Accidental extraocular muscle damage during pterygium excision is a rare but serious complication. Medial rectus muscle disinsertion occurs more in recurrent large nasal pterygia. We report a rare case of medial rectus muscle disinsertion after pterygium surgery, that was attached to its original site via a pseudotendon/stretched scar tissue.
A 45-year-old woman presented to our strabismus clinic with complaints of diplopia for 1 month. She had a history of surgical excision of the nasal pterygium of her left eye at an outside secondary eye care center, after which she developed horizontal diplopia immediately and was not able to adduct her left eye. Therefore, she was referred to our center for further evaluation.
Systemic examination was within normal limits. Best corrected visual acuity in both eyes was 6/12. Anterior segment examination showed nasal conjunctival scarring in the left eye and grade II nasal pterygium in the right eye. She had bilateral immature senile cataract with nuclear sclerosis grade I with a cortical component. Fundus findings were normal. The patient had a right face turn. There was exotropia of the left eye and adduction was possible only up to the midline. On Hirschberg testing, there was exotropia of the left eye of approximately 15 degrees. On covering the right eye, the left eye was taking fixation, which was central. On prism bar cover testing, there was 30.00 diopters (D) of exotropia in the primary position when the right eye was fixing and more than 50.00 D of exotropia when the left eye was fixing. Deviation was maximum in dextroversion. Figure 1 shows the nine-gaze photograph of the patient preoperatively at the time of presentation. Forced duction testing was done, which was negative for the lateral rectus muscle of the left eye. Diplopia charting showed horizontal diplopia in all gazes with maximum separation in dextroversion (Figure 2A). Hess charting showed underaction of the medial rectus muscle of the left eye and over-action of the lateral rectus muscle of the right eye (Figure 3A).
Preoperative nine-gaze photograph shows left eye exotropia and limitation of adduction.
(A) Preoperative diplopia chart shows horizontal crossed diplopia in all gazes with maximum separation in dextroversion. (B) Postoperative diplopia chart shows no diplopia in primary position and minimal horizontal diplopia in extreme dextroversion.
(A) Preoperative Hess chart shows underaction of the left medial rectus muscle and overaction of the right lateral rectus muscle. (B) Postoperative Hess chart shows no limitation of extraocular movements.
Based on the above clinical history and findings, we made a diagnosis of medial rectus muscle disinsertion of the left eye after pterygium surgery. Medial rectus exploration surgery was done under local anesthesia. During exploration, we found an abnormal attachment of the medial rectus muscle that had features of a slipped muscle and some scar tissue. A slipped medial rectus muscle was found attached to the globe only through the pseudotendon (Figure 4). The capsule was dissected, the scar tissue was excised, and the slipped medial rectus muscle was identified, hooked, and secured with sutures. The muscle was reattached with advancement.
Intraoperative image of stretched scar/pseudotendon and slipped medial rectus muscle.
On postoperative day 1, the patient was orthotropic with mild conjunctival congestion of the left eye. There was no diplopia in primary position and minimal horizontal diplopia in extreme dextroversion that was confirmed on diplopia charting (Figure 2B). Extraocular muscle movements were full and there was no limitation on the Hess chart (Figure 3B).
The patient subsequently underwent uneventful pterygium surgery of the right eye followed by bilateral cataract surgery at our center. Visual acuity in both eyes was 6/6. Orthoptic examination at 6 months postoperatively demonstrated orthotropia and no diplopia. Figure 5 shows the nine-gaze photograph of the patient at 6 months of follow-up.
Postoperative nine-gaze photograph shows the patient was orthotropic with improvement in adduction at 6 months.
Pterygium is a degenerative condition characterized by wing-shaped fibrovascular outgrowth of conjunctiva over the cornea.1,2 In advanced cases, when pterygium is obscuring the visual axis, causing significant astigmatism, or is cosmetically unacceptable, surgical excision and placement of a conjunctival autograft or amniotic membrane is the treatment of choice.2–4 Different possible complications of pterygium surgery are conjunctival buttonhole, globe perforation, pyogenic granuloma formation, infection, dellen formation, recurrence of pterygium, and disinsertion of the medial rectus muscle.2,5,6
Inadvertent medial rectus muscle disinsertion is a rare complication of pterygium surgery, especially in cases of recurrent pterygium with excessive scarring, an extensive pterygium, or in the hands of an inexperienced surgeon.2,5 Disinsertion of the medial rectus muscle should be suspected when the patient presents with a large angle of deviation and limitation of adduction after pterygium surgery.
Types of disinserted medial rectus muscle are classified according to their morphological characteristics and appearance. A lost muscle occurs when there is absence of any attachment of muscle to the sclera. A slipped muscle occurs when the rectus muscle retracts posteriorly within the muscle capsule, with the empty capsule, which looks like a thin translucent membrane, remaining attached to the sclera.7,8 Clinically, a person with a slipped or lost muscle presents shortly after surgery with a large deviation of the eyeball. Stretched scar is a condition in which the rectus muscle is attached to the sclera by a segment of amorphous scar tissue rather than by a tendon or muscle, also termed pseudotendon.9 Gradual changes in eyeball deviation, over a period of several months, occur in cases of stretched scar. However, it is difficult to differentiate stretched scar and slipped muscle because some muscles contain features of both stretched scar and slipped muscle and are classified as “abnormal attachment,”7,8 as in our case. Different case reports of medial rectus muscle disinsertion after pterygium surgery have showed the medial rectus muscle located more posteriorly in the inferonasal quadrant,2,5 but in our case the slipped medial rectus muscle was attached to its original site via a pseudotendon/stretched scar tissue.
Surgical exploration in cases of disinserted medial rectus muscle should be done immediately after the complication is recognized to increase the possibility of finding the disinserted muscle. A delay in treatment can decrease success rates due to the formation of fibrous tissue around the detached muscle and contracture of the antagonist muscle.10
In our case, even on delayed presentation and formation of some scar tissue, the results were satisfactory due to a meticulous surgical approach and precise excision of the scar tissue.
- Farjo QA, Sugar A. Pterygium and conjunctival degenerations. In: Wiggs JL, Miller D, eds. Yanoff & Duker Ophthalmology, 3rd ed. Philadelphia: Mosby Elsevier; 2009:248–249. doi:10.1016/B978-0-323-04332-8.00033-0 [CrossRef]
- Patikulsila P, Apivatthakakul A, Seresirikachorn K. Recovery of a disinserted medial rectus muscle after pterygium surgery. Strabismus. 2018;26:142–144. doi:10.1080/09273972.2018.1465104 [CrossRef]
- Malozhen SA, Trufanov SV, Krakhmaleva DA. Pterygium: etiology, pathogenesis, treatment [article in Russian]. Vestn Oftalmol. 2017;133:76–83. doi:10.17116/oftalma2017133576-83 [CrossRef]
- Ang LP, Chua JL, Tan DT. Current concepts and techniques in pterygium treatment. Curr Opin Ophthalmol. 2007;18:308–313. doi:10.1097/ICU.0b013e3281a7ecbb [CrossRef]
- Ugrin MC, Molinari A. Disinsertion of the medial rectus following pterygium surgery: signs and management. Strabismus. 1999;7:147–152. doi:10.1076/stra.18.104.22.1681 [CrossRef]
- Ela-Dalman N, Velez FG, Rosenbaum AL. Incomitant esotropia following pterygium excision surgery. Arch Ophthalmol. 2007;125:369–373. doi:10.1001/archopht.125.3.369 [CrossRef]
- Negishi T, Hikoya A, Isoda H, et al. Magnetic resonance imaging of the medial rectus muscle of patients with consecutive exotropia after medial rectus muscle recession. Ophthalmology. 2010;117:1876–1882. doi:10.1016/j.ophtha.2010.02.006 [CrossRef]
- Jung JH, Leske DA, Holmes JM. Classifying medial rectus muscle attachment in consecutive exotropia. J AAPOS. 2016;20:197–200. doi:10.1016/j.jaapos.2016.02.008 [CrossRef]
- Ludwig IH. Scar remodeling after strabismus surgery. Trans Am Ophthalmol Soc. 1999;97:583–651.
- Plager DA, Parks MM. Recognition and repair of the “lost” rectus muscle: a report of 25 cases. Ophthalmology. 1990;97:131–137. doi:10.1016/S0161-6420(90)32636-2 [CrossRef]