Intermittent exotropia is usually classified according to

A comparison of ocular alignment success of hang-back versus conventional bilateral lateral rectus muscle recession for true divergence excess intermittent exotropia Kanwar Mohan, MS, a and Ashok Sharma, MS b PURPOSE METHODS RESULTS CONCLUSIONS To assess whether hang-back or conventional bilateral lateral rectus muscle recessions were more successful in achieving a satisfactory postoperative ocular alignment in patients with true divergence excess intermittent exotropia. The medical records of consecutive patients with true divergence excess intermittent exotropia who underwent bilateral lateral rectus muscle recession using hang-back or conventional techniques were retrospectively analyzed. All surgeries were performed by a single surgeon using the same standard table of surgical dosage. We compared the preoperative characteristics and motor surgical outcomes between the two groups. Success was defined as alignment within 10 D of intermittent exotropias at distance and near. Any amount of postoperative esotropia was considered a failure. A total of 42 patients were included: 13 in the hang-back group and 29 in the conventional group. The mean age at surgery, mean preoperative deviation at near and distance, mean amount of lateral rectus muscle recession, and mean follow-up duration were not statistically significantly different between groups. At the most recent follow-up, the conventional group had a significantly greater success rate (#10 D of intermittent exotropia) than the hang-back group (83% vs 31%, P 5 0.0009). There was no statistically significant difference in the mean amount of lateral rectus recession between patients with successful and unsuccessful surgical outcomes in both groups. Within the limitations of this study, conventional bilateral lateral rectus recessions were more effective than hang-back recessions in achieving a successful postoperative alignment in patients with true divergence excess intermittent exotropia. ( J AAPOS 2013;17:29-33) Intermittent exotropia is usually classified according to patterns of exodeviation at distance and near fixation. True divergence excess intermittent exotropia refers to those deviations that remain greater at distance than at near after remeasurement at near either through 13.0 D spherical lenses 1 or after a period of monocular occlusion. 2-8 Burian and Franceschetti 8 found a true divergence excess pattern in only 4% of the patients with exodeviations. In patients with intermittent exodeviation greater at distance than at near fixation, von Noorden 5 found true divergence excess pattern in only 30%. Several authors have reported on the surgical treatment of intermittent exotropia, including the divergence excess type. 7,9-11 Most surgeons agree that bilateral lateral rectus muscle recession should be performed for true divergence excess type of intermittent exotropia. 9,10,12-14 Both conventional and hang-back techniques have been used for recession of the lateral rectus muscles for treating intermittent or constant exotropia. 7,9-11,15-19 There are a few studies that compare the surgical results of hang-back with those of conventional bilateral lateral rectus muscle recession for exotropia in general. 15-17 To our knowledge, such a comparison has not been made for true divergence excess intermittent exotropia. This study aims to present a comparison of our motor results with hang-back to those with conventional bilateral lateral rectus muscle recession for treating true divergence excess intermittent exotropia. Author affiliations: a Squint Centre, and b Cornea Centre, Chandigarh, India Submitted May 15, 2012. Revision accepted September 27, 2012. Published online January 25, 2013. Correspondence: Kanwar Mohan, MS, Squint Centre, SCO: 833-834 (2nd Floor), Sector 22-A, Chandigarh- 160022, India (email: kanwarmohan@sify.com). Copyright Ó 2013 by the American Association for Pediatric Ophthalmology and Strabismus. 1091-8531/$36.00 http://dx.doi.org/10.1016/j.jaapos.2012.09.014 Subjects and Methods The records of consecutive patients with true divergence excess intermittent exotropia who underwent bilateral lateral rectus muscle recessions between 1994 and 2010 by a single surgeon (KM) at the Squint Centre, Chandigarh, India, were retrospectively reviewed. The study was approved by the Squint Centre Institutional Review Board and complied with the tenets 29

30 Mohan and Sharma Volume 17 Number 1 / February 2013 Table 1. Comparison of preoperative characteristics and surgical outcomes between the hang-back and conventional recession groups Hang-back (n 5 13) Conventional (n 5 29) P value Mean age at surgery, years (range) 9.8 7.0 (3-24) 11.7 7.4 (4-24) 0.44 a Mean preoperative deviation, PD (range) Near 18.2 10.4 (10-40) 13.4 7.7 (0-30) 0.10 a Distance 35.4 10.3 (25-55) 34.6 9.1 (20-55) 0.79 a Mean (range) amount of LR recession, each eye, mm 7.5 1.4 (5.5-10.0) 7.5 1.4 (5.0-10.0) 0.90 a Mean postoperative follow-up, months (range) 21.1 22.5 (6-60) 18.3 10.4 (6-45) 0.59 a Surgical result 4 (30.8%) 24 (82.8%) 0.0009 b Success N (%) #10 PD X (T) LR, lateral rectus recession; PD, prism diopters; X(T), intermittent exotropia. a By t test. b By Z test for proportions. of the Declaration of Helsinki. We performed hang-back recession surgery between 1994 and 2002 and conventional recession surgery between 2003 and 2010. Patients with previous strabismus surgery and a postoperative follow-up \6 months were excluded. We diagnosed a true divergence excess intermittent exotropia if the deviation was $15 D greater at distance than at near fixation after 24 hours of monocular occlusion. All baseline and postoperative follow-up examinations were performed by one unmasked author. Ocular deviations were measured at near and distance in all patients with the use of alternate prism and cover test. The deviation measurement at distance was performed while the patient fixated on a letter in the line corresponding to his or her distance visual acuity on the Snellen chart at 6 meters. We did not include outdoor targets. The AC/A ratio was not determined. Visual acuity was recorded with a Snellen distance visual acuity chart. Amblyopia was defined as a difference of 2 or more Snellen lines between the best-corrected visual acuity of the two eyes. All patients underwent symmetrical bilateral lateral rectus muscle recessions for the largest exotropic deviation. The amount of surgery was based on the same standard table of surgical dosage in both groups. 13 In conventional recession surgery, the lateral rectus muscle was attached directly at the desired scleral site, whereas in the hang-back recession surgery, the lateral rectus muscle was suspended from the original insertion to the desired scleral attachment site with a double-armed 6-0 polyglactin 910 suture. Any associated overaction of the superior or inferior oblique muscles was treated with a weakening procedure for the corresponding oblique muscles. Surgical success was defined as alignment within 10 D of intermittent exotropia at distance and near fixation at the most recent follow-up examination. Any amount of postoperative esotropia at the most recent examination was considered a failure. Data were analyzed using the t test and the Z test for proportions. Results were also compared with Kaplan-Meier survival analysis and the log-rank test. A P value of \0.05 was considered statistically significant. Results A total of 42 patients (26 females [62%]) met inclusion criteria. Of these, 13 underwent bilateral hang-back recessions and 29 conventional recessions of the lateral rectus muscles. A comparison of preoperative characteristics between the hang-back and conventional groups is provided in Table 1. One patient (7.69%) in the hang-back group and none of the patients in the conventional group had amblyopia. None of the patients in either group had superior oblique overaction. The hang-back group included 3 bilateral inferior oblique muscle recessions; the conventional group, 3 unilateral and 1 bilateral inferior oblique muscle recessions for associated inferior oblique muscle overactions. No statistically significant differences between the 2 surgical groups were found for the mean age at surgery, mean preoperative deviations at near and distance, mean amount of lateral rectus recession, and mean follow-up duration (Table 1). At the most recent follow-up, the success rate in the hang-back group was 31%, whereas the success rate in the conventional group was 83%, and this difference was statistically significant (P 5 0.0009, 95% CI for difference of proportions, 0.20-0.72; Table 1). The log-rank test also showed that the conventional group had a significantly greater success rate than the hang-back group (P 5 0.022). Kaplan-Meier survival analysis demonstrated that the cumulative probability of success according to time after surgery was 67% in the hang-back recession group and 97% in the conventional group at 1 year, and 33% in the hang-back group and 73% in the conventional group at 3 years follow-up (Figure 1). Of the 42 patients, 28 had a successful outcome. Of these, 19 (68%) had orthophoria and 9 (32%) intermittent exotropia #10 D. None of the patients in the hang-back group or the conventional group exhibited induced vertical deviation. At the most recent follow-up, 7 of the 14 patients with unsuccessful outcome in the hang-back group exhibited a mean distant intermittent exotropia of 19.4 D 5.50 D (range, 12 D -30 D ) and 2 had a mean distance esotropia of 5.5 D 0.71 D (range, 5 D -6 D ), whereas all 5 patients with unsuccessful outcome in the conventional group had a mean distance intermittent exotropia of 16.0 D 2.83 D (range, 14 D -20 D ). There was no significant difference in the mean distance intermittent exotropia between the two groups (P 5 0.134). The final distance intermittent exodeviation was not more than the preoperative deviation in any patient. Overall, patients with unsuccessful outcome had a final distance intermittent exotropia of \20 D (7 patients), 20 D (4 patients) and 30 D (1 patient), and a distance

Volume 17 Number 1 / February 2013 Mohan and Sharma 31 FIG 1. Cumulative probability of success according to time after surgery in hang-back versus conventional recession groups. esotropia of\10 D (2 patients). None of the patients with an unsuccessful result elected to pursue further strabismus surgery. Of the patients with unsuccessful outcomes, all 9 in the hang-back group had a mean lateral rectus recession of 7.83 1.48 mm (range, 5.5-10.0 mm) and all 5 in the conventional group had a mean recession of 7.90 1.67 mm (range, 5.0-9.0 mm). In patients in the hang-back group who had a successful outcome, the mean amount of lateral rectus muscle recession was 6.63 0.95 mm (range, 6.0-8.0 mm), compared with 7.83 1.48 mm (range, 5.5-10.0 mm) in those with an unsuccessful surgical result; this difference was not statistically significant (P 5 0.166). In the conventional group, the mean amount of lateral rectus recession was 7.44 1.33 mm (range, 5.5-10.0 mm) in patients with a successful outcome, compared to 7.90 1.67 mm (range, 5.0-9.0 mm) in those with an unsuccessful outcome; this difference was likewise not statistically significant (P 5 0.503). Discussion Although Hardesty and colleagues 9 relied on a 5 D difference between the distance and near measurement for differentiating between true divergence excess and pseudodivergence excess types of intermittent exotropia, most authors 8,10,12,20-22 use a 10 D difference. We chose a 15 D value, as von Noorden 5,23 and Zibrandtsen and colleagues. 24 Patients with divergence excess intermittent exotropia have a strong fusion mechanism at near. To differentiate between true and pseudodivergence excess patterns, length of diagnostic occlusion varies, from 5 days, 2 to 3 days, 3 24 hours, 4 1 hour, 5-7 and even 30-45 minutes. 8 We used 24 hours of occlusion because we believed that a relatively prolonged period of occlusion would eliminate fusional convergence effectively and would bring out the true deviation at near. Some studies on comparison of hang-back with conventional bilateral lateral rectus recession for exotropia have not found any significant difference in the surgical success rates (#10 D of deviation) between the two techniques. 16,17 However, Capo and colleagues 15 found a significantly greater success rate (#8 D of deviation) in the conventional group than in the hang-back group (85% vs 64%) in their patients with intermittent or constant exotropia. They attributed this difference mainly to late overcorrections in the hang-back group, possibly due to posterior bowing of the lateral rectus muscle. To our knowledge, the present study is the first to compare surgical success rates between the conventional and hang-back bilateral lateral rectus recessions specifically for true divergence excess intermittent exotropia. Several investigators 25,26 have reported that some patients with intermittent exotropia have an even larger angle of deviation if fixation is carried out on a far distant outdoor target, and relying on such a measurement improves results. We used a Snellen line at a distance of 6 meters and not an outdoor target for distant fixation; thus it is possible that some of our patients had an even more deviation at distance, requiring a greater amount of lateral rectus recession. However, we believe that this would not affect our comparative results between the two surgical groups because patients in both groups had a distance deviation measurement while fixating at the same type of target at the same distance. Although the surgical success rates of both groups decreased as followup progressed, the conventional group still had a greater success rate than the hang-back group. In this study, most of the patients with an unsuccessful result in both surgical groups had an intermittent exotropia at their last follow-up. Postoperative undercorrections have been explained as a creeping forward of the extraocular muscles following recession procedures: several animal studies have shown a forward migration of the rectus muscles recessed with both conventional and hang-back techniques. 27-30 Climenhaga and Pearce 27 found no significant difference in postoperative muscle migration between the conventional and hang-back recession groups. On the other hand, Ohtsuki and colleauges 30 found a significantly greater mean forward creep with hang-back recession than that with conventional recession (1.81 vs 0.83 mm). Several clinical studies have reported on the site of reattachment of the extraocular muscles following hang-back recession. Repka and colleagues 28 reoperated a few undercorrected patients following hang-back recession and found the extraocular muscles to be attached at the intended site. Mills and colleagues 31 found a 2 mm forward migration of the rectus muscle on re-exploring an undercorrected patient 2 years after a 5 mm hang-back recession. Although none of our patients with undercorrection was re-explored, it is possible that the lateral rectus muscle crept forward along the surface of the globe and attached more anteriorly during the healing phase. We do not

32 Mohan and Sharma Volume 17 Number 1 / February 2013 know whether a creeping forward response is specific to the divergence excess type or whether it occurs in other types as well. Further study on this point is needed. Because there were no significant differences in the mean preoperative deviation and the mean amount of lateral rectus recession in the two surgical groups, we can offer no explanation for the greater success rate in the conventional group other than less postoperative forward migration. Postoperative muscle migration occurs more frequently after large recessions. The lateral rectus muscle, because of its greater wrap-around effect, does not take up slack like other muscles and is theoretically more likely than other muscles to creep forward with big hang-back recessions. The predictability of muscle reattachment to the globe after larger than 7 mm of hang-back recession remains controversial. 32 Although all patients with an unsuccessful outcome in both the hang-back and conventional groups had undergone a mean lateral rectus recession.7 mm, we did not find a significant difference in the mean amount of lateral rectus recession between patients with successful and unsuccessful surgical results in both groups. Some patients with divergence excess type intermittent exotropia have a high AC/A ratio, which masks the true near deviation. 5,21,22 Such patients have a risk of developing consecutive esotropia at near following exotropia surgery. 33 Therefore, either surgery should be avoided and optical management should be recommended in these patients or they should be advised about this risk. 33 We did not measure the AC/A ratio in our patients. Our study is limited by its retrospective and nonrandomized nature and by the relatively small number of subjects in the hang-back group. In addition, all pre- and postoperative measurements were taken by a single unmasked observer and were therefore susceptible to bias. As it was a sequential study, with hang-back recessions performed first and conventional recessions later, the possibility exists of an improvement in the surgeon s skills. However, both hang-back and conventional recessions had been performed for several years before the patients in this study were operated on. Hence it is unlikely that the improved surgical skills contributed to the higher success rate in the conventional group. Literature Search A literature search was performed on PubMed using the following terms: divergence excess exotropia, true divergence excess exotropia, and hang-back recession. Acknowledgments We thank Dr. Suresh Sharma, Department of Statistics, Punjab University, Chandigarh, for performing the statistical analysis of this study. References 1. Brown HW. Aids in the diagnosis of strabismus, in strabismus. Symposium of the New Orleans Academy of Ophthalmology. St. Louis: Mosby-Year Book, Inc; 1962. 231. 2. Niedercker O, Scott WE. The value of diagnostic occlusion for intermittent exotropia. Am Orthopt J 1975;25:90-91. 3. Gr af M, Rost D, Kaufman H. Results of combined divergence operation in intermittent exotropia in 120 children [in German]. Klin Monatsbl Augenheilkd 2001;218:31-7. 4. Scobee RG. Exophoria. In: The ocurotatory muscles. St. Louis, MO: CV Mosby Co; 1952. 171. 5. von Noorden GK. Divergence excess and simulated divergence excess: diagnosis and surgical management. Ophthalmologica 1969; 26:719-28. 6. G url u VP, Erda N. Diagnostic occlusion test in intermittent exotropia. J AAPOS 2008;12:504-6. 7. Chia A, Seenyen L, Long QB. Surgical experience with two muscle surgery for the treatment of intermittent exotropia. J AAPOS 2006; 10:206-11. 8. Burian HM, Franceschetti AT. Evaluation of diagnostic methods for the classification of exodeviations. Trans Am Ophthalmol Soc 1970; 68:56-71. 9. Hardesty HH, Boynton JR, Keenan P. Treatment of intermittent exotropia. Arch Ophthalmol 1978;96:268-74. 10. Kushner BJ. Selective surgery for intermittent exotropia based on distance/near differences. Arch Ophthalmol 1998;116:324-8. 11. Celebi S, K ukner AS. Large bilateral lateral rectus recession in large angle divergence excess exotropia. Eur J Ophthalmol 2001;11:6-8. 12. Burian HM. Exodeviations: their classification, diagnosis and treatment. Am J Ophthalmol 1966;62:1161-6. 13. Burke MJ. Intermittent exotropia. In: Nelson LB, Wagner RS, eds. International Ophthalmology Clinics. Vol 25, No. 4. Boston: Little, Brown; 1985:53-68. 14. Thorburn D, Koklanis K, Georgievski Z. Management of intermittent exotropia strabismus of the divergence excess type. Binocul Vis Strabismus Q 2010;25:243-52. 15. Capo H, Repka MX, Guyton DL. Hang-back lateral rectus recessions for exotropia. J Pediatr Ophthalmol Strabismus 1989;26:31-4. 16. Orlin A, Mills M, Ying GS, Liu C. A comparison of hang-back with conventional recession surgery for exotropia. J AAPOS 2007;11: 597-600. 17. Rajavi Z, Ghadim HM, Nikkhoo M, Dehsarvi B. Comparison of hang-back and conventional recession surgery for horizontal strabismus. J Pediatr Ophthalmol Strabismus 2001;38:273-7. 18. Rodrigues AC, Nelson LB. Long-term results of hang-back lateral rectus recession. J Pediatr Ophthalmol Strabismus 2006;43:161-4. 19. Mohan K, Ram J, Sharma A. Comparison between adjustable and non-adjustable hang-back muscle recession for concomitant exotropia. Indian J Ophthalmol 1998;46:21-4. 20. Burian HM, Spivey BE. The surgical management of exodeviation. Trans Am Ophthalmol Soc 1964;62:276-305. 21. Lim Z, Seenyen L, Quah BL. Characteristics of divergence excess type of intermittent exotropia in Asian children. J AAPOS 2011;15: 468-72. 22. Le T, Koklanis K, Georgievski Z. The fixation target influences the near deviation and AC/A ratio in intermittent exotropia. J AAPOS 2010;14:25-30. 23. von Noorden GK. Binocular Vision and Ocular Motility: Theory and Management of Strabismus. 5th ed. St. Louis: Mosby; 1996. 342. 24. Zibrandtsen P, Rindziunski E, Gregersen E. Ten years follow-up of surgery for intermittent exotropia. Acta Ophthalmol 1986;64:374-8. 25. Burian HM, Smith DR. Comparative measurement of exodeviations at twenty and one hundred feet. Trans Am Ophthalmol Soc 1971; 69:188-99. 26. Kushner BJ. The distance angle to target in surgery for intermittent exotropia. Arch Ophthalmol 1998;116:189-94. 27. Climenhaga HW, Pearce WG. Adjustable sutures: Experimental assessment of final muscle position. Can J Ophthalmol 1984;19: 234-6. 28. Repka MX, Fishman PJ, Guyton DL. The site of reattachment of the extraocular muscle following hang-back recession. J Pediatr Ophthalmol Strabismus 1990;27:286-90.

Volume 17 Number 1 / February 2013 Mohan and Sharma 33 29. Lang RM, Pearce WG. Extraocular muscle recession with a suture loop in dogs. Can J Ophthalmol 1981;16:27-9. 30. Ohtsuki H, Oshima K, Hasebe S, Kobashi R, Okano M, Furuse T. Extraocular muscle surgery in a rabbit model: site of reattachment following hang-back and conventional recession. Graefes Arch Clin Exp Ophthalmol 1994;232: 689-94. 31. Mills PV, Hyper TJ, Duff GR. Loop recession of the recti muscles. Eye 1987;1:593-6. 32. Potter WS, Nelson LB, Handa JT. Hemihang-back recession: description of the technique and review of the literature. Ophthalmic Surgery 1990;21:711-15. 33. Kushner BJ, Morton GV. Distance/near differences in intermittent exotropia. Arch Ophthalmol 1998;116:478-86. When patients with anisohyperopia (eg, 11.00 OD and 14.00 OS) come in for their yearly dilated examination and ask how long their eyes will be blurry from the drops, suggest that, only for the remainder of the day, they wear their glasses upside down to read. I love the surprised look on their faces (and the faces of the parents) when they try it and see that it works! Dr. Maury A. Marmor, MD, Long Island, New York