This chapter describes the basic and specialty instruments used in strabismus surgery. Included are discussions of specula, forceps, hooks, retractors, calipers, and needle holders.
22 Strabismus Surgical Instrumentation
Any carpenter or mechanic will tell you that having the right tools available can make the difference needed to insure efficient and high-quality workmanship. The same is true regarding surgical instruments employed in strabismus surgery.
Strabismus surgical instruments mostly consist of basic forceps, retractors, scissors, and so forth, which are available from a broad array of manufacturers and will be discussed here in general terms. There are a number of specialized instruments, most of more recent design, largely introduced by or available from a single manufacturer, which will be referenced.
Specula not only open the lid fissure, but also can be useful to keep eyelashes out of the surgical field. Most surgeons prefer a design with solid blades, such as the Lancaster speculum or Lieberman speculum (Katena). Another solid blade speculum with less hardware to catch sutures is the Wright bladed lid speculum (Titan Surgical). At times, a wire speculum (such as a Barraquer) is less bulky and affords more exposure posteriorly. For very posterior procedures, greater access can be obtained by removing the speculum and using a separate retractor.
Generally, toothed forceps are used to grasp tissue during strabismus surgery. The most common forceps is the Bishop-Harmon with 2 × 1 teeth (one tooth on one side and two on the other). These are available from heavy to fine. When grasping conjunctiva for globe positioning, it can be preferable to spread the potential tissue tearing forces over a larger area to minimize the risk of conjunctival damage. This is accomplished by using forceps with 3 × 2 teeth, such as a Lester forceps. Smooth toothless forceps can be employed for tying purposes.
For globe fixation during scleral passes, most surgeons employ a Castroviejo-type forceps with 2 × 1 0.5-mm teeth. These are available both straight and curved, and with or without a lock. Katena Products has developed a sliding lock mechanism that is less prone to inadvertent unlocking compared to the traditional spring lock. The curved Moody locking forceps (Katena) (Fig. 22‑1) can be draped nasally or temporally, allowing the surgeon to fixate the eye for scleral passes without an assistant.
There are two mechanisms for scissors operation—spring-loaded and ring scissors. Finer scissors generally employ the spring-loaded mechanism. To cut, the scissors are closed, compressing the spring. When released, the spring mechanism opens the scissors blades. The prototype example is the Westcott scissors, which generally has curved blades with either blunt or sharp points and in right and left configurations. The blunt Westcott scissors is well suited for general dissection of conjunctiva, Tenon’s fascia, and intermuscular septum. With a finer tip, the sharp Westcott scissors can be employed for more precise dissection and excision, and they are also useful as suture scissors. For muscle disinsertion or tenotomy, a Manson-Aebli corneal section scissors is often utilized. This spring action scissors, available in right and left configurations, has angled straight blades with blunt tips. The lower blade is slightly longer than the upper one to prevent accidental cutting of the sclera during tenotomy.
Larger scissors generally have ring handles without a spring mechanism. The surgeon provides the force to open the scissors by moving the rings apart. This is useful for blunt dissection, as the opening force of spring-loaded scissors is often insufficient to bluntly dissect tissue, especially in cases of reoperation with scarring. Examples include Stevens tenotomy scissors, as well as various iris scissors with blunt or sharp tips.
Strabismus hooks principally serve three purposes—to identify and isolate a muscle, to secure a muscle for operative steps upon it, and for general retraction purposes.
The Stevens hook is a small curved hook useful for initial identification and isolation of a muscle. As is true for essentially all hooks, a smooth and highly polished surface minimizes tissue drag and facilitates the steps of muscle surgery. The Stevens hook is also often employed as a retractor.
The Jameson hook has a smooth olive-tip bulb on its end, allowing passage through tissue but securing the muscle once isolated by preventing slippage of the muscle off the hook. It remains the most popular hook worldwide.
The Green hook has a straight flat platform perpendicular to the handle, with the end bent up much like the tip of a snow ski. This easily allows passage of the hook through tissue, but once the muscle is isolated the ski tip retains it on the hook. Additionally, the flat platform on the base of the hook can serve as a base or barrier to allow placement of sutures in the muscle while protecting the underlying sclera from inadvertent perforation.
The von Graefe hook is a larger version of the Stevens hook, capable of isolating an entire muscle, and at times also useful as a retractor.
The Manson double hook contains two small hooks, similar to Stevens hooks, placed several millimeters apart. The hook is malleable and the interhook distance is adjustable, making it useful for retraction purposes.
22.5.1 Protective Hooks
Extraocular muscles are at times very tight, which can increase the risk of scleral perforation during suture placement in the muscle insertion. This is especially true in the case of Graves’ disease, Möbius syndrome, and Duane’s syndrome. A variety of hooks have been developed to decrease the risk of inadvertent scleral perforation.
The Bishop hook (Katena) (Fig. 22‑2) utilizes a pivoting metal plate on the straight bottom portion of the hook. In use, this plate is positioned between the muscle and sclera, serving as a barrier so that sutures placed in the muscle insertion cannot perforate the sclera. 1
The Wright hook (Titan Surgical) (Fig. 22‑3) employs a groove in the hook that serves as a guide and barrier for placement of the muscle insertional suture, again protecting the sclera. It is available in right and left models.
The Suh hook (Ambler Surgical) (Fig. 22‑4) also employs a protective groove. It has a flat base with a semi-sharp ski tip to facilitate passage through scar tissue. It is also made in right and left models.
The Rychwalski hook (Katena) (Fig. 22‑5) has an olive tip similar to a Jameson, but with a protective groove on both sides of the flat portion, allowing a single hook to be used ambidextrously during muscle suture placement.
The Wilson-Dacamara hook (Fig. 22‑6) has an upturned end similar to a Green hook to retain the muscle, and incorporates protective grooves on opposite surfaces, again allowing a single hook to be used ambidextrously. It is manufactured by MSI Instruments.