strengthening is needed (Fig. 34‑2, Video 34.1, Video 34.2). When performed on the inferior half of the medial rectus, it is particularly useful to treat convergence insufficiency, alone (if the eyes are straight for distance) or in combination with lateral rectus recession (for substantial distance exodeviation). Advantages over a full resection are the decreased violation of tissue, which therefore leads to decreased discomfort and swelling, as well as the preservation of half of the anterior ciliary vessels. There is preservation of half of the normal insertion, which would decrease the impact of any healing abnormality such as stretched scar, were it to occur. Angled resection may also confer a small muscle belly shifting effect to help correct muscle displacements (Chapter 19). For example, when there is a sagging lateral rectus muscle, placing the angled resection at the superior pole may help to lift the muscle belly, due to differential shortening of only the superior muscle pole fibers. Another potential advantage is that angled resection may be directed at one muscle compartment alone, allowing targeted correction of an isolated compartmental weakness (Chapter 4). Although angled resection may be titrated as in a full-width resection, it is impractical to perform one greater than 5 mm, so the usual amount is 3 to 5 mm.
The rectus muscle is isolated through a fornix incision as described in Chapter 23. The muscle is spread out on two Green hooks, but dissection is only performed over the section to be resected. A 6–0 polyglactin suture on an S-29 needle is placed through the muscle beginning at the measured distance from the insertion at the desired pole of the muscle. For example, for a superior angled resection, the suture begins at 5 mm behind the insertion at the superior pole, but is passed in a straight line, angled so that it reaches the midpoint of the insertion. A small lock bite is taken at either end where the suture enters and exits the muscle, and the small wedge of muscle tissue distal to the suture is excised with Westcott scissors. Locking 0.5-mm forceps are placed on the denuded insertion, and the muscle is then sutured back to the original insertion as in any resection.