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The Official Scientific Journal of Delhi Ophthalmological Society
Consecutive Exotropia: A Case Report and Review of Literature
Neha Singh, Vinita Singh
Dept of Ophthalmology, King George’s Medical University, Lucknow, Uttar Pradesh, India
Corresponding Author:
Neha Singh 
MBBS, MS, DNB
Department of Ophthalmology,
King George Medical University, Lucknow
Uttar Pradesh-226003, India
Email id: nhsngh.89@gmail.com
Published Online: 01-NOV-2018
DOI: http://dx.doi.org/10.7869/djo.398
Abstract
Consecutive exotropia is a manifest exotropia that develops in a formerly esotropic patient. Management of consecutive exotropia is rendered difficult due to scarring from previous surgery, lack of well established surgical dose corrections, high incidence of late exodrifts and requirement of multiple surgeries. We present a case of consecutive V pattern exotropia with mixed amblyopia in the left eye, managed in a staged surgery. 
Keywords : Consecutive exotropia, Medial rectus, Amblyopia, Musle slippage
Introduction
Consecutive exotropia is a manifest exotropia that develops in a formerly esotropic patient after surgical treatment for esotropia. The incidence of consecutive exotropia reportedly varies between 3% and 20% (wide variation due to different follow up in different studies, longer follow up studies documented a greater incidence).1-4 Risk factors include adduction deficit, amblyopia, anisometropia, A or V pattern, dissociated vertical deviation (DVD), hypermetropia, absent or poor binocularity and iatrogenic causes (i.e., previous medial rectus recession of >7 mm, multiple surgeries, miscalculation).1-3 Management of consecutive exotropia is rendered difficult due to scarring from previous surgery, lack of well established surgical dose corrections, high incidence of late exodrifts and requirement of multiple surgeries. We present a case of consecutive V pattern exotropia with mixed amblyopia in the left eye, managed in a staged surgery. 

Case Discussion
A 14 year old male presented to our institute with outward deviation of the left eye since 4 years. He gave history of squint correction surgery for esotropia performed seven years back. He was using hypermetropic glasses for 7 years. Old records showed history of left medial rectus (LMR) recession 4.5 mm and left lateral rectus (LLR) resection 6 mm 7 years back. The patient was on part time occlusion therapy for amblyopia. On examination, the best corrected visual acuity was 6/6 in the right eye and 6/18 in the left eye. Cycloplegic refraction revealed hypermetropia of 4 DS in the left eye. Hirschberg test showed exotropia of 30° in the left eye. Prism bar cover test (PBCT) demonstrated exotropia of 70 prism dioptre (PD) fixing each eye in primary gaze, 60 PD in down gaze and 80 PD in upgaze. Limitation of movement of left eye in adduction was elicited on testing ocular movements. Bilateral inferior oblique overaction was also present (Figure1). So the patient had consecutive exotropia with V pattern.



Based on these findings, the patient was planned for LMR resection (3 mm) + LMR advancement (4.5 mm) under local anaesthesia as first procedure. No muscle slippage was noted during surgery (the distance of the medial rectus muscle from the limbus matched medial rectus recession mentioned in previous records). There was no excessive scarring from previous surgery. Post-operatively, the patient had residual exotropia of 30 PD and his adduction had improved (Figure 2).
Left lateral rectus recession was done as a secondary procedure 1 month after the first procedure. The patient had 20 PD of exotropia with good control for near after the second procedure. At 6 month follow up, the patient was orthotropic for near with 20 PD exotropia for distance.




Discussion
Consecutive exotropias are manifest exotropias that occur following surgery for esotropia. Consecutive exotropias are much more common than consecutive esotropias. Most of the previous studies have shown time duration of 8.7-30 years between surgeries for esotropia to exotropia. Risk factors include adduction deficit, amblyopia, anisometropia, A or V pattern, dissociated vertical deviation (DVD), hypermetropia, absent or poor binocularity and iatrogenic causes (ie, previous medial rectus recession of >7 mm, multiple surgeries, miscalculation).1-3
In a study of 20 patients with consecutive exotropia, medial rectus slippage was found to be present in about 1/3 of patients.5 In this study, medial rectus advancement effectively treated consecutive exotropia without regard to muscle slippage. Most of the previous studies have advocated medial rectus advancement as the first step for consecutive exotropia in the presence of preoperative adduction deficit. These studies have shown dose effect relationship of medial rectus advancement for consecutive exotropia as 3-5 PD/mm.6-8 However, Mohan et al9 advocated unilateral lateral rectus recession and medial rectus resection and they found no significant advantage of adding medial rectus advancement.
Muscle slippage is a common cause of consecutive exotropia. Muscle slippage may occur immediately with limited ductions after strabismus surgery, but it may also occur progressively.10,11 Signs of acute medial rectus muscle slippage include a large exotropia associated with limited adduction and palpebral fissure widening on adduction.12,13 Detection of acute muscle slippage is not difficult. However, delayed medial rectus slippage, thought to be more common, may not be as easily recognized.11-13 Ludwig and Chow11 attributed this to stretched scar, an amorphous connective tissue interposed between an operated muscle tendon and sclera that presents with minimal or no version limitation, less separation of the tendons from the sclera, and thicker appearance of the scar segments. 
Management of consecutive exotropia is challenged by occurrence of late exodrift. Considering this late post operative exodrift, some authors have suggested to aim for overcorrection of 10-15 PD in visually mature patients.4,5
Thus, to conclude, medial rectus advancement is preferred in the first stage for consecutive exotropia because it allows surgical exploration of the medial rectus muscle to detect the presence of an unfavorable insertion. Postoperative exodrift should be considered when determining the target angles for consecutive exotropia surgery. Although medial rectus advancement reliably corrected exotropia in the immediate postoperative period, patients should be counseled that eventual recurrence of exotropia is likely.

References
  1. Ganesh A, Pirouznia S, Ganguly SS, Fagerholm P, Lithander J. Consecutive exotropia after surgical treatment of childhood esotropia: a 40-year follow-up study. Acta Ophthalmol 2011; 89:691-5. 
  2. Folk ER, Miller MT, Chapman L. Consecutive exotropia following surgery. Br J Ophthalmol 1983; 67:546-8. 
  3. Stager DR, Weakley DR, Jr, Everett M, Birch EE. Delayed consecutive exotropia following 7 millimeter bilateral medial rectus recession for congenital esotropia. J Pediatr Ophthalmol Strabismus 1994; 31:147-52. 
  4. Donaldson MJ, Forrest MP, Gole GA. The surgical management of consecutive exotropia. J AAPOS 2004; 8:230-36. 
  5. Gesite-de Leon B, Demer JL. Consecutive exotropia: why does it happen, and can medial rectus advancement correct it? J AAPOS 2014; 18:554-8.
  6. Cho YA, Ryu WY. The advancement of the medial rectus muscle for consecutive exotropia. Can J Ophthalmol 2013; 48:300-306. 
  7. Marcon GB, Pittino R. Dose–effect relationship of medial rectus muscle advancement for consecutive exotropia. J AAPOS 2011; 15:523-6.
  8. Chatzistefanou KI, Droutsas KD, Chimonidou E. Reversal of unilateral medial ectus recession and lateral rectus resection for the correction of consecutive exotropia. Br J Ophthalmol 2009; 93:742-6.
  9. Mohan K, Sharma A, Pandav SS. Unilateral lateral rectus muscle recession and medial rectus muscle resection with or without advancement for postoperative consecutive exotropia. J AAPOS 2006; 10:220–24.
  10. Parks MM, Bloom JN. The “slipped” muscle. Ophthalmology 1979; 86:1389-96.
  11. Ludwig IH, Chow AC. Scar remodeling after strabismus surgery. J AAPOS 2000; 4:326-33.
  12. Chen SI, Knox PC, Hiscott P, Marsh IB. Detection of the slipped extraocular muscle after strabismus surgery. Ophthalmology 2005; 112:686-93. 
  13. Apt L, Isenberg SJ. The oculocardiac reflex as a surgical aid in identifying a slipped or “lost” extraocular muscle. Br J Ophthalmol 1980; 64:362-5.
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Neha Singh, Vinita SinghConsecutive Exotropia: A Case Report and Review of Literature.DJO 2018;29:51-53
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Neha Singh, Vinita SinghConsecutive Exotropia: A Case Report and Review of Literature.DJO [serial online] 2018[cited 2018 Dec 13];29:51-53. Available from: http://www.djo.org.in/articles/29/2/Consecutive-Exotropia.html
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