Classic treatment for exotropia is bilateral lateral rectus recession or recession of the lateral rectus muscle along with resection of the ipsilateral medial rectus muscle. A similar process for esotropia is usually either a bilateral recession or a recession and resection. Unilateral rectus muscle surgery has been reported in the literature1–28 and many of these studies show that this procedure is safe and equally effective in small to moderate deviations. However, many surgeons do not perform this surgery because of a concern of incomitance and undercorrection.
This review focuses on current literature on unilateral strabismus surgery for small to moderate angle esotropia, exotropia, undercorrected or recurrent strabismus, and convergence or divergence insufficiency.
Unilateral Recession for Exotropia
Early articles reporting unilateral lateral rectus recession for exotropia may have suffered from recessions that were too small and/or a lack of uniformity in the amount of recession for a specific exotropia.1 For example, in 1950 Lee and O'Brien2 reported unfavorable results for single lateral rectus muscle recession in patients with various amounts of exotropia but they made no attempt to uniformly recess a lateral rectus muscle for a specific amount of exotropia. In 1964, Dunlap and Gaffney3 showed that unilateral lateral rectus surgery was adequate only in cases of a small amount of exotropia of 10 to 15 prism diopters (PD), but preoperative deviations and the amount of muscle recessed were not reported.
Favorable results have been found in more recent studies (Table 1). Nelson et al.4 reported promising results in patients with moderate angle exotropia of 15 to 20 PD who were surgically treated with a unilateral lateral rectus recession of 7, 7.5, or 8 mm (7 mm for 15 to 16 PD, 7.5 mm for 17 to 18 PD, and 8 mm for 20 PD). In fact, 94% of the patients were within 8 PD of orthophoria at a mean follow-up of 13.9 months postoperatively. This was the first study that provided surgical guidelines for unilateral lateral rectus recession in exotropia. Subsequently, Weakley and Stager5 and Olitsky6 also provided surgical guidelines for unilateral lateral rectus recession in intermittent or constant exotropia.
Unilateral Rectus Muscle Recession for Exotropia and Esotropia
Weakley and Stager5 performed a study on unilateral lateral rectus recession up to 10 mm for exotropia and up to 40 PD in both children and adults. Thirty-three of 45 patients (73%) were satisfactorily aligned with a minimum follow-up of 6 months. The authors found less of an effect from this procedure in patients older than 4 years compared with those younger than 4 years (89% vs 61%, respectively), and concluded that unilateral lateral rectus recessions from 7 to 9.5 mm were useful and relatively successful. They determined the procedure had an advantage over bilateral lateral rectus recession because only one eye underwent surgery and there was a virtual absence of overcorrections.
Deutsch et al.7 reported that all 30 patients with moderate exotropia of 15 to 20 PD treated with unilateral lateral rectus recession of 7 or 7.5 mm for deviations of 15 or 18 PD, respectively, improved postoperatively to orthotropia (77%), small angle exophoria (13%), or small angle esotropia (10%). Dadeya and Kamlesh8 evaluated 27 patients with exotropia who underwent a unilateral lateral rectus recession of 8 mm for a moderate deviation of 25 to 30 PD. After a 3-year follow-up, 77% of their patients showed a satisfactory alignment of ±5 PD of orthophoria. Also of note, they did not observe any incomitance.
Spierer and Ben-Simon9 described the surgical results of 25 patients who underwent unilateral lateral rectus recession for moderate angle exotropia and compared them with 38 patients who underwent bilateral lateral rectus recession for the treatment of exotropia. The success rate of patients with a deviation of less than 10 PD was 84% and 74%, respectively. No incomitance was observed in the unilateral group. Menon et al.10 concluded that unilateral and bilateral rectus recession are equally effective in intermittent exotropia ranging from 15 to 25 PD. Wang and Nelson11 reported on 100 children with small to moderate angle exotropia with a minimum follow-up of 6 months. Successful alignment was achieved in 99% and 76% of patients preoperatively and 6 months of follow-up, respectively.
Unilateral Recession for Esotropia
Several investigators have evaluated recessing only one medial rectus muscle for treatment of small to moderate angle esotropia. (Table 1). Unilateral muscle recessions were reported in the literature as early as 1951.12 In 1957, Kaiser13 reported “definite improvement” in a series of 12 adult cases of esotropia corrected by unilateral medial rectus recession. In 1970, Chamberlain14 reported 100 cases of unilateral medial rectus recession of 3.5 to 4 mm and concluded that it was a reasonable operation for non-accommodative esodeviation measuring less than 20 PD. Pediatric ophthalmologists were hesitant to do surgery at this time because the results were so poor, but this was because the amount of recession was relatively small. However, Grin and Nelson15 achieved an 80% success rate in patients with a moderate angle of 30 to 35 PD treated with unilateral medial rectus recession of 6 or 6.5 mm. Pollard and Manley16 had a series of 10 patients who underwent 5-mm recession of one medial rectus muscle, with a 90% success rate. Their conclusion was that one-muscle surgery is appropriate in small angle esotropia.
Zak's17 series of 53 patients with 14 to 20 PD of esotropia had a 100% success rate after one 6-mm recession at the 2-year mean follow-up. Procianoy and Justo18 described 25 patients with high accomodative convergence/accommodation ratios and esotropia of 4 to 12 PD at distance and 15 to 35 PD at near treated with a 6- to 8-mm unilateral medial rectus recession on the esotropic eye, according to the near deviation. They used a 6-mm recession for 20 PD, 7-mm for 20 to 30 PD, and 8-mm for 30 to 35 PD. In 24 patients (96%), the esodeviation was less than 10 PD, with a follow-up ranging from 3 to 7 years. The only complication was a slight widening of the eyelid fissure in 7 patients who required a 7- or 8-mm recession. They concluded that unilateral medial rectus recession is an effective method in the treatment of esotropia with high accommodative convergence/accomodation ratios.
Stack et al.19 compared the results of a range of medial rectus recessions, both unilateral and bilateral, performed by one surgeon. They found that at long-term follow-up the equivalent change in deviation achieved per millimeter was smaller than that observed for bilateral recessions. The authors concluded that unilateral medial rectus recession is appropriate for esotropias less than 25 PD.
Cogen and Roberts20 reviewed 56 patients who had graded unilateral surgery of 6- to 8-mm medial rectus recession for esoptropia of 15 to 40 PD (mean: 25.8 PD) at distance and 18 to 45 PD (mean: 30.7 PD) at near. They had an 86% success rate, defined as residual esotropia of less than 8 PD at the most recent postoperative visit with a minimum of 5 months and an average of 32 months of postoperative follow-up. The authors concluded that unilateral supramaximal medial rectus recession appears to be a safe and effective treatment for medium angle non-accommodative esotropia.
Wang and Nelson21 reported an outcome study of 123 patients treated by graded unilateral medial rectus recession for small to moderate angle esotropia with a minimum follow-up of 6 months. The eyes of 96.8% of the patients were successfully aligned (±5 PD of orthophoria in primary and lateral gaze) at 6 months of follow-up. The study not only showed the success of the graded unilateral lateral medial rectus recession, but provided surgical guidelines for the treatment of small to moderate angle esotropia.
Unilateral Rectus Resection for Undercorrected or Recurrent Strabismus
Surgery for undercorrected or recurrent strabismus may be challenging. In these cases, one-muscle surgery can be an option (Table 2). Olitsky et al.22 described 60 patients who underwent a unilateral re-section of the lateral rectus muscle and 21 who underwent a unilateral resection of the medial rectus muscle. Acceptable eye alignment at the 6-month postoperative examination was reached by 90% and 95.2% in patients undergoing a unilateral lateral rectus resection and medial rectus resection, respectively.
Unilateral Rectus Muscle Resection for Exotropia and Esotropia
Nucci et al.23 concluded that resection of a single lateral rectus muscle with the surgical dosage calculated by doubling the angle of strabismus and applying the recommended surgical dosage to one lateral rectus muscle is a treatment option for patients with small angle residual esotropia following bilateral medial rectus muscle recession. Unilateral medial rectus muscle resection in patients with recurrent exotropia has been reported as a useful and effective surgical method.24,25
Yang and Hwang26 retrospectively compared outcomes after bilateral and unilateral medial rectus resection in patients with recurrent exotropia of 25 PD or less at distance after bilateral lateral rectus recession. One-muscle resection was performed by taking half of the value of bilateral medial rectus muscle resection up to a maximum of 10 mm. They found that the incidence of successful outcome and recurrence at last follow-up were not significantly different between the two groups, but bilateral medial rectus resection showed a significantly higher rate of overcorrection in the early and late postoperative periods.
Divergence and Convergence Insufficiency
Divergence insufficiency esotropia (or acquired comitant esotropia) is at least 10 PD larger at distance than at near. Treatment involves either bilateral lateral rectus resection or, more recently reported, unilateral lateral rectus resection. De Decker and Baenge27 showed that unilateral medial rectus resection is useful in convergence insufficiency and in related small angle exotropia or deviations not exceeding 7°. Hoover and Giangiacomo28 eliminated divergence in 5 of 6 patients with a 5.5- to 8-mm unilateral lateral rectus resection. Medial rectus recessions have also been advocated. Thomas29 advocated unilateral medial rectus recession in deviations of 17 PD or less and bilateral surgery in larger deviations.
The use of unilateral rectus muscle surgery has been controversial. This procedure has not been widely accepted nor studied. Many surgeons avoided using this technique because of concerns that it may result in a significant number of undercorrections and/or produce ocular incomitance. Studies have shown that unilateral rectus muscle recession or resection is a safe, effective, and predictable treatment for small to moderate angle horizontal deviations and even larger deviations. One-muscle surgery has the clear advantages of requiring less surgical and anesthesia time, having fewer risks of complications (eg, perforation and endophthalmitis), and leaving other muscles untouched for repeat surgery. For these reasons, one-muscle surgery should be considered an alternative approach to bilateral surgery. In addition, one-muscle surgery should be considered for patients with a history of previous strabismus surgery.
Postoperative lateral incomitance has been rarely reported. However, surgeons should always be aware of the risk of incomitance in asymmetric surgery. The poor outcomes described in the literature that resulted from unilateral surgery may have resulted from performing too small of a recession or resection for a specific amount of deviation. Although unilateral rectus muscle surgery has been shown to be a successful procedure for ocular misalignment, prospective, randomized studies with larger samples can provide more definite conclusions.
- Wang L, Nelson LB. Reassessment of unilateral rectus surgery for horizontal strabismus. Yearbook of Ophthalmology. 2009;163–168.
- Lee OS, O'Brien CS. Surgical treatment of concomitant divergent strabismus. In: Allen JH, ed. Strabismus Ophthalmic Symposium. St. Louis, MO: CV Mosby; 1950:395–400.
- Dunlap EA, Gaffney RB. Surgical management of intermittent exotropia. American Orthoptic Journal. 1964;13:20–33. doi:10.1080/0065955X.1964.11981410 [CrossRef]
- Nelson LB, Bacal DA, Burke MJ. An alternative approach to the surgical management of exotropia: the unilateral lateral rectus recession. J Pediatr Ophthalmol Strabismus. 1992;29:357–360.
- Weakley DR Jr, Stager DR. Unilateral lateral rectus recession in exotropia. Ophthalmic Surg. 1993;24:458–460.
- Olitsky SE. Early and late postoperative alignment following unilateral lateral rectus recession for intermittent exotropia. J Pediatr Ophthalmol Strabismus. 1998;35:146–148.
- Deutsch JA, Nelson LB, Sheppard RW, Burke MJ. Unilateral lateral rectus recession for the treatment of exotropia. Ann Ophthalmol. 1992;24:111–113.
- Dadeya S, Kamlesh. Long-term results of unilateral lateral rectus recession in intermittent exotropia. J Pediatr Ophthalmol Strabismus. 2003;40:283–287.
- Spierer A, Ben-Simon GJ. Unilateral and bilateral lateral rectus recession in exotropia. Ophthalmic Surg Lasers Imaging. 2005;36:114–117.
- Menon V, Singla MA, Saxena R, Phulijele S. Comparative study of unilateral and bilateral surgery in moderate exotropia. J Pediatr Ophthalmol Strabismus. 2010;47:288–291. doi:10.3928/01913913-20091118-07 [CrossRef]
- Wang L, Nelson LB. Outcome study of unilateral lateral rectus recession for small to moderate angle intermittent exotropia in children. J Pediatr Ophthalmol Strabismus. 2010;47:242–247. doi:10.3928/01913913-20091019-12 [CrossRef]
- Stine GT. The surgical treatment of esophoria. Am J Ophthalmol. 1951;34:1307–1313. doi:10.1016/0002-9394(51)91868-5 [CrossRef]
- Kaiser RF. Surgery for esophoria in the adult. Am Orthop J. 1957;7:107–108. doi:10.1080/0065955X.1957.11981209 [CrossRef]
- Chamberlain W. The single medial rectus recession operation. J Pediatr Ophthalmol Strabismus. 1970;7:208–211.
- Grin TR, Nelson LB. Large unilateral medial rectus recession for the treatment of esotropia. Br J Ophthalmol. 1987;71:377–379. doi:10.1136/bjo.71.5.377 [CrossRef]
- Pollard ZF, Manley D. Unilateral medial rectus recession for small-angle esotropia. Arch Ophthalmol. 1976;94:780–781. doi:10.1001/archopht.1976.03910030384006 [CrossRef]
- Zak TA. Results of large single medial rectus recession. J Pediatr Ophthalmol Strabismus. 1986;23:17–21.
- Procianoy E, Justo DM. Results of unilateral medial rectus recession in high AC/A ratio esotropia. J Pediatr Ophthalmol Strabismus. 1991;28:212–214.
- Stack RR, Burley CD, Bedggood A, Elder MJ. Unilateral versus bilateral medial rectus recession. J AAPOS. 2003;7:263–267. doi:10.1016/S1091-8531(03)00117-4 [CrossRef]
- Cogen MS, Roberts BW. Graded unilateral supramaximal medial rectus recession for moderate angle esotropia. Binocul Vis Strabismus Q. 2006;21:147–153.
- Wang L, Nelson LB. Outcome study of graded unilateral medial rectus recession for small to moderate angle esotropia. J Pediatr Ophthalmol Strabismus. 2011;48:20–24. doi:10.3928/01913913-20100818-05 [CrossRef]
- Olitsky SE, Kelly C, Lee H, Nelson LB. Unilateral rectus resection in the treatment of undercorrected or recurrent strabismus. J Pediatr Ophthalmol Strabismus. 2001;38:349–353.
- Nucci P, Serafino M, Trivedi RH, Saunders RA. One-muscle surgery in small-angle residual esotropia. J AAPOS. 2007;11:269–272. doi:10.1016/j.jaapos.2006.10.020 [CrossRef]
- Mims JL 3rd, . Outcome of 5 mm resection of one medial rectus extraocular muscle for recurrent exotropia. Binocul Vis Strabismus Q. 2003;18:143–150.
- Chae SH, Chun BY, Kwon JY. The effect of unilateral medial rectus muscle resection in patient with recurrent exotropia. Korean J Ophthalmol. 2008;22:174–177. doi:10.3341/kjo.2008.22.3.174 [CrossRef]
- Yang HK, Hwang JM. Bilateral vs unilateral medial rectus resection for recurrent exotropia after bilateral lateral rectus recession. Am J Ophthalmol. 2009;148:459–465. doi:10.1016/j.ajo.2009.04.017 [CrossRef]
- de Decker W, Baenge JJ. Unilateral medial rectus resection in the treatment of small-angle exodeviation. Graefes Arch Clin Exp Ophthalmol. 1988;226:161–164. doi:10.1007/BF02173308 [CrossRef]
- Hoover DL, Giangiacomo J. Results of a single lateral rectus re-section for divergence and partial sixth nerve paralysis. J Pediatr Ophthalmol Strabismus. 1993;30:124–126.
- Thomas AH. Divergence insufficiency. J AAPOS. 2000;4:359–361. doi:10.1067/mpa.2000.111783 [CrossRef]
Unilateral Rectus Muscle Recession for Exotropia and Esotropia
|Study||No. of Patients||Preoperative Deviation (PD)||Amount of Recession (mm)||Success Rate (%)|
| Nelson et al.4||55||15 to 20||7 to 8||51|
| Weakley & Stager5||45||10 to 40||6 to 10||73|
| Olitsky6||35||15 to 25||7 to 9||77|
| Deutsch et al.7||30||15 to 20||7 to 7.5||77|
| Dadeya & Kamlesh8||27||25 to 30||8||78|
| Spierer & Ben-Simon9||25||7 to 25||6 to 9||84|
| Wang & Nelson11||100||15 to 35||7 to 10||76|
| Grin & Nelson15||16||30 to 35 (N)||6 to 6.5||80|
| Zak17||53||14 to 20 (N)||6||100|
| Procianoy & Justo18||25||15 to 35 (N)||6 to 8||96|
| Stack et al.19||45||10 to 45 (D)||5 to 8||82|
| Cogen & Roberts20||56||15 to 40 (D)
18 to 45 (N)||6 to 8||86|
| Wang & Nelson21||123||15 to 35 (N)||5 to 7||96.8|
Unilateral Rectus Muscle Resection for Exotropia and Esotropia
|Study||No. of Patients||Preoperative Deviation (PD)||Amount of Resection (mm)||Success Rate (%)|
| Olitsky et al.22||21||16 to 25||5 to 6.5||95.2|
| Yang & Hwang26||20||14 to 25||7 to 10||80|
| Olitsky et al.22||60||14 to 25||7 to 9||90|
| Nucci et al.23||17||15 to 20||6 to 7||100|