Summary
In this chapter, the author will describe the pathology of pterygia with its relationship to the adjacent structure, the medial rectus. Pterygia that have developed on the nasal side of the eye are partially overlying the medial recti. Despite the fact that various techniques have been developed and employed to excise pterygia, recurrences are common. The scarring involving the medial rectus after surgery for primary or recurrent pterygia may restrict the abduction of the involved eye, resulting in an annoying and intractable diplopia in attempted horizontal gaze positions. The author will describe a surgical technique to treat restrictive strabismus following pterygium excision. Corrective surgery is performed by safely dissecting all of the scar tissue from the medial rectus. In some cases, a recession of this ocular muscle is also necessary. A conjunctival autograft is performed in all cases to cover the large conjunctival defect. The combination of all three essential steps of this surgical approach will restore motion and function of the medial rectus with relief of the diplopia.
14 Pterygium and Strabismus
14.1 Pathology of Pterygia
Hogan and Zimmerman describe pterygia as a degeneration of the conjunctiva. 1 The lesion is characterized by an elevated mass of thickened conjunctiva at the limbus. Microscopically, the epithelium is irregular and the collagen fibers are hypertrophic, dense, and hyalinized. The pathologic conjunctiva may develop granular basophilic material with many new vessels in the stroma and infiltration by large mononuclear connective tissue cells. Ninety percent of pterygia are found nasally, and these occur in the interpalpebral zone. The pathogenesis is unknown, but pterygia are thought to be the result of external irritants, which include wind, dust, and sunlight as causal agents.
Numerous techniques have been suggested to reduce the pterygium recurrence rate after excision. These methods have included the use of beta radiation and topical mitomycin C eyedrops as adjuncts to the surgical removal. 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 Both of these techniques may result in a long-term decrease in ocular circulation with thinning and necrosis of the sclera. This complication of necrosis may occur after many years following the pterygium excision.
Autografts of the conjunctiva have been utilized following the excision of primary and recurrent pterygia since the mid-1980s in an effort to help prevent scarring. 13 In addition, amniotic membrane grafts have been utilized in a manner similar to the autografts. 14 The recurrence rate following amniotic membrane grafting is 5 to 64%. 15 The rate of recurrence is reduced in some studies by adding intraoperative mitomycin C or by utilizing an extensive tenonectomy. 15 A randomized, controlled study of the use of a conjunctival autograft versus an amniotic membrane graft showed the superiority of autografts in reducing the rate of recurrence after primary and recurrent pterygium excision. 16 , 17 An excellent description of techniques utilized to help prevent recurrences was presented by Hirst in 2012. 15 This surgeon reported 1000 cases with an extremely low recurrence rate (0.1%). Hirst also recommends the use of an autograft rather than amniotic membrane to cover any conjunctival defect.
14.2 Injury to the Medial Rectus
Injury to the medial rectus (MR) by inadvertent disinsertion of this muscle has been reported following pterygium surgery. 18 , 19 In each of these four cases with loss of MR function, the pterygium surgeon recognized the deficient adduction in the operated eye and promptly referred the patient to a consulting strabismologist. Restoration of MR function was facilitated by early recognition of the complication, and in each case, the strabismologist was able to retrieve the disinserted MR and reattach it to the original insertion. All patients were able to regain normal binocularity. This complication of disinsertion of the MR during pterygium surgery denotes that extreme care must be taken when dissecting the pterygium from underlying tissue, which may include the MR.
14.3 Restrictive Strabismus following Pterygium Excision
Much more common than disinsertion of the MR is the scarring involving the MR that may develop following pterygium excision. 20 The patients complain of diplopia, which is worse in attempted abduction following pterygium excision. The affected eye has deficient abduction in the field of gaze opposite the injured muscle. In this author’s experience, many patients with only minimal diplopia do not seek further surgery. There is, however, a small but very unhappy group of patients with diplopia who have sought relief from their plight.
There have been few publications addressing the problem of restrictive strabismus following pterygium excision. Ela-Dalman et al reported seven cases in which dissection of the scar tissue and supplementary MR recession was found to be helpful to relieve the incomitant strabismus following pterygium excision. 20 Strube et al reported that the use of amniotic graft tissue was helpful as an adjunct to cover large conjunctival defects following the surgery to relieve restrictive strabismus (Video 28.2, Video 28.3). 21
14.4 Repair of Restrictive Strabismus in Three Patients—Author’s Experience
14.4.1 Diagnosis
All three patients lacked the ability to fully abduct the affected eye. Two of the patients reported diplopia for distant objects in all fields of gaze. In one of the patients, the diplopia was limited to side gaze on attempted abduction of the affected eye. None of the patients reported diplopia for near objects. All patients had to resort to covering the affected eye to avoid diplopia while driving an automobile. Prism cover measurements showed a greater amount of misalignment when the patient was attempting to abduct the affected eye. There was a markedly positive forced duction test in all cases before the corrective surgery was performed.
14.4.2 Review of the Records of the Previous Surgery
The author has found it helpful to review all the records of previous surgery. In all three cases, no muscle hook was utilized to help identify the MR during the initial or subsequent pterygium surgery. The omission of this critical maneuver probably led to the failure by the initial surgeon to excise the scar tissue overlying the involved MR during the initial and secondary surgery.
14.4.3 Preoperative Testing and Planning
Preoperative prism measurements are made in right, central, and left gaze positions to quantitate the strabismus. Versions and ductions of the horizontal recti are evaluated for distance and near targets.
14.4.4 Techniques Employed during the Corrective Surgery
The author prefers to use general anesthesia in these cases due to the difficulty in dissecting the extensive scar tissue complex involving the MR, but sub-Tenon’s anesthesia can also be used. Also helpful is the use of an operating microscope to clearly identify the scar tissue overlying the MR. When dissecting the scar tissue from the underlying MR, it is essential to have a large muscle hook under the MR (Fig. 14‑1). Traction on this muscle hook will cause the scar tissue to separate slightly from the MR, thus allowing a plane to be developed between the two structures. An autograft at the end of the procedure will help close the large conjunctival defect and help prevent recurrence of the pterygium. (The details are specified in Chapter 28.)
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