The most common incision used to access the extraocular muscles in strabismus surgery is the limbal incision.1 The fornix incision is an alternative to the limbal incision and was first described by Parks in 1968.2 Despite having some key advantages over the limbal approach, the fornix incision is not commonly used or taught in the United Kingdom.
The fornix incision has been used for more than a year in our center with promising results. Our aim in this article is to revisit the fornix incision. We propose a modified version of the Parks technique that takes into account modern operating equipment. We have created a video demonstration with the goal of bringing the fornix incision to the attention of strabismus surgeons. We discuss the advantages and disadvantages of this technique.
Although equipment has been designed specifically to facilitate this technique, our method uses only the equipment available in a standard strabismus setting.3 This procedure is always performed under general anesthesia and under the operating microscope.
A stay suture is placed in the inferior corneoscleral limbus. Using artery forceps, the suture is used to hold the eye in elevation and abduction for medial rectus access or in elevation and adduction for lateral rectus access.
The incision is made parallel to the forniceal cul-de-sac, in the inferior bulbar conjunctiva. For medial rectus procedures, the incision extends from the medial border of the inferior rectus muscle to the lower edge of the plica. For lateral rectus procedures, the 8-mm incision extends laterally from the lateral border of the inferior rectus muscle. Through the conjunctival fornix incision, Tenon’s capsule is grasped and incised until bare sclera is reached.
The Chavasse squint hook is then used to locate and hook the desired rectus muscle through a single sweep. This step is repeated if there is a suspicion that the whole muscle has not been included on the hook.
Using a small hook, the conjunctiva is rotated and retracted superiorly until it clears the toe of the Chavasse hook, exposing the rectus muscle. This procedure is performed bimanually with simultaneous inferior and temporal rotation of the Chavasse hook toward the conjunctival incision.
The assistant tents up the intermuscular septum at the superior edge of the muscle and this is divided to delineate the superior muscle border. The Tenon’s capsule is then dissected off the muscle to expose the muscle fibers.
The recession or resection is performed in the usual manner.
Comparison With Parks’ Original Technique
In the original Parks technique, the operating assistant held the eye immobilized. A corneoscleral stay suture negates the need for an assistant and removes a set of forceps from the operating field.
Although initially isolating the muscle, the Parks technique describes using three differently sized hooks to progressively engage the muscle. This technique takes account of the credible risk that the blindly passed hook could split the muscle rather than clearing the superior border. If such an error were not recognized and rectified, the success of the operation would be adversely affected. This is particularly important to consider in training stages, but with an experienced surgeon the muscle can be successfully hooked on the first pass using one large hook. Routine thorough inspection of the insertion site after detaching the muscle is necessary to ensure that the entire muscle has been adequately isolated.
In our experience, using the Parks technique of leaving the conjunctiva unsutured results in an unnecessarily unsightly scar. This is avoided by closing the conjunctiva with one to two 6-0 polyglactin sutures.
Our modified technique allows the flexibility of using adjustable sutures and of superior transposition of the muscle should this be required.
Advantages of the Fornix Incision
The rectus muscle is accessed with greater ease and speed than with the limbal incision.4 One incision can be used to access more than one muscle (eg, lateral rectus and inferior rectus). Minimal disruption is made to the normal anatomy. Because disruption is minimal, there are fewer postoperative episcleral adhesions, which facilitates re-access in the event that a second surgery is required. By avoiding the limbal incision, the risk of disruption to perilimbal episcleral vessels is reduced, decreasing the potential for anterior segment ischemia.5 Closure of the wound is also simple. The scar is small and within the fornix, so is covered by the eyelids postoperatively. This yields an improved cosmetic outcome and greater postoperative comfort. In comparison, the limbal scar is large and necessitates uncomfortable interpalpebral sutures.
The fornix incision is particularly valuable in “re-do” procedures (after initial surgery via the limbal approach) because it provides excellent muscle access without the need to dissect the anterior scarred conjunctiva that is prone to buttonholing.
The fornix incision can be converted mid-operation to a limbal incision or combined with a modified Swan incision. This is advantageous if the anatomy is found to be unusual or the surgeon requires more full exposure.
Limitations of the Fornix Incision
The limitations of the fornix incision are related to the increased technical difficulty of having a smaller field of exposure. As discussed, there is a risk of splitting the muscle tendon. Reduced exposure increases the risk of hooking the wrong muscle and hemorrhage. Consequently, the fornix incision may be daunting to trainee surgeons, but these difficulties can be overcome in most cases with modern microscopic techniques and supervised training.
Larger recessions can be accomplished through the fornix incision by using the hang-back method of muscle placement. We have been able to perform recessions as large as 10 mm through this approach. However, in some cases it may become necessary to convert the fornix incision to a limbal incision.
There is potential for the conjunctiva to become plicated after resection of the medial rectus muscle. This is avoided by accurate tissue plane dissection. We routinely close the conjunctiva with interrupted 6-0 polyglactin sutures, which prevents Tenon’s capsule prolapse.
The fornix incision relies on conjunctival flexibility. In patients older than 40 years, the conjunctiva is thinner and more friable so the fornix incision is associated with an increased risk of conjunctival tearing in this group. However, Coats has proposed that the fornix incision offers important potential advantages to older patients notwithstanding the risks of conjunctival tear.6
The Parks fornix incision technique originally purported the advantages of both minimizing and hiding the scar. Minimally invasive surgical techniques are increasingly important (and common) in modern surgery because they minimize trauma to tissues, facilitate postoperative healing, and increase postoperative patient comfort.
Mojon has proposed minimally invasive strabismus surgery and demonstrated the feasibility of an approach to strabismus surgery using minimal dissection.7 In Mojon’s approach, radial incisions are made superior and inferior to the rectus muscle; a tunnel is formed between the two incisions, allowing access to the muscle without full visualization of the surgical field.
The fornix incision provides a middle ground between the standard, open limbal approach and techniques such as minimally invasive strabismus surgery. For the reasons discussed, the fornix incision is a feasible alternative to the limbal approach. Our technique requires only standard strabismus equipment. Although the fornix incision does not provide as full a view of the anatomy as the limbal incision, it provides sufficient exposure to reposition a muscle with a small, hidden scar and with minimal anatomical disruption.