- Email: [email protected]
Risk factors for consecutive exotropia after vertical rectus transposition for esotropic Duane retraction syndrome
Risk factors for consecutive exotropia after vertical rectus transposition for esotropic Duane retraction syndrome Federico G. Velez, MD, Jessica K. Laursen, MD, and Stacy L. Pineles, MD PURPOSE METHODS
RESULTS
CONCLUSIONS
To define risk factors for postoperative exotropia after vertical rectus transposition (VRT) for Duane syndrome. The records of patients with Duane syndrome who underwent augmented VRT were retrospectively reviewed; those with postoperative exotropia (study group) were compared with those with postoperative esotropia/orthotropia (controls). A total of 51 patients were included, of whom 14 were exotropic postoperatively. Of the 14, 6 became exotropic after augmented VRT, and 8 who were initially esotropic became exotropic after subsequent medial rectus muscle (MR) recession. Study subjects were significantly younger (2 2 years vs 6 10 years, P 5 0.04) and demonstrated less restriction on intraoperative forced duction testing than control subjects. Subjects who became exotropic after MR muscle recession had significantly less esotropia at near (5.2D 6.5D vs 18.4 D 7.9D esotropia, respectively; P 5 0.005) and in adduction (1D 2D exotropia vs 3D 4D esotropia, respectively; P 5 0.02) than control patients who also underwent VRT and MR muscle recession. Forced duction testing was also significantly different among these groups (P 5 0.03). Risk factors for exotropia after augmented VRT include younger age and less restriction on forced duction testing. Additional risk factors for exotropia after VRT and subsequent MR muscle recession include preoperative exotropia in adduction and smaller deviation at near. These factors may be useful in distinguishing patients at risk, allowing for consideration of less powerful procedures. ( J AAPOS 2011;15:326-330)
E
sotropic Duane syndrome is characterized by anomalous lateral rectus innervation from branches of the oculomotor nerve, resulting in subnormal (or absent) abducting force, esotropia (ET), torticollis, and co-contraction. In its most typical form, Duane syndrome is unilateral and is characterized by a total lack of abducting ability. Various surgical techniques have been described that address the esotropia and torticollis associated with this disorder.1-5 Augmented vertical rectus muscle transposition (VRT) has been proposed as a means by which to not only improve strabismus and torticollis but also to increase abducting rotations.4,5 However, in improving abducting rotations, there is a risk of postoperative overcorrection resulting in exotropia (XT).6,7 Postoperative exodeviations in this population are poorly tolerated because they may create Author affiliations: Jules Stein Eye Institute and Department of Ophthalmology, University of California, Los Angeles, California Submitted January 10, 2011. Revision accepted May 8, 2011. Reprint requests: Stacy L. Pineles, MD, Jules Stein Eye Institute, 100 Stein Plaza, David Geffen School of Medicine at UCLA, Los Angles, CA 90095-7002 (email: [email protected]. edu). Copyright Ó 2011 by the American Association for Pediatric Ophthalmology and Strabismus. 1091-8531/$36.00 doi:10.1016/j.jaapos.2011.05.006
326
a narrowing of the diplopia-free field and a reversal of torticollis. Because augmented VRT has been commonly performed at our center for esotropic Duane syndrome for more than 10 years, we aimed to evaluate postoperative overcorrections in these patients and, in addition, to define associations with postoperative overcorrection that may be identified preoperatively and used to guide surgical planning and patient counseling.
Methods This study was approved by the University of California, Los Angeles Institutional Review Board and conformed to the requirements of the United States Health Insurance Portability and Accountability Act. The clinical records of all patients in a single-surgeon practice (Arthur L. Rosenbaum, MD) between 1998 and 2008 with the diagnosis of esotropic Duane syndrome were retrospectively reviewed. Subjects who underwent full tendon VRT with posterior fixation (augmented VRT) as their first surgical procedure and had at least 8 weeks of postoperative follow-up were included in the analysis. The technique used for this procedure is published elsewhere.8 Patients with a history of previous strabismus surgery before their VRT, bilateral Duane syndrome, or missing data related to deviation measurements in adduction or abduction, ocular rotations, or intraoperative forced
Journal of AAPOS
Volume 15 Number 4 / August 2011 duction testing were excluded. In addition, patients who underwent nonaugmented or partial transpositions were excluded. Subjects were divided into 2 groups: those who were esotropic or orthotropic at the final follow-up visit (control group) and those who were exotropic at the final follow-up visit (study group). The following pre- and postoperative characteristics were recorded from the patients’ medical record: age at onset, age at surgery, preoperative motor alignment at distance and near and in the cardinal positions of gaze, degrees of torticollis, an assessment of ocular ductions, and intraoperative forced duction testing. For those subjects who underwent additional surgical procedures after the VRT, these characteristics were also recorded at the preoperative visit before the subsequent surgeries. Surgical information recorded included the results of intraoperative forced duction testing and all subsequent surgical procedures. Visual acuity was assessed by the use of projected ageappropriate optotypes after a manifest or cycloplegic refraction. Ocular alignment was assessed with cover/uncover and prism and alternate cover testing at distance (20 feet) in the cardinal gaze positions. Motor alignment at near was assessed at 14 inches. All motor evaluations were performed with spectacle correction. Torticollis was estimated by the same experienced strabismologist in the patient’s habitual head position in degrees. Torticollis was assessed with the subject viewing a distant target. Ocular ductions were measured using a standard 4-point scale.9 Intraoperative forced duction testing was graded on a 3-point scale (mild, moderate, severe) by the operating surgeon. Statistical analyses were performed with STATA version 10.0 (StataCorp LP, College Station, TX) and Microsoft Excel (Microsoft Corp, Redmond, WA). To assess the difference between those subjects who became exotropic after VRT and those who did not, a t test was used to directly compare the mean characteristics of both groups. A P value \0.05 was considered statistically significant. The Fisher exact test was used to assess the association between subsequent medial rectus (MR) muscle recession and an exotropic outcome. To compare the results of forced duction testing, a c2 test was used. Comparisons were made between mean values for all subjects in the exotropic and control groups as well as in subgroups of subjects who had VRT only or VRT and subsequent MR muscle recession.
Results During the study period, 59 patients with unilateral esotropic Duane syndrome underwent augmented VRT surgery as the primary surgical treatment. A total of 51 patients met the inclusion criteria. Of these, 14 were exotropic at the final office visit, and 37 were orthotropic or esotropic (controls). Of the 51 patients, 25 underwent subsequent MR muscle recession. Of these 25, 8 were part of the exotropic group and 17 were part of the control group. Direct comparison among overall outcome groups is summarized in Table 1. The patients ranged in age from 6 months to 34 years (median age, 2 years). The mean amount of postoperative esotropia was 9 8D in the control group. Within the control group, those patients who eventually underwent subsequent MR muscle reces-
Journal of AAPOS
Velez, Laursen, and Pineles
327
sion had significantly more preoperative esotropia in primary position, in adduction, and at near than those esotropic control subjects undergoing only a VRT procedure (21D 8D ET vs 13D 5D ET, 3D 4D ET vs 2D 4D XT, and 18D 8D ET vs 10D 6D ET, respectively; P \ 0.01 for all comparisons). In addition, the postoperative follow-up length was significantly longer in the VRT-only control group than in the esotropic control group who underwent subsequent MR muscle recession (25 30 months vs 17 16 months, respectively). The mean amount of postoperative exotropia in the study group was 8D 4D (range, 4D-14D). Overall, the exotropic group had a younger age at surgery (2 2 years vs 6 10 years, respectively; P 5 0.04) and a trend toward less restriction on intraoperative forced duction testing (P 5 0.07). For all patients undergoing VRT with or without MR muscle recession, the mean decrease in adduction postoperatively was 0.6 0.7. A Fisher exact test revealed that undergoing a MR muscle recession was not significantly associated with an increased risk of postoperative exotropia at the final follow-up visit (P 5 0.5). Of the subjects whose only surgical procedure was VRT, 6 were exotropic at the last postoperative visit and 20 were esotropic or orthotropic. There was no significant difference between groups in any preoperative characteristics. The mean time to presentation with exotropia was 5 4 years (range, 1 day to 10 years). Two patients were exotropic on postoperative day one. The mean postoperative deviation in primary position was 9D 4D exotropia in the exotropic group and 3D 3D esotropia in the control group at distance (P 5 0.002), and 7D 9D exotropia and 1D 3D esotropia at near (P 5 0.07), respectively. In the study group, the torticollis reversed to the other direction at 4 7 , whereas there was residual torticollis in the same direction at 3 3 in the control group (P 5 0.08). The change in adducting rotations was 1.2 0.8 in the study group and 0.1 0.1 in the control group (P 5 0.03). Taken together, for all patients undergoing VRT only (exotropic and control group combined), there was no statistically significant decrease in adduction ( 0.1 0.2 preoperatively vs 0.3 0.5 postoperatively). There was no significant difference in limitation to abduction postoperatively. Of the subjects who underwent subsequent MR recession for residual esotropia after VRT, 8 were exotropic and 17 were esotropic or orthotropic. Direct comparison among groups is summarized in Table 2. The mean time to presentation with exotropa was 1 1.2 years after the MR recession (range, 1 day to 3 years). Three patients were exotropic on postoperative day one. Preoperative characteristics that were significantly different among exotropic and control subjects included preoperative deviation in adduction (0.8D 2D XT vs 3D 4D ET, respectively; P 5 0.02), preoperative deviation at near (5D 6D ET vs 18D 8D ET, respectively; P 5 0.005), and results of intraoperative forced duction testing (exotropic patients had less restriction to abduction; P 5 0.03). The mean
328
Velez, Laursen, and Pineles
Volume 15 Number 4 / August 2011
Table 1. Comparison of preoperative characteristics of all patients undergoing vertical rectus muscle transposition for esotropic Duane syndrome
Age Subsequent medial rectus muscle recession Preoperative distance esotropia Preoperative near esotropia Preoperative torticollis Preoperative adduction Preoperative abduction Intraoperative forced duction test
Postoperative follow-Up
Exotropic subjects (n 5 14) mean SD
Control subjectsa (n 5 37) mean SD
2 2 years n 5 8 (57%) 15D 10D 12D 11D 16 10 0.2 0.4 3.5 0.6 No restriction n 5 0 Mild n 5 3 Moderate n 5 8 Severe n 5 3
6 10 years n 5 20 (54%) 17D 7D 14D ET 16 5 0.1 0.2 3.9 0.4 No restriction n 5 1 Mild n 5 5 Moderate n 5 18 Severe n 5 11
0.04 0.5c 0.7 0.7 0.9 0.8 0.2 0.07d
59 44 months
18 24 months
0.07
P valueb
ET, esotropia; SD, standard deviation. Control subjects include all patients who were esotropic or orthotropic at the final follow-up visit. b Two-tailed paired t test for all comparisons except as otherwise noted. c Fisher exact test. d 2 c test. a
Table 2. Comparison of preoperative characteristics of patients undergoing vertical rectus transposition and then subsequent medial rectus recession for esotropic Duane syndrome
Age Preoperative distance deviation Preoperative near deviation Preoperative deviation in adduction Preoperative torticollis Preoperative adduction Preoperative abduction Intraoperative forced duction test
Postoperative follow-up
Exotropic subjects (n 5 8): mean SD
Control subjectsa (n 5 17): mean SD
2.9 2.6 years 18 5D ET 5 6 ET 0.8 2 XT 16 4 0.06 0.2 4 0.3 No restriction n 5 0 Mild n 5 3 Moderate n 5 5 Severe n 5 0
8.5 10 years 21D 8D ET 18 8 ET 3 4 ET 16 5 0.2 0.2 3.8 0.4 No restriction n 5 0 Mild n 5 1 Moderate n 5 6 Severe n 5 8
46 43 months
17 16 months
P valueb 0.07 0.2 0.005c 0.02c 0.99 0.2 0.09 0.03c,d
0.1
ET, esotropia; SD, standard deviation; XT, exotropia. Control subjects include all patients who were esotropic or orthotropic at the final follow-up visit. b Two-tailed paired t test for all comparisons. c Statistically significant. d 2 c test. a
postoperative deviation in primary position was 7D 3D in the exotropic group and 16D 6D in the esotropia group at distance (P \ 0.001), and 5D 5D and 2D 5D at near (P 5 0.006), respectively. In the exotropic group, the torticollis reversed to the other direction at 6 4 , whereas there was residual torticollis 0.3 2 in the same direction in the control group (P 5 0.007). There was a trend toward more limitation to adduction in the exotropic group (change of 1.3 0.8 vs 0.7 0.7; P 5 0.08). Taken together, for all patients undergoing VRT and subsequent MR muscle recession (exotropic and control group combined), there was a statistically significant decrease in adduction ( 0.1 0.2 preoperatively vs 1 0.8 postoperatively, P \ 0.001).
Discussion Although few other surgical options exist in Duane syndrome to enlarge the diplopia-free binocular visual field and improve abduction, VRT is not without complications.4,8 In this study, we evaluated the occurrence of postoperative exotropia in a series of patients undergoing VRT procedures. The results suggest that there are several associations with this particular outcome that can be determined preoperatively and used to guide surgical decision making and patient counseling. In general, patients of a younger age and those with less restriction to abduction during intraoperative forced duction testing were more likely to demonstrate exotropia at
Journal of AAPOS
Volume 15 Number 4 / August 2011 their final postoperative visit. Patients of a younger age are less likely to have an acquired restrictive force in the MR muscle that may occur in patients with a more longstanding esotropia. For this reason, they may have a greater chance of a postoperative overcorrection because of less stiffness in the MR muscle than their older counterparts. It is also quite possible, however, that the younger mean age of the study subjects is confounded by other unknown age-related factors. In addition, those patients in whom forced duction testing revealed less MR muscle stiffness may be at greater risk for postoperative exotropia because of an increase in the passive abducting forces after VRT. In this series, the amount of esotropia preoperatively did not appear to influence the overall likelihood of an overcorrection except in the subgroup of patients who underwent subsequent MR muscle recession. In these cases, there was a significantly increased risk of postoperative exotropia in those patients with smaller deviations at near and in adduction. The likely explanation for this finding is that these subjects were more likely to have either some degree of anomalous lateral rectus muscle innervation (more co-contraction), better baseline abducting rotation ability, or a larger effect from the transposition, and the adducting force from the MR muscle was likely preventing a postVRT overcorrection. However, after the MR muscle recession, the balance of forces was “tipped” into the exotropic direction. Theoretically, in Duane patients in whom the amount of lateral rectus muscle innervation is close to that of the MR muscle, there is a risk that increasing the vector force toward abduction (by performing VRT and/or subsequent MR muscle recession) can result in exotropia. In our series, those patients whose subsequent MR muscle recession resulted in a final postoperative overcorrection were more likely to have less esotropia (or more exotropia) in adduction, which likely represents more co-contraction. Exotropia can also be a complication of more commonly performed procedures for esotropic Duane syndrome like unilateral or bilateral MR muscle recession.10-12 In patients with any amount of anomalous lateral rectus muscle activity, an ipsilateral MR muscle weakening procedure places the patient at risk for postoperative exotropia. Less than full adduction or any amount of exotropia in adduction may be important preoperative predictors of secondary exotropia in these cases.11 In addition, a contralateral MR muscle weakening procedure may cause sufficient fixation duress in the Duane eye to create an exodeviation.13 Case reports of consecutive exotropia after MR muscle recession have been theorized to result from unrecognized preoperative limited adducting rotations, an unrecognized accommodative component, or a “slipped” MR muscle.11,12 In 3 of the largest series of MR recession for esotropic Duane syndrome, consecutive exotropia was present in 0 of 7,3 1 of 26,14 and 0 of 25 patients.1 Although our rate of consecutive exotropia is greater, the loss of adduction experienced by our subjects overall (including all study and control subjects) was 0.6 0.7, which is better than the overall experience in
Journal of AAPOS
Velez, Laursen, and Pineles
329
the above referenced reports, in which the mean decreases in adduction ranged between 0.9 0.814 and 1.1 0.6.3 Although very few of the subjects in these studies experienced a consecutive exotropia, measurements of the deviation in adduction or at near were not included consistently in the results; in addition, the sample sizes of patients with unilateral esotropic Duane syndrome were relatively small. Although our results demonstrated a greater incidence of postoperative exotropia, functional outcomes such as diplopia-free binocular visual field, amount of residual or reverse torticollis, and long-term stability cannot be readily compared among studies. In addition, we believe that our overall rate of consecutive exotropia is artificially high due to our exclusion criteria, which resulted in the elimination of 8 additional patients, all of whom had only a VRT and none of whom were exotropic at the final follow-up visit. The results of this study should be understood within the context of its limitations. First, this was a retrospective study in which the surgical procedure may not have been completely standardized over time. The retrospective nature of the study precludes definitive conclusions regarding surgical indications and contraindications given that it is subject to inherent selection and follow-up bias. Specifically, the mean postoperative follow-up interval in the exotropic study group was longer than that of controls; therefore it is possible that some of the “control” patients may develop exotropia at a future date. In addition, postoperative forced duction testing was not performed on many patients and would have been useful in determining postoperative mechanical restrictions. Finally, there may have been bias in the grading of forced duction testing restriction and orthoptic measurements by the surgeon over time. Despite its limitations, this study represents the largest series of Duane patients undergoing VRT describing overcorrection after surgery. The results suggest that younger patients and those without restriction to abduction are at increased risk of postoperative exotropia. Surgeons should approach these cases with increased caution and should counsel patients regarding the possibility of postoperative overcorrection. However, we do not wish to imply that VRT is contraindicated in this patient subgroup because the results can be excellent and similar complications are possible with the remaining surgical options, including simple MR muscle recessions.
Acknowledgments We thank the late Dr. Arthur L. Rosenbaum for providing the patients for this study and for years of thoughtful discussions that led to its design. References 1. Farvardin M, Rad AH, Ashrafzadeh A. Results of bilateral medial rectus muscle recession in unilateral esotropic Duane syndrome. J AAPOS 2009;13:339-42. 2. Gobin MH. Surgical management of Duane’s syndrome. Br J Ophthalmol 1974;58:301-6. 3. Pressman SH, Scott WE. Surgical treatment of Duane’s syndrome. Ophthalmology 1986;93:29-38.
330
Velez, Laursen, and Pineles
4. Rosenbaum AL. Costenbader Lecture. The efficacy of rectus muscle transposition surgery in esotropic Duane syndrome and VI nerve palsy. J AAPOS 2004;8:409-19. 5. Velez FG, Foster RS, Rosenbaum AL. Vertical rectus muscle augmented transposition in Duane syndrome. J AAPOS 2001;5:105-13. 6. Kushner BJ. A case of residual exotropia after revision of a modified Hummelsheim procedure for Duane’s syndrome. Binocul Vision Q 1992;7:70. 7. Souza-Dias C. Congenital VI nerve palsy is Duane’s syndrome until disproven. Binocul Vis Q 1992;7:70. 8. Ruth AL, Velez FG, Rosenbaum AL. Management of vertical deviations after vertical rectus transposition surgery. J AAPOS 2009;13:16-9. 9. Mehta A. Chief complaint, history, and physical examination. In: Rosenbaum AL, Santiago P, eds. Clinical strabismus management. Philadelphia, PA: W.B. Saunders; 1999:3-21.
Volume 15 Number 4 / August 2011 10. Greenberg MF, Pollard ZF. Poor results after recession of both medial rectus muscles in unilateral small-angle Duane’s syndrome, type I. J AAPOS 2003;7:142-5. 11. Kushner BJ, Arthur BW, Mazow ML, Medow NB, Young TL. Grand rounds #51: A case of consecutive exotropia after medial rectus recession for Duane syndrome. Binocul Vis Strabismus Q 1998;13: 188-92. 12. Nelson LB. Severe adduction deficiency following a large medial rectus recession in Duane’s retraction syndrome. Arch Ophthalmol 1986; 104:859-62. 13. Jampolsky AL. Duane Syndrome. In: Rosenbaum AL, Santiago P, eds. Clinical strabismus management. Philadelphia, PA: W.B. Saunders; 1999:325-46. 14. Barbe ME, Scott WE, Kutschke PJ. A simplified approach to the treatment of Duane’s syndrome. Br J Ophthalmol 2004;88:131-8.
Journal of AAPOS
RESULTS
CONCLUSIONS
To define risk factors for postoperative exotropia after vertical rectus transposition (VRT) for Duane syndrome. The records of patients with Duane syndrome who underwent augmented VRT were retrospectively reviewed; those with postoperative exotropia (study group) were compared with those with postoperative esotropia/orthotropia (controls). A total of 51 patients were included, of whom 14 were exotropic postoperatively. Of the 14, 6 became exotropic after augmented VRT, and 8 who were initially esotropic became exotropic after subsequent medial rectus muscle (MR) recession. Study subjects were significantly younger (2 2 years vs 6 10 years, P 5 0.04) and demonstrated less restriction on intraoperative forced duction testing than control subjects. Subjects who became exotropic after MR muscle recession had significantly less esotropia at near (5.2D 6.5D vs 18.4 D 7.9D esotropia, respectively; P 5 0.005) and in adduction (1D 2D exotropia vs 3D 4D esotropia, respectively; P 5 0.02) than control patients who also underwent VRT and MR muscle recession. Forced duction testing was also significantly different among these groups (P 5 0.03). Risk factors for exotropia after augmented VRT include younger age and less restriction on forced duction testing. Additional risk factors for exotropia after VRT and subsequent MR muscle recession include preoperative exotropia in adduction and smaller deviation at near. These factors may be useful in distinguishing patients at risk, allowing for consideration of less powerful procedures. ( J AAPOS 2011;15:326-330)
E
sotropic Duane syndrome is characterized by anomalous lateral rectus innervation from branches of the oculomotor nerve, resulting in subnormal (or absent) abducting force, esotropia (ET), torticollis, and co-contraction. In its most typical form, Duane syndrome is unilateral and is characterized by a total lack of abducting ability. Various surgical techniques have been described that address the esotropia and torticollis associated with this disorder.1-5 Augmented vertical rectus muscle transposition (VRT) has been proposed as a means by which to not only improve strabismus and torticollis but also to increase abducting rotations.4,5 However, in improving abducting rotations, there is a risk of postoperative overcorrection resulting in exotropia (XT).6,7 Postoperative exodeviations in this population are poorly tolerated because they may create Author affiliations: Jules Stein Eye Institute and Department of Ophthalmology, University of California, Los Angeles, California Submitted January 10, 2011. Revision accepted May 8, 2011. Reprint requests: Stacy L. Pineles, MD, Jules Stein Eye Institute, 100 Stein Plaza, David Geffen School of Medicine at UCLA, Los Angles, CA 90095-7002 (email: [email protected]. edu). Copyright Ó 2011 by the American Association for Pediatric Ophthalmology and Strabismus. 1091-8531/$36.00 doi:10.1016/j.jaapos.2011.05.006
326
a narrowing of the diplopia-free field and a reversal of torticollis. Because augmented VRT has been commonly performed at our center for esotropic Duane syndrome for more than 10 years, we aimed to evaluate postoperative overcorrections in these patients and, in addition, to define associations with postoperative overcorrection that may be identified preoperatively and used to guide surgical planning and patient counseling.
Methods This study was approved by the University of California, Los Angeles Institutional Review Board and conformed to the requirements of the United States Health Insurance Portability and Accountability Act. The clinical records of all patients in a single-surgeon practice (Arthur L. Rosenbaum, MD) between 1998 and 2008 with the diagnosis of esotropic Duane syndrome were retrospectively reviewed. Subjects who underwent full tendon VRT with posterior fixation (augmented VRT) as their first surgical procedure and had at least 8 weeks of postoperative follow-up were included in the analysis. The technique used for this procedure is published elsewhere.8 Patients with a history of previous strabismus surgery before their VRT, bilateral Duane syndrome, or missing data related to deviation measurements in adduction or abduction, ocular rotations, or intraoperative forced
Journal of AAPOS
Volume 15 Number 4 / August 2011 duction testing were excluded. In addition, patients who underwent nonaugmented or partial transpositions were excluded. Subjects were divided into 2 groups: those who were esotropic or orthotropic at the final follow-up visit (control group) and those who were exotropic at the final follow-up visit (study group). The following pre- and postoperative characteristics were recorded from the patients’ medical record: age at onset, age at surgery, preoperative motor alignment at distance and near and in the cardinal positions of gaze, degrees of torticollis, an assessment of ocular ductions, and intraoperative forced duction testing. For those subjects who underwent additional surgical procedures after the VRT, these characteristics were also recorded at the preoperative visit before the subsequent surgeries. Surgical information recorded included the results of intraoperative forced duction testing and all subsequent surgical procedures. Visual acuity was assessed by the use of projected ageappropriate optotypes after a manifest or cycloplegic refraction. Ocular alignment was assessed with cover/uncover and prism and alternate cover testing at distance (20 feet) in the cardinal gaze positions. Motor alignment at near was assessed at 14 inches. All motor evaluations were performed with spectacle correction. Torticollis was estimated by the same experienced strabismologist in the patient’s habitual head position in degrees. Torticollis was assessed with the subject viewing a distant target. Ocular ductions were measured using a standard 4-point scale.9 Intraoperative forced duction testing was graded on a 3-point scale (mild, moderate, severe) by the operating surgeon. Statistical analyses were performed with STATA version 10.0 (StataCorp LP, College Station, TX) and Microsoft Excel (Microsoft Corp, Redmond, WA). To assess the difference between those subjects who became exotropic after VRT and those who did not, a t test was used to directly compare the mean characteristics of both groups. A P value \0.05 was considered statistically significant. The Fisher exact test was used to assess the association between subsequent medial rectus (MR) muscle recession and an exotropic outcome. To compare the results of forced duction testing, a c2 test was used. Comparisons were made between mean values for all subjects in the exotropic and control groups as well as in subgroups of subjects who had VRT only or VRT and subsequent MR muscle recession.
Results During the study period, 59 patients with unilateral esotropic Duane syndrome underwent augmented VRT surgery as the primary surgical treatment. A total of 51 patients met the inclusion criteria. Of these, 14 were exotropic at the final office visit, and 37 were orthotropic or esotropic (controls). Of the 51 patients, 25 underwent subsequent MR muscle recession. Of these 25, 8 were part of the exotropic group and 17 were part of the control group. Direct comparison among overall outcome groups is summarized in Table 1. The patients ranged in age from 6 months to 34 years (median age, 2 years). The mean amount of postoperative esotropia was 9 8D in the control group. Within the control group, those patients who eventually underwent subsequent MR muscle reces-
Journal of AAPOS
Velez, Laursen, and Pineles
327
sion had significantly more preoperative esotropia in primary position, in adduction, and at near than those esotropic control subjects undergoing only a VRT procedure (21D 8D ET vs 13D 5D ET, 3D 4D ET vs 2D 4D XT, and 18D 8D ET vs 10D 6D ET, respectively; P \ 0.01 for all comparisons). In addition, the postoperative follow-up length was significantly longer in the VRT-only control group than in the esotropic control group who underwent subsequent MR muscle recession (25 30 months vs 17 16 months, respectively). The mean amount of postoperative exotropia in the study group was 8D 4D (range, 4D-14D). Overall, the exotropic group had a younger age at surgery (2 2 years vs 6 10 years, respectively; P 5 0.04) and a trend toward less restriction on intraoperative forced duction testing (P 5 0.07). For all patients undergoing VRT with or without MR muscle recession, the mean decrease in adduction postoperatively was 0.6 0.7. A Fisher exact test revealed that undergoing a MR muscle recession was not significantly associated with an increased risk of postoperative exotropia at the final follow-up visit (P 5 0.5). Of the subjects whose only surgical procedure was VRT, 6 were exotropic at the last postoperative visit and 20 were esotropic or orthotropic. There was no significant difference between groups in any preoperative characteristics. The mean time to presentation with exotropia was 5 4 years (range, 1 day to 10 years). Two patients were exotropic on postoperative day one. The mean postoperative deviation in primary position was 9D 4D exotropia in the exotropic group and 3D 3D esotropia in the control group at distance (P 5 0.002), and 7D 9D exotropia and 1D 3D esotropia at near (P 5 0.07), respectively. In the study group, the torticollis reversed to the other direction at 4 7 , whereas there was residual torticollis in the same direction at 3 3 in the control group (P 5 0.08). The change in adducting rotations was 1.2 0.8 in the study group and 0.1 0.1 in the control group (P 5 0.03). Taken together, for all patients undergoing VRT only (exotropic and control group combined), there was no statistically significant decrease in adduction ( 0.1 0.2 preoperatively vs 0.3 0.5 postoperatively). There was no significant difference in limitation to abduction postoperatively. Of the subjects who underwent subsequent MR recession for residual esotropia after VRT, 8 were exotropic and 17 were esotropic or orthotropic. Direct comparison among groups is summarized in Table 2. The mean time to presentation with exotropa was 1 1.2 years after the MR recession (range, 1 day to 3 years). Three patients were exotropic on postoperative day one. Preoperative characteristics that were significantly different among exotropic and control subjects included preoperative deviation in adduction (0.8D 2D XT vs 3D 4D ET, respectively; P 5 0.02), preoperative deviation at near (5D 6D ET vs 18D 8D ET, respectively; P 5 0.005), and results of intraoperative forced duction testing (exotropic patients had less restriction to abduction; P 5 0.03). The mean
328
Velez, Laursen, and Pineles
Volume 15 Number 4 / August 2011
Table 1. Comparison of preoperative characteristics of all patients undergoing vertical rectus muscle transposition for esotropic Duane syndrome
Age Subsequent medial rectus muscle recession Preoperative distance esotropia Preoperative near esotropia Preoperative torticollis Preoperative adduction Preoperative abduction Intraoperative forced duction test
Postoperative follow-Up
Exotropic subjects (n 5 14) mean SD
Control subjectsa (n 5 37) mean SD
2 2 years n 5 8 (57%) 15D 10D 12D 11D 16 10 0.2 0.4 3.5 0.6 No restriction n 5 0 Mild n 5 3 Moderate n 5 8 Severe n 5 3
6 10 years n 5 20 (54%) 17D 7D 14D ET 16 5 0.1 0.2 3.9 0.4 No restriction n 5 1 Mild n 5 5 Moderate n 5 18 Severe n 5 11
0.04 0.5c 0.7 0.7 0.9 0.8 0.2 0.07d
59 44 months
18 24 months
0.07
P valueb
ET, esotropia; SD, standard deviation. Control subjects include all patients who were esotropic or orthotropic at the final follow-up visit. b Two-tailed paired t test for all comparisons except as otherwise noted. c Fisher exact test. d 2 c test. a
Table 2. Comparison of preoperative characteristics of patients undergoing vertical rectus transposition and then subsequent medial rectus recession for esotropic Duane syndrome
Age Preoperative distance deviation Preoperative near deviation Preoperative deviation in adduction Preoperative torticollis Preoperative adduction Preoperative abduction Intraoperative forced duction test
Postoperative follow-up
Exotropic subjects (n 5 8): mean SD
Control subjectsa (n 5 17): mean SD
2.9 2.6 years 18 5D ET 5 6 ET 0.8 2 XT 16 4 0.06 0.2 4 0.3 No restriction n 5 0 Mild n 5 3 Moderate n 5 5 Severe n 5 0
8.5 10 years 21D 8D ET 18 8 ET 3 4 ET 16 5 0.2 0.2 3.8 0.4 No restriction n 5 0 Mild n 5 1 Moderate n 5 6 Severe n 5 8
46 43 months
17 16 months
P valueb 0.07 0.2 0.005c 0.02c 0.99 0.2 0.09 0.03c,d
0.1
ET, esotropia; SD, standard deviation; XT, exotropia. Control subjects include all patients who were esotropic or orthotropic at the final follow-up visit. b Two-tailed paired t test for all comparisons. c Statistically significant. d 2 c test. a
postoperative deviation in primary position was 7D 3D in the exotropic group and 16D 6D in the esotropia group at distance (P \ 0.001), and 5D 5D and 2D 5D at near (P 5 0.006), respectively. In the exotropic group, the torticollis reversed to the other direction at 6 4 , whereas there was residual torticollis 0.3 2 in the same direction in the control group (P 5 0.007). There was a trend toward more limitation to adduction in the exotropic group (change of 1.3 0.8 vs 0.7 0.7; P 5 0.08). Taken together, for all patients undergoing VRT and subsequent MR muscle recession (exotropic and control group combined), there was a statistically significant decrease in adduction ( 0.1 0.2 preoperatively vs 1 0.8 postoperatively, P \ 0.001).
Discussion Although few other surgical options exist in Duane syndrome to enlarge the diplopia-free binocular visual field and improve abduction, VRT is not without complications.4,8 In this study, we evaluated the occurrence of postoperative exotropia in a series of patients undergoing VRT procedures. The results suggest that there are several associations with this particular outcome that can be determined preoperatively and used to guide surgical decision making and patient counseling. In general, patients of a younger age and those with less restriction to abduction during intraoperative forced duction testing were more likely to demonstrate exotropia at
Journal of AAPOS
Volume 15 Number 4 / August 2011 their final postoperative visit. Patients of a younger age are less likely to have an acquired restrictive force in the MR muscle that may occur in patients with a more longstanding esotropia. For this reason, they may have a greater chance of a postoperative overcorrection because of less stiffness in the MR muscle than their older counterparts. It is also quite possible, however, that the younger mean age of the study subjects is confounded by other unknown age-related factors. In addition, those patients in whom forced duction testing revealed less MR muscle stiffness may be at greater risk for postoperative exotropia because of an increase in the passive abducting forces after VRT. In this series, the amount of esotropia preoperatively did not appear to influence the overall likelihood of an overcorrection except in the subgroup of patients who underwent subsequent MR muscle recession. In these cases, there was a significantly increased risk of postoperative exotropia in those patients with smaller deviations at near and in adduction. The likely explanation for this finding is that these subjects were more likely to have either some degree of anomalous lateral rectus muscle innervation (more co-contraction), better baseline abducting rotation ability, or a larger effect from the transposition, and the adducting force from the MR muscle was likely preventing a postVRT overcorrection. However, after the MR muscle recession, the balance of forces was “tipped” into the exotropic direction. Theoretically, in Duane patients in whom the amount of lateral rectus muscle innervation is close to that of the MR muscle, there is a risk that increasing the vector force toward abduction (by performing VRT and/or subsequent MR muscle recession) can result in exotropia. In our series, those patients whose subsequent MR muscle recession resulted in a final postoperative overcorrection were more likely to have less esotropia (or more exotropia) in adduction, which likely represents more co-contraction. Exotropia can also be a complication of more commonly performed procedures for esotropic Duane syndrome like unilateral or bilateral MR muscle recession.10-12 In patients with any amount of anomalous lateral rectus muscle activity, an ipsilateral MR muscle weakening procedure places the patient at risk for postoperative exotropia. Less than full adduction or any amount of exotropia in adduction may be important preoperative predictors of secondary exotropia in these cases.11 In addition, a contralateral MR muscle weakening procedure may cause sufficient fixation duress in the Duane eye to create an exodeviation.13 Case reports of consecutive exotropia after MR muscle recession have been theorized to result from unrecognized preoperative limited adducting rotations, an unrecognized accommodative component, or a “slipped” MR muscle.11,12 In 3 of the largest series of MR recession for esotropic Duane syndrome, consecutive exotropia was present in 0 of 7,3 1 of 26,14 and 0 of 25 patients.1 Although our rate of consecutive exotropia is greater, the loss of adduction experienced by our subjects overall (including all study and control subjects) was 0.6 0.7, which is better than the overall experience in
Journal of AAPOS
Velez, Laursen, and Pineles
329
the above referenced reports, in which the mean decreases in adduction ranged between 0.9 0.814 and 1.1 0.6.3 Although very few of the subjects in these studies experienced a consecutive exotropia, measurements of the deviation in adduction or at near were not included consistently in the results; in addition, the sample sizes of patients with unilateral esotropic Duane syndrome were relatively small. Although our results demonstrated a greater incidence of postoperative exotropia, functional outcomes such as diplopia-free binocular visual field, amount of residual or reverse torticollis, and long-term stability cannot be readily compared among studies. In addition, we believe that our overall rate of consecutive exotropia is artificially high due to our exclusion criteria, which resulted in the elimination of 8 additional patients, all of whom had only a VRT and none of whom were exotropic at the final follow-up visit. The results of this study should be understood within the context of its limitations. First, this was a retrospective study in which the surgical procedure may not have been completely standardized over time. The retrospective nature of the study precludes definitive conclusions regarding surgical indications and contraindications given that it is subject to inherent selection and follow-up bias. Specifically, the mean postoperative follow-up interval in the exotropic study group was longer than that of controls; therefore it is possible that some of the “control” patients may develop exotropia at a future date. In addition, postoperative forced duction testing was not performed on many patients and would have been useful in determining postoperative mechanical restrictions. Finally, there may have been bias in the grading of forced duction testing restriction and orthoptic measurements by the surgeon over time. Despite its limitations, this study represents the largest series of Duane patients undergoing VRT describing overcorrection after surgery. The results suggest that younger patients and those without restriction to abduction are at increased risk of postoperative exotropia. Surgeons should approach these cases with increased caution and should counsel patients regarding the possibility of postoperative overcorrection. However, we do not wish to imply that VRT is contraindicated in this patient subgroup because the results can be excellent and similar complications are possible with the remaining surgical options, including simple MR muscle recessions.
Acknowledgments We thank the late Dr. Arthur L. Rosenbaum for providing the patients for this study and for years of thoughtful discussions that led to its design. References 1. Farvardin M, Rad AH, Ashrafzadeh A. Results of bilateral medial rectus muscle recession in unilateral esotropic Duane syndrome. J AAPOS 2009;13:339-42. 2. Gobin MH. Surgical management of Duane’s syndrome. Br J Ophthalmol 1974;58:301-6. 3. Pressman SH, Scott WE. Surgical treatment of Duane’s syndrome. Ophthalmology 1986;93:29-38.
330
Velez, Laursen, and Pineles
4. Rosenbaum AL. Costenbader Lecture. The efficacy of rectus muscle transposition surgery in esotropic Duane syndrome and VI nerve palsy. J AAPOS 2004;8:409-19. 5. Velez FG, Foster RS, Rosenbaum AL. Vertical rectus muscle augmented transposition in Duane syndrome. J AAPOS 2001;5:105-13. 6. Kushner BJ. A case of residual exotropia after revision of a modified Hummelsheim procedure for Duane’s syndrome. Binocul Vision Q 1992;7:70. 7. Souza-Dias C. Congenital VI nerve palsy is Duane’s syndrome until disproven. Binocul Vis Q 1992;7:70. 8. Ruth AL, Velez FG, Rosenbaum AL. Management of vertical deviations after vertical rectus transposition surgery. J AAPOS 2009;13:16-9. 9. Mehta A. Chief complaint, history, and physical examination. In: Rosenbaum AL, Santiago P, eds. Clinical strabismus management. Philadelphia, PA: W.B. Saunders; 1999:3-21.
Volume 15 Number 4 / August 2011 10. Greenberg MF, Pollard ZF. Poor results after recession of both medial rectus muscles in unilateral small-angle Duane’s syndrome, type I. J AAPOS 2003;7:142-5. 11. Kushner BJ, Arthur BW, Mazow ML, Medow NB, Young TL. Grand rounds #51: A case of consecutive exotropia after medial rectus recession for Duane syndrome. Binocul Vis Strabismus Q 1998;13: 188-92. 12. Nelson LB. Severe adduction deficiency following a large medial rectus recession in Duane’s retraction syndrome. Arch Ophthalmol 1986; 104:859-62. 13. Jampolsky AL. Duane Syndrome. In: Rosenbaum AL, Santiago P, eds. Clinical strabismus management. Philadelphia, PA: W.B. Saunders; 1999:325-46. 14. Barbe ME, Scott WE, Kutschke PJ. A simplified approach to the treatment of Duane’s syndrome. Br J Ophthalmol 2004;88:131-8.
Journal of AAPOS