Surgery of the rectus muscles is the most common form of strabismus surgery performed. An understanding of anatomy, careful planning, and excellent surgical technique are required for an optimal result. Preparation includes careful measurements of strabismus preoperatively, preferably in primary position at distance and near, at distance in upgaze and downgaze (to tease out A and V patterns), and in side gazes to ascertain lateral incomitance. If the patient is old enough and cooperative enough, horizontal fusional amplitudes are also useful. This author usually places the final muscle position in the middle of the fusional amplitude range. The major focus of this chapter is on surgical technique. Meticulous attention to detail during the operative procedure results in minimal scarring and minimal inflammation. An optimal surgical result has many facets. In young children, realigning the eyes may facilitate and allow close to normal development of the visual sensory system, which requires alignment of the eyes to develop normally. In adults, it may restore components of a previously developed binocular system that were not manifesting because of the strabismus, and/or it may eliminate diplopia. An additional goal is to restore to normal appearance, not an enhancement, but a restoring to normal appearance of the eyes. This enables eye contact for communication. In addition, in many cultures, strabismus or misalignment of the eyes is viewed as the “evil eye” and has a negative effect on the life of the patient. Also, excellent surgical technique results in minimal postoperative discomfort.
23 Classic Strabismus Surgery: Rectus Muscle
This chapter is essentially the Marshall Parks approach to rectus muscle surgery. He was a superb, meticulous, and efficient surgeon whose techniques have stood the test of time. We will begin with his fornix approach, then address his emphasis on understanding the anatomy, carefully identifying the muscle poles, and isolating the muscle with care and attention to adjacent tissues. His surgical philosophy included a move away from the then prevalent tendency to cut tissues around the eye muscles. He recommended maintaining the muscle capsule, and for recessions, minimizing the cutting of check ligaments. There is more dissection required for resections as described below, but in dissecting, the muscle capsule should remain intact.
Of course, with time and many surgical procedures, one adds one’s own nuances, and those are included here as well (Video 23.1, Video 23.2, Video 23.3, Video 23.4).
23.2 Everything’s Set
Needless to say, a great deal of thought and planning goes into the procedure before entering the operating room. Table 23‑1 and Table 23‑2 present guidelines for surgical dosages for horizontal muscle surgery and provide time-tested numbers for surgical planning. These dosages have been derived from Dr. Marshall Parks. Modifications have occurred over the years by his fellows in response to their own surgical results. Despite this, things have not changed very much. The virtue of this constancy should be attributed to Dr. Parks. These numbers apply to surgeries performed in the manner described in this chapter. Modifications in technique may alter results, and at the very best, these are guidelines.
Dr. Ludwig prefers smaller resections to create less bulk over the insertions and will sometimes reduce the resection by 1 or 2 mm and increase the recession by the same amount, in single-eye procedures.
In the operating room, writing the plan on a board is helpful to avoid errors. One may choose to alter the plan if unforeseen events occur, but it is best to have the original plan displayed.
The patient’s head position and stability should be checked by the surgeon before prepping, to make certain it is optimal. I prefer the top of the head to be flush with the top of the table for best access during the procedure.
The surgeon’s and assistant’s chair heights and positions should be comfortable and provide good viewing (loupes, working distance) to address the task at hand.
As with any strabismus procedure, the first step following placement of the speculum is forced ductions (Chapter 3).
23.3 The Fornix Incision
The fornix incision allows for minimal suturing of the conjunctiva and, therefore, greater postoperative comfort for the patient. Greater comfort results in less postoperative manipulation by the patient, especially if the patient is a child. The medial rectus (MR) and inferior rectus (IR) are accessed in the inferior nasal quadrant. The lateral rectus (LR) is approached from the inferior temporal quadrant and the superior rectus (SR) from the superior temporal quadrant.
To access the fornix (right eye, LR recession), the assistant grasps the limbus at the 4:30 o’clock position with the toothed 0.5-mm forceps and elevates and adducts the eye to expose the inferior and temporal quadrant. Next, identify the inferior pole of the LR muscle and the lateral pole of the IR muscle through the conjunctiva. Using the blunt Westcott scissors, make a small (2-mm) incision in the conjunctiva parallel to the limbus, about 8 mm posterior to the limbus, avoiding moving too far into the fornix where the extraconal fat bad lies beneath (about 10 mm from the limbus); this should not be breached, because this will result in bleeding and scarring (Fig. 23‑1). The curved blade of the Westcott scissors can then be placed in the conjunctival opening, with the curve parallel to that of the limbus, to extend the wound symmetrically placed in the inferior temporal quadrant so that it is about 8 mm long. The exposed Tenon’s capsule is then grasped by the surgeon and assistant with Bishop-Harmon forceps and tented up. The surgeon cuts down to sclera on this tent in a radial direction (Fig. 23‑2). Spread with the Westcott scissors (curved down), parallel to the curve of the globe beneath the Tenon’s capsule into the inferior temporal quadrant.
23.4 Isolate the Muscle
For the horizontal muscles, we will be hooking the inferior pole. Using the Stevens hook, with the toe on the episclera and then rotating, hook the inferior pole (remember the spiral of Tillaux; the MR pole should be about 5.5 mm from the limbus and the LR pole should be about 6.9 mm from the limbus) (Fig. 23‑3). Don’t place the hook well behind this to “make sure you get it all.” This is “deep dipping,” which you do not want to do because you can reach the intraconal fat pad if you are beneath the muscle, or the extraconal fat pad if you have slipped superficially to the muscle. Either way, breaching the fat pad causes scarring and should be avoided. Hooking the pole with the small Stevens hook allows you to safely identify the pole for the subsequent placement of the large hook (Green or Jameson) (Fig. 23‑4). Once the Stevens hook has engaged the inferior pole of the muscle, push the toe toward the sclera to elevate the inferior border of the muscle for placement of the large hook. For the Green hook, slide it next to the Stevens hook, metal against metal, and tilt so that the plane of the sclera is parallel to the bent portion at the tip rather than the long base of the hook (Fig. 23‑5). This will avoid catching the toe of the hook on the underbelly of the muscle. Once you get beyond the superior border of the muscle, tilt the tip away from the sclera to hold the superior border. Remove the Stevens hook and place the second Green hook just distal to the first and then remove the first. Swing the toe of the Green hook toward the limbus to confirm that all fibers of the muscle are on the hook (Fig. 23‑6). If the heel rotates rather than the toe, then fibers are missing and another Green hook should be placed just distal to the first and the first removed.
Once the entire muscle is on the hook, place the heel of the Green hook against the lower blade of the speculum, and with the Stevens hook, pull the overlying conjunctiva and Tenon’s capsule over the toe of the large hook. You may need to pull the excess Tenon’s capsule off at the toe of the hook with the Bishop-Harmon forceps (Fig. 23‑7). Then, grasp the superior intermuscular septum with the Bishop-Harmon forceps (on the toe of the large hook) and cut a hole in it with the Westcott scissors (Fig. 23‑8). Slip the toe of the large hook through the hole.