- Email: [email protected]
Binocular Status After Surgery for Constant and Intermittent Exotropia
Binocular Status After Surgery for Constant and Intermittent Exotropia HAIXIANG WU, MD, JIANNING SUN, MD, XIN XIA, MD, LIN XU, MD, AND XUN XU, MD
● PURPOSE:
To investigate whether constant exotropia patients with a previous history of intermittent exotropia X(T), like X(T) patients, can achieve postoperative bifixation, and whether they have a better postoperative sensory outcome than those without previous history of X(T). ● DESIGN: Prospective comparative clinical study. ● METHODS: Sixty-three consecutive patients with intermittent or constant exotropia were divided into three groups: X(T) (group 1), constant exotropia with a previous history of X(T) (group 2), and constant exotropia without previous history of X(T) (group 3). The surgical outcomes were assessed and compared in motor and sensory terms separately between the three groups. Successful motor alignment was defined as within 8 prism diopters (PD) (exo or eso). A stereoacuity <60 seconds of arc was considered as bifixation, and a stereoacuity <800 seconds of arc was considered as gross stereopsis. ● RESULTS: The successful motor alignment rates of group 1, group 2, and group 3 were 79%, 71%, and 67%, respectively (group 1 vs group 2, P ⴝ .826; group 1 vs group 3, P ⴝ .551; group 2 vs group 3, P ⴝ 1.000). Twenty-five (74%) patients in group 1 achieved bifixation and none achieved in group 2 or group 3 (group 1 vs group 2, P ⴝ .001; group 1 vs group 3, P ⴝ .001). Meanwhile, 34 patients (100%) in group 1, 11 (79%) in group 2, and 5 (33%) in group 3 achieved gross stereopsis (group 1 vs group 2, P ⴝ .021; group 2 vs group 3, P ⴝ .025; group 1 vs group 3, P ⴝ .001). Compared with patients in the two constant exotropia groups, patients in X(T) group had a significantly better sensory outcome in both bifixation and gross stereopsis. Patients in group 2 had a
Accepted for publication Jun 16, 2006. From the Department of Ophthalmology, the First People’s Hospital affiliated to Shanghai Jiao Tong University, Shanghai, People’s Republic of China (H.W., X.X., L.X., X.X.); and the Department of Ophthalmology, Zhongda Hospital affiliated to Southeast University, Nanjing, People’s Republic of China (J.S.). Inquiries to Xun Xu, MD, Department of Ophthalmology, the First People’s Hospital affiliated to Shanghai Jiao Tong University, 85 Wu-Jin Road, Shanghai 200080, People’s Republic of China; e-mail: drxuxun@ 163.com
822
©
2006 BY
better sensory outcome than those in group 3 in gross stereopsis. ● CONCLUSIONS: Constant exotropia patients with a previous history of X(T) have a better postoperative sensory outcome in gross stereopsis than those without previous history of X(T), but a worse surgical sensory outcome when compared with X(T) patients in both bifixation and gross stereopsis. Constant exotropia patients decompensated from X(T) may have missed the best time for treatment. (Am J Ophthalmol 2006;142:822– 826. © 2006 by Elsevier Inc. All rights reserved.)
I
NTERMITTENT EXOTROPIA (X[T]) AND CONSTANT EXO-
tropia are known as two common types of strabismus.1 X(T) may be progressive both in degree and frequency of deviation, and eventually deteriorate to constant exotropia. Some believe constant exotropia may represent decompensated X(T),2–5 and others think it is an extensive category also including congenital exotropia, neurologic exotropia, paralytic exotropia, and so on.6 In general, the postoperative sensory outcome of constant exotropia is worse than that of X(T). Ball and associates7 reported that some patients with constant exotropia had achieved bifixation postoperatively; similar results were also found in some constant strabismus.8,9 However, only a minority of patients with constant exotropia can have a superior sensory outcome. Although the factors contributing to the better sensory outcome of some constant exotropia are still unknown, some believe there is a continuum in the intermittency of exotropia or an undetected degree of intermittency in these patients, allowing surreptitious preservation of bifixation.2 To the best of our knowledge, there is no published study regarding the factors contributing to the better sensory outcome in some constant exotropia patients. In the present study, we investigated whether constant exotropia patients with a previous history of X(T), like X(T) patients, can achieve bifixation, and whether they have better sensory outcome postoperatively compared with constant exotropia patients without previous history of X(T).
ELSEVIER INC. ALL
RIGHTS RESERVED.
0002-9394/06/$32.00 doi:10.1016/j.ajo.2006.06.045
TABLE 1. Basic Characteristics of the Three Types of Exotropia Types of Exotropia
n
Age at Surgery* (Years)
Preoperative Acuity†
Deviation Before Surgery‡ (Prism Diopter)
Duration of Exotropia§ (Years)
Group 1 Group 2 Group 3
34 14 15
9.1 ⫾ 4.3 14.1 ⫾ 5.0 14.5 ⫾ 7.9
1.00 (20/20) ⫾ 0.19 0.90 (20/22) ⫾ 0.15 0.90 (20/22) ⫾ 0.22
33.6 ⫾ 7.5 43.9 ⫾ 12.7 50.9 ⫾ 13.1
6.1 ⫾ 3.9 10.6 ⫾ 5.6 12.2 ⫾ 7.9
Group 1 ⫽ Intermittent exotropia; Group 2 ⫽ Constant exotropia with a previous history of intermittent exotropia; Group 3 ⫽ Constant exotropia without previous history of intermittent exotropia. Data are given as mean (⫾SD). *Group 1 vs group 2, P ⫽ .0066; group 1 vs group 3, P ⫽ .0025; group 2 vs group 3, P ⫽ .8224; ANOVA (analysis of variance). † Group 1 vs group 2, P ⫽ .2680; group 1 vs group 3, P ⫽ .4230; group 2 vs group 3, P ⫽ .7786; ANOVA. ‡ Group 1 vs group 2, P ⫽ .0026; group 1 vs group 3, P ⫽ .0001; group 2 vs group 3, P ⫽ .0691; ANOVA. § Group 1 vs group 2, P ⫽ .0124; group 1 vs group 3, P ⫽ .0007; group 2 vs group 3, P ⫽ .4453; ANOVA.
METHODS ● PATIENTS:
A prospective study was conducted on consecutive patients who visited our hospital with intermittent or constant exotropia from July 2003 to September 2004. Informed consent was obtained from the patients or their guardians, and the research protocol was reviewed and approved by the Medical Ethical Committee of our institution. Our inclusion criteria were patients of constant or intermittent exotropia. The X(T) patients should have a preoperative deviation manifesting frequently, often on a daily basis. All patients are able to perform examination and stereopsis tests. To obtain accurate measurements in the sensory tests, the lower limit of age for inclusion was set at four years. Exclusion criteria were paralytic exotropia, a history of previous strabismus surgery, co-existent ocular disease, neurologic or systemic impairment, more than 2 lines of difference in best-corrected visual acuity between both eyes as determined by Snellen letters or illustrated E figures, or more than 2 diopters of anisometropia. Patients who had a true convergence insufficiency were also excluded because they respond poorly to surgical therapy, and treatments in these cases are primarily orthoptic and rarely surgical.10,11 The enrolled patients were divided into three groups: group 1, X(T); group 2, constant exotropia with a previous history of X(T); and group 3, constant exotropia without previous history of X(T). Inclusion of patients in group 2 should meet: (1) A history of X(T). Patients with a history of X(T) often reported that their deviation became manifest when they were fatigued, ill, or lacking concentration, or that one eye squinted in bright light. (2) The angle of exodeviation increased with age and has become stable for more than one year by the time of inclusion. Inclusion of patients in group 3 should meet: (1) Congenital exotropia. (2) Patients were found to have a constant deviation with an unknown or unobserved period in their first year of life because of their negligent guardians or coming to the attention of an ophthalmologist later in life.6 The distincVOL. 142, NO. 5
CONSTANT
tion between the two subsets of constant exotropia was based on a complete history record provided by the patients or their guardians. ● EXAMINATION AND DATA COLLECTION: All patients underwent a complete ophthalmologic examination before operation. Data collected included the gender, visual acuity with refractive error corrected, age of surgery, duration of exotropia, and deviation when fixating at a near target (33 cm) and a distant target (6 m) pre- and postoperatively. The maximum angle of deviation was measured by applying the alternate cover and prism test with loose prisms. Binocular functions were investigated and the results were recorded. The preoperative and postoperative sensory statuses were determined in all patients by the Titmus (Titmus Optical Co, Petersburg, Virginia, USA) stereoacuity test.12 A stereoacuity ⱕ60 seconds of arc was defined as bifixation and a stereoacuity ⱕ800 seconds of arc was defined as gross stereopsis. Patients who exhibited no stereopsis were recorded as nil for the purpose of calculation. The length of follow-up was at least one year. ● OPERATION:
All patients in the present study were advised for surgery as soon as the diagnosis was confirmed and reliable measurements were obtained. Patients with significant refractive errors were corrected before determining the amount of surgical intervention.13 Types of surgery consisted of bilateral lateral rectus recessions and recess/resect procedures. The amount of surgery was based on the distance deviation.14 Overcorrection of the horizontal deviation was desirable in the immediate postoperative period.15,16 X(T) patients with consecutive esotropia persisting for six weeks after surgery were prescribed base-out prisms to neutralize the distance deviation. If esotropia at near was present despite the use of prisms, appropriately powered bifocal adds were prescribed to neutralize the near deviation.2 Reoperation was recommended if consecutive esotropia of greater than 10 prism diopter (PD) was still present at six months, even if well compensated by prisms.17
AND INTERMITTENT
EXOTROPIA
823
TABLE 2. Pre- and Postoperative Titmus Stereoacuity Test Results of the Three Types of Exotropia
TABLE 3. Surgical Outcomes of the Three Types of Exotropia
Titmus Stereoacuity Test Results Types of Exotropia
Group 1 (n ⫽ 34) Group 2 (n ⫽ 14) Group 3 (n ⫽ 15)
Preoperative 1 year postoperative Preoperative 1 year postoperative Preoperative 1 year postoperative
Bifixation
Gross Stereopsis
12 25
33 34
1 0
0 0
3 11
11 3
0 0
1 5
14 10
Surgical Outcome
Nil
Group 3 (n ⫽ 15)
*Group 1 vs Group 2, P ⫽ .826; Group 1 vs Group 3, P ⫽ .551; Continuity Adj. Chi-square. Group 2 vs Group 3, P ⫽ 1.000; Fisher exact test. † Group 1 vs Group 2, P ⫽ .001; Group 1 vs Group 3, P ⫽ .001; Chi-square test. ‡ Group 1 vs Group 2, P ⫽ .021; Group 2 vs Group 3, P ⫽ .025; Fisher exact test. Group 1 vs Group 3, P ⫽ .001; Continuity Adj. Chi-square. Group 1 ⫽ Intermittent exotropia; Group 2 ⫽ Constant exotropia with a previous history of intermittent exotropia; Group 3 ⫽ Constant exotropia without previous history of intermittent exotropia.
● SURGICAL OUTCOME ASSESSMENT:
The surgical outcomes were evaluated in motor and sensory terms separately. Successful motor alignment was defined as a horizontal deviation of 0 to 8 PD (exo or eso) with fixation on an accommodative target at 6 m (distance fixation) and at 0.33 m (near fixation) during the most recent follow-up examination, at least one year postoperatively. Successful sensory alignment was defined as achievement of bifixation. A stereoacuity ⱕ60 seconds of arc was considered as bifixation and a stereoacuity ⱕ800 seconds of arc was considered as gross stereopsis.
⫽ .0001; ANOVA), and a shorter duration of exotropia (group 1 vs group 2, P ⫽ .0124; group 1 vs group 3, P ⫽ .0007; ANOVA) compared with patients in either of the two constant exotropia groups. However, patients in group 2 and group 3 showed no significant difference in age at surgery (P ⫽ .8224, ANOVA), in preoperative deviation (P ⫽ .0691, ANOVA), and in duration of exotropia (P ⫽ .4453, ANOVA). The preoperative acuity was not significantly different between the three groups (group 1 vs group 2, P ⫽ .2680; group 1 vs group 3, P ⫽ .4230; group 2 vs group 3, P ⫽ .7786; ANOVA).
● STATISTICAL ANALYSIS:
Statistical comparison consisted of the t test, analysis of variance (ANOVA), 2 test, and Fisher exact test, where appropriate. Probability values ⬍.05 were considered statistically significant. All analyses were done with SAS 6.12 (Statistics Analytical Software; SAS Institute, Cary, North Carolina, USA).
● SURGICAL RESULTS:
Of all the patients in the three groups, 47(75%) achieved successful motor alignment: 27 (79%) in group 1, 10 (71%) in group 2, and 10 (67%) in group 3, with no significant difference found between the three groups (group 1 vs group 2, P ⫽ .826; group 1 vs group 3, P ⫽ .551; Continuity Adj. 2 test; group 2 vs group 3, P ⫽ 1.000, Fisher exact test). Of all the patients, 25 (40%) achieved bifixation (all of them achieved successful motor alignment), 50 (79%) achieved gross stereopsis, and 13 (21%) exhibited nil one year after surgery. Table 2 shows the preand postoperative Titmus stereoacuity test results of the three groups. One year after surgery, 25 patients (74%) in group 1 achieved bifixation (ⱕ60”), while no patient in group 2 or group 3 achieved bifixation (group 1 vs group 2, P ⫽ .001; group 1 vs group 3, P ⫽ .001, 2 test); however, 34 patients (100%) in group 1, 11(79%) in group 2, and five (33%) in group 3 achieved gross stereopsis postoperatively (group 1 vs group 2, P ⫽ .021;
RESULTS ● SUBJECT BASIC CHARACTERISTICS: A total of 63 patients were enrolled in this study, including 33 males and 30 females, with a mean age of 11.5 ⫾ 6.0 years (range, 4 to 28 years). Group 1 had 34 patients (22 male, 12 female), group 2 had 14 (five male, nine female), and group 3 had 15 (six male, nine female). Twelve patients in group 3 had congenital exotropia, and three had a constant deviation with an unknown or unobserved period in their first year of life. As shown in Table 1, patients in group 1 had a smaller age at surgery (group 1 vs group 2, P ⫽ .0066; group 1 vs group 3, P ⫽ .0025; ANOVA), a less preoperative deviation (group 1 vs group 2, P ⫽ .0026; group 1 vs group 3, P
AMERICAN JOURNAL
Group 2 (n ⫽ 14)
Successful motor alignment* 27 (79%) 10 (71%) 10 (67%) (0 to 8 PD exo or eso) 25 (74%) 0 0 Bifixation† (stereopsis ⱕ 60”) 34 (100%) 11 (79%) 5 (33.3%) Gross stereopsis‡ (60” ⬍ stereopsis ⱕ 800”)
Group 1 ⫽ Intermittent exotropia; Group 2 ⫽ Constant exotropia with a previous history of intermittent exotropia; Group 3 ⫽ Constant exotropia without previous history of intermittent exotropia.
824
Group 1 (n ⫽ 34)
OF
OPHTHALMOLOGY
NOVEMBER 2006
group 2 vs group 3, P ⫽ .025; Fisher exact test. group 1 vs group 3, P ⫽ .001, Continuity Adj. 2 test). X(T) group had a significantly better sensory outcome than either of the two constant exotropia groups in achieving both bifixation and gross stereopsis. Constant exotropia patients with a previous history of X(T) had a better sensory outcome than those without previous history of X(T) in achieving gross stereopsis (Table 3).
DISCUSSION BALL AND ASSOCIATES7 REPORTED THAT FIVE PATIENTS
with long-standing large-angle constant exotropia unexpectedly achieved stereoacuity following strabismus surgery. They speculated that all the five patients were constant exotropia with a previous history of X(T). They also thought that, if excellent postoperative motor alignment is achieved in constant exotropia patients with good bilateral visual acuity, some of these patients may even achieve bifixation. However, their study was not a comparative one. Abroms and associates2 found nine patients achieved bifixation postoperatively among 31 patients with constant exotropia. Those who achieved bifixation had shorter strabismus durations, but statistical significance was not reached. Here we conducted a prospective and comparative study and found that, although no patient in group 2 and group 3 achieved bifixation even when surgically realigned, the constant exotropia patients with a previous history of X(T) achieved a better postoperative sensory outcome in gross stereopsis compared with those without previous history of X(T). Meanwhile, between group 2 and group 3, there was no significant difference in the preoperative acuity, successful motor alignment, age at surgery, preoperative deviation, and duration of exotropia. Different from the results of the above-mentioned studies, no constant exotropia patients in this study achieved bifixation one year after surgery, even in patients with a previous history of X(T). It might be suggested that patients with constant exotropia deteriorated from X(T) have missed the best time for treatment. Generally, the postoperative bifixation rate is low for patients of constant exotropia. Other studies have reported similar results in infantile exotropia and chronic exotropia.18 –20 The reason why some constant exotropia patients achieved postoperative bifixation in previous studies2,7 is multiple. It may be a joint action of several factors, including a previous intermittence history. Further studies regarding other factors, such as history of amblyopia, are needed. Worries about the early strabismus surgery for patients with intermittent and constant exotropia lasted for many years. From the early concern that persistent overcorrection may result in amblyopia and a loss of stereopsis in visually immature patients21,22 to the recent study that a delay in surgery may result in improved predictability, VOL. 142, NO. 5
CONSTANT
long-term stability, a lower reoperation rate, and a better recovery of stereoacuity.3 The present study showed that timely operation, while the deviation is still intermittent, achieved better sensory outcome than an operation performed after the deviation had deteriorated to constant. Therefore, it is advisable to have timely surgical correction for X(T) before it has a chance to develop into constant exotropia. Criteria vary regarding the successful alignment for patients with intermittent and constant exotropia. Some studies showed that the successful rate of surgery for X(T) was not high.11,23–25 In our study, the successful surgical rate in group 1 was 74% in sensory terms and rose to 79% in motor terms, similar to the results of other studies reporting that patients with intermittent deviations have better surgical outcomes.26 –28 No constant exotropia patient achieved bifixation in this study even when surgically realigned. However, the successful motor alignment rates of group 2 and group 3 were 71% and 67%, respectively, similar to the result of a previous study in which most patients had constant exotropia deteriorated from intermittent exotropia.29 In general, constant exotropia may be divided into two types: constant exotropia with a previous history of X(T) and that without previous history of X(T). Since exotropia patients associated with abnormalities of the central nervous system, sensory exotropia, and paralytic exotropia were excluded in this study, most of the patients in group 3 were congenital exotropia (12 of 15 patients); the other three patients had an unknown or unobserved period in their first year of life because of their negligent guardians or coming to the attention of an ophthalmologist later in life. The exact causes of the three patients were unknown, most probably congenital exotropia, or decompensated X(T). Hunter and associates18 reported one patient, initially with X(T) deteriorating to constant exotropia in the first year of life. Although such incidence is rare, it may lead to bias to this study. Other limitations of this study include: (1) We evaluated the sensory outcome one year after surgery; however, it is possible that some constant exotropia patients tend to achieve bifixation with time. (2) Because of the small sample size of constant exotropia patients, some statistical analysis could not be performed, warranting more long-term follow-up studies on a larger number of patients. In conclusion, constant exotropia patients with a previous history of X(T) have a better surgical sensory outcome in gross stereopsis than those without previous history of X(T), but a worse surgical sensory outcome in both bifixation and gross stereopsis when compared with patients with X(T). Constant exotropia deteriorated from X(T) may have missed their best time for treatment.
AND INTERMITTENT
EXOTROPIA
825
15. Raab EL, Parks MM. Recession of the lateral recti: early and late postoperative alignments. Arch Ophthalmol 1969;82: 203–208. 16. Rutstein RP, Marsh-Tootle W, Scheiman MM, Eskridge JB. Changes in retinal correspondence after changes in ocular alignment. Optom Vis Sci 1991;68:325–330. 17. Parks MM, Mitchell PR. Concomitant exodeviations. In: Tasman W, Jaeger EA, editors. Duane’s clinical ophthalmology. Volume 1. Philadelphia, Pennsylvania: LippincottRaven, 1995:1–13. 18. Hunter DG, Kelly JB, Buffenn AN, Ellis FJ. Long-term outcome of uncomplicated infantile exotropia. J AAPOS 2001;5:352–356. 19. Biglan AW, Davis JS, Cheng KP, Pettapiece MC. Infantile exotropia. J Pediatr Ophthalmol Strabismus 1996;33:79 – 84. 20. Fujikado T, Matsusaka Y. Binocularity after treatment for constant exotropia. Nippon Ganka Gakkai Zasshi 1994;98: 400 – 403. 21. Jampolsky A. Management of exodeviations. In: Haik G, editor. Strabismus Symposium of the New Orleans Academy of Ophthalmology. St Louis, Missouri: C.V. Mosby, 1962: 140 –143. 22. Jampolsky A. Treatment of exodeviations. In: Crawford JS, Flynn JT, Haik G, Helveston EM, Hoyt CS, Jampolsky A, Parks MM, Scott WE, editors. Pediatric ophthalmology and strabismus: transactions of the New Orleans Academy of Ophthalmology. New York: Raven Press, 1986:201–304. 23. Richard JM, Parks MM. Intermittent exotropia: surgical results in different age groups. Ophthalmology 1983;90: 1172–1177. 24. O’Neal TD, Rosenbaum AL, Stathacopoulos RA. Distance stereo acuity improvement in intermittent exotropic patients following strabismus surgery. J Pediatr Ophthalmol Strabismus 1995;32:353–357. 25. Scott WE, Keech R, Mash JA. The postoperative results and stability of exodeviations. Arch Ophthalmol 1981;99:1814 – 1818. 26. Ing MR, Nishimura J, Okino L. Outcome study of bilateral lateral rectus recession for intermittent exotropia in children. Trans Am Ophthalmol Soc 1997;95:433– 452. 27. Stoller SH, Simon JW, Lininger LL. Bilateral lateral rectus recession for exotropia: a survival analysis. J Pediatr Ophthalmol Strabismus 1994;31:89 –92. 28. Paik HJ, Yim HB. Clinical effect of early surgery in infantile exotropia. Korean J Ophthalmol 2002;16:97–102. 29. Livir-Rallatos G, Gunton KB, Calhoun JH. Surgical results in large-angle exotropia. J AAPOS 2002;6:77– 80.
REFERENCES 1. Yu CB, Fan DS, Wong VW, et al. Changing patterns of strabismus: a decade of experience in Hong Kong. Br J Ophthalmol 2002;86:854 – 856. 2. Abroms AD, Mohney BG, Rush DP, et al. Timely surgery in intermittent and constant exotropia for superior sensory outcome. Am J Ophthalmol 2001;131:111–116. 3. von Noorden GK. Binocular vision and ocular motility: theory and management of strabismus, 4th ed. St Louis, Missouri: C.V. Mosby, 1990:330-339. 4. Hiles DA, Davies GT, Costenbader FD. Long-term observations on unoperated intermittent exotropia. Arch Ophthalmol 1968;80:436 – 442. 5. Romano PE, Romano JA, Puklin JE. Monofixational intermittent exotropia. Arch Ophthalmol 1979;97:1543–1544. 6. Mohney BG. Huffaker RK. Common forms of childhood exotropia. Ophthalmology 2003;110:2093–2096. 7. Ball A, Drummond GT, Pearce WG. Unexpected stereoacuity following surgical correction of long-standing horizontal strabismus. Can J Ophthalmol 1993;28:217–220. 8. Eustis HS, Parks MM. Acquired monofixation syndrome. J Pediatr Ophthalmol Strabismus 1989;26:169 –172. 9. Smoot CN, Simon JW, Nelson LB. Binocularity following surgery for secondary esotropia in childhood. Br J Ophthalmol 1990;74:155–157. 10. Schlossman A, Muchnick RS, Stern KS. The surgical management of intermittent exotropia in adults. Ophthalmology 1983;90:1166 –1171. 11. Yildrim C, Mutlu FM, Chen Y, Altinsoy HI. Assessment of central and peripheral fusion and near and distance stereoacuity in intermittent exotropic patients before and after strabismus surgery. Am J Ophthalmol 1999;128:222–230. 12. Parks MM. Stereoacuity as an indicator of bifixation In: Arruga A, editor. Strabismus symposium: an evaluation of the present status of orthoptics, pleoptics and related diagnostic and treatment regimes. Basel, New York: S. Karger, 1968;258 –260. 13. Gezer A, Sezen F, Nasri N, Gozum N. Factors influencing the outcome of strabismus surgery in patients with exotropia. J AAPOS 2004;8:56 – 60. 14. Ohtsuki H, Hasebe S, Kono R, et al. Prism adaptation response is useful for predicting surgical outcome in selected types of intermittent exotropia. Am J Ophthalmol 2001;131: 117–122.
826
AMERICAN JOURNAL
OF
OPHTHALMOLOGY
NOVEMBER 2006
Biosketch Haixiang Wu, MD, graduated from Nanjing Medical University and has served as an ophthalmology resident at the First People’s Hospital of Nanjing, China. Presently he is doing his PhD degree in Shanghai Jiao Tong University and working as a research fellow in the Department of Ophthalmology, the First People’s Hospital of Shanghai. Meanwhile, he is involved in several important research programs of Shanghai Eye Institute. Strabismus is one of his major research areas.
VOL. 142, NO. 5
CONSTANT
AND INTERMITTENT
EXOTROPIA
826.e1
Biosketch Xun Xu, MD, received his medical degree from Shanghai Medical University (SMU) in 1983. He then worked as an ophthalmologist at the First People’s Hospital of Shanghai until now. His areas of interest includes diabetic retinopathy and proliferative vitreoretinopathy. Currently, Dr Xu is the vice-president of the First People’s Hospital of Shanghai, director of Shanghai Eye Institute and Department of Ophthalmology, the First People’s Hospital Shanghai.
826.e2
AMERICAN JOURNAL
OF
OPHTHALMOLOGY
NOVEMBER 2006
● PURPOSE:
To investigate whether constant exotropia patients with a previous history of intermittent exotropia X(T), like X(T) patients, can achieve postoperative bifixation, and whether they have a better postoperative sensory outcome than those without previous history of X(T). ● DESIGN: Prospective comparative clinical study. ● METHODS: Sixty-three consecutive patients with intermittent or constant exotropia were divided into three groups: X(T) (group 1), constant exotropia with a previous history of X(T) (group 2), and constant exotropia without previous history of X(T) (group 3). The surgical outcomes were assessed and compared in motor and sensory terms separately between the three groups. Successful motor alignment was defined as within 8 prism diopters (PD) (exo or eso). A stereoacuity <60 seconds of arc was considered as bifixation, and a stereoacuity <800 seconds of arc was considered as gross stereopsis. ● RESULTS: The successful motor alignment rates of group 1, group 2, and group 3 were 79%, 71%, and 67%, respectively (group 1 vs group 2, P ⴝ .826; group 1 vs group 3, P ⴝ .551; group 2 vs group 3, P ⴝ 1.000). Twenty-five (74%) patients in group 1 achieved bifixation and none achieved in group 2 or group 3 (group 1 vs group 2, P ⴝ .001; group 1 vs group 3, P ⴝ .001). Meanwhile, 34 patients (100%) in group 1, 11 (79%) in group 2, and 5 (33%) in group 3 achieved gross stereopsis (group 1 vs group 2, P ⴝ .021; group 2 vs group 3, P ⴝ .025; group 1 vs group 3, P ⴝ .001). Compared with patients in the two constant exotropia groups, patients in X(T) group had a significantly better sensory outcome in both bifixation and gross stereopsis. Patients in group 2 had a
Accepted for publication Jun 16, 2006. From the Department of Ophthalmology, the First People’s Hospital affiliated to Shanghai Jiao Tong University, Shanghai, People’s Republic of China (H.W., X.X., L.X., X.X.); and the Department of Ophthalmology, Zhongda Hospital affiliated to Southeast University, Nanjing, People’s Republic of China (J.S.). Inquiries to Xun Xu, MD, Department of Ophthalmology, the First People’s Hospital affiliated to Shanghai Jiao Tong University, 85 Wu-Jin Road, Shanghai 200080, People’s Republic of China; e-mail: drxuxun@ 163.com
822
©
2006 BY
better sensory outcome than those in group 3 in gross stereopsis. ● CONCLUSIONS: Constant exotropia patients with a previous history of X(T) have a better postoperative sensory outcome in gross stereopsis than those without previous history of X(T), but a worse surgical sensory outcome when compared with X(T) patients in both bifixation and gross stereopsis. Constant exotropia patients decompensated from X(T) may have missed the best time for treatment. (Am J Ophthalmol 2006;142:822– 826. © 2006 by Elsevier Inc. All rights reserved.)
I
NTERMITTENT EXOTROPIA (X[T]) AND CONSTANT EXO-
tropia are known as two common types of strabismus.1 X(T) may be progressive both in degree and frequency of deviation, and eventually deteriorate to constant exotropia. Some believe constant exotropia may represent decompensated X(T),2–5 and others think it is an extensive category also including congenital exotropia, neurologic exotropia, paralytic exotropia, and so on.6 In general, the postoperative sensory outcome of constant exotropia is worse than that of X(T). Ball and associates7 reported that some patients with constant exotropia had achieved bifixation postoperatively; similar results were also found in some constant strabismus.8,9 However, only a minority of patients with constant exotropia can have a superior sensory outcome. Although the factors contributing to the better sensory outcome of some constant exotropia are still unknown, some believe there is a continuum in the intermittency of exotropia or an undetected degree of intermittency in these patients, allowing surreptitious preservation of bifixation.2 To the best of our knowledge, there is no published study regarding the factors contributing to the better sensory outcome in some constant exotropia patients. In the present study, we investigated whether constant exotropia patients with a previous history of X(T), like X(T) patients, can achieve bifixation, and whether they have better sensory outcome postoperatively compared with constant exotropia patients without previous history of X(T).
ELSEVIER INC. ALL
RIGHTS RESERVED.
0002-9394/06/$32.00 doi:10.1016/j.ajo.2006.06.045
TABLE 1. Basic Characteristics of the Three Types of Exotropia Types of Exotropia
n
Age at Surgery* (Years)
Preoperative Acuity†
Deviation Before Surgery‡ (Prism Diopter)
Duration of Exotropia§ (Years)
Group 1 Group 2 Group 3
34 14 15
9.1 ⫾ 4.3 14.1 ⫾ 5.0 14.5 ⫾ 7.9
1.00 (20/20) ⫾ 0.19 0.90 (20/22) ⫾ 0.15 0.90 (20/22) ⫾ 0.22
33.6 ⫾ 7.5 43.9 ⫾ 12.7 50.9 ⫾ 13.1
6.1 ⫾ 3.9 10.6 ⫾ 5.6 12.2 ⫾ 7.9
Group 1 ⫽ Intermittent exotropia; Group 2 ⫽ Constant exotropia with a previous history of intermittent exotropia; Group 3 ⫽ Constant exotropia without previous history of intermittent exotropia. Data are given as mean (⫾SD). *Group 1 vs group 2, P ⫽ .0066; group 1 vs group 3, P ⫽ .0025; group 2 vs group 3, P ⫽ .8224; ANOVA (analysis of variance). † Group 1 vs group 2, P ⫽ .2680; group 1 vs group 3, P ⫽ .4230; group 2 vs group 3, P ⫽ .7786; ANOVA. ‡ Group 1 vs group 2, P ⫽ .0026; group 1 vs group 3, P ⫽ .0001; group 2 vs group 3, P ⫽ .0691; ANOVA. § Group 1 vs group 2, P ⫽ .0124; group 1 vs group 3, P ⫽ .0007; group 2 vs group 3, P ⫽ .4453; ANOVA.
METHODS ● PATIENTS:
A prospective study was conducted on consecutive patients who visited our hospital with intermittent or constant exotropia from July 2003 to September 2004. Informed consent was obtained from the patients or their guardians, and the research protocol was reviewed and approved by the Medical Ethical Committee of our institution. Our inclusion criteria were patients of constant or intermittent exotropia. The X(T) patients should have a preoperative deviation manifesting frequently, often on a daily basis. All patients are able to perform examination and stereopsis tests. To obtain accurate measurements in the sensory tests, the lower limit of age for inclusion was set at four years. Exclusion criteria were paralytic exotropia, a history of previous strabismus surgery, co-existent ocular disease, neurologic or systemic impairment, more than 2 lines of difference in best-corrected visual acuity between both eyes as determined by Snellen letters or illustrated E figures, or more than 2 diopters of anisometropia. Patients who had a true convergence insufficiency were also excluded because they respond poorly to surgical therapy, and treatments in these cases are primarily orthoptic and rarely surgical.10,11 The enrolled patients were divided into three groups: group 1, X(T); group 2, constant exotropia with a previous history of X(T); and group 3, constant exotropia without previous history of X(T). Inclusion of patients in group 2 should meet: (1) A history of X(T). Patients with a history of X(T) often reported that their deviation became manifest when they were fatigued, ill, or lacking concentration, or that one eye squinted in bright light. (2) The angle of exodeviation increased with age and has become stable for more than one year by the time of inclusion. Inclusion of patients in group 3 should meet: (1) Congenital exotropia. (2) Patients were found to have a constant deviation with an unknown or unobserved period in their first year of life because of their negligent guardians or coming to the attention of an ophthalmologist later in life.6 The distincVOL. 142, NO. 5
CONSTANT
tion between the two subsets of constant exotropia was based on a complete history record provided by the patients or their guardians. ● EXAMINATION AND DATA COLLECTION: All patients underwent a complete ophthalmologic examination before operation. Data collected included the gender, visual acuity with refractive error corrected, age of surgery, duration of exotropia, and deviation when fixating at a near target (33 cm) and a distant target (6 m) pre- and postoperatively. The maximum angle of deviation was measured by applying the alternate cover and prism test with loose prisms. Binocular functions were investigated and the results were recorded. The preoperative and postoperative sensory statuses were determined in all patients by the Titmus (Titmus Optical Co, Petersburg, Virginia, USA) stereoacuity test.12 A stereoacuity ⱕ60 seconds of arc was defined as bifixation and a stereoacuity ⱕ800 seconds of arc was defined as gross stereopsis. Patients who exhibited no stereopsis were recorded as nil for the purpose of calculation. The length of follow-up was at least one year. ● OPERATION:
All patients in the present study were advised for surgery as soon as the diagnosis was confirmed and reliable measurements were obtained. Patients with significant refractive errors were corrected before determining the amount of surgical intervention.13 Types of surgery consisted of bilateral lateral rectus recessions and recess/resect procedures. The amount of surgery was based on the distance deviation.14 Overcorrection of the horizontal deviation was desirable in the immediate postoperative period.15,16 X(T) patients with consecutive esotropia persisting for six weeks after surgery were prescribed base-out prisms to neutralize the distance deviation. If esotropia at near was present despite the use of prisms, appropriately powered bifocal adds were prescribed to neutralize the near deviation.2 Reoperation was recommended if consecutive esotropia of greater than 10 prism diopter (PD) was still present at six months, even if well compensated by prisms.17
AND INTERMITTENT
EXOTROPIA
823
TABLE 2. Pre- and Postoperative Titmus Stereoacuity Test Results of the Three Types of Exotropia
TABLE 3. Surgical Outcomes of the Three Types of Exotropia
Titmus Stereoacuity Test Results Types of Exotropia
Group 1 (n ⫽ 34) Group 2 (n ⫽ 14) Group 3 (n ⫽ 15)
Preoperative 1 year postoperative Preoperative 1 year postoperative Preoperative 1 year postoperative
Bifixation
Gross Stereopsis
12 25
33 34
1 0
0 0
3 11
11 3
0 0
1 5
14 10
Surgical Outcome
Nil
Group 3 (n ⫽ 15)
*Group 1 vs Group 2, P ⫽ .826; Group 1 vs Group 3, P ⫽ .551; Continuity Adj. Chi-square. Group 2 vs Group 3, P ⫽ 1.000; Fisher exact test. † Group 1 vs Group 2, P ⫽ .001; Group 1 vs Group 3, P ⫽ .001; Chi-square test. ‡ Group 1 vs Group 2, P ⫽ .021; Group 2 vs Group 3, P ⫽ .025; Fisher exact test. Group 1 vs Group 3, P ⫽ .001; Continuity Adj. Chi-square. Group 1 ⫽ Intermittent exotropia; Group 2 ⫽ Constant exotropia with a previous history of intermittent exotropia; Group 3 ⫽ Constant exotropia without previous history of intermittent exotropia.
● SURGICAL OUTCOME ASSESSMENT:
The surgical outcomes were evaluated in motor and sensory terms separately. Successful motor alignment was defined as a horizontal deviation of 0 to 8 PD (exo or eso) with fixation on an accommodative target at 6 m (distance fixation) and at 0.33 m (near fixation) during the most recent follow-up examination, at least one year postoperatively. Successful sensory alignment was defined as achievement of bifixation. A stereoacuity ⱕ60 seconds of arc was considered as bifixation and a stereoacuity ⱕ800 seconds of arc was considered as gross stereopsis.
⫽ .0001; ANOVA), and a shorter duration of exotropia (group 1 vs group 2, P ⫽ .0124; group 1 vs group 3, P ⫽ .0007; ANOVA) compared with patients in either of the two constant exotropia groups. However, patients in group 2 and group 3 showed no significant difference in age at surgery (P ⫽ .8224, ANOVA), in preoperative deviation (P ⫽ .0691, ANOVA), and in duration of exotropia (P ⫽ .4453, ANOVA). The preoperative acuity was not significantly different between the three groups (group 1 vs group 2, P ⫽ .2680; group 1 vs group 3, P ⫽ .4230; group 2 vs group 3, P ⫽ .7786; ANOVA).
● STATISTICAL ANALYSIS:
Statistical comparison consisted of the t test, analysis of variance (ANOVA), 2 test, and Fisher exact test, where appropriate. Probability values ⬍.05 were considered statistically significant. All analyses were done with SAS 6.12 (Statistics Analytical Software; SAS Institute, Cary, North Carolina, USA).
● SURGICAL RESULTS:
Of all the patients in the three groups, 47(75%) achieved successful motor alignment: 27 (79%) in group 1, 10 (71%) in group 2, and 10 (67%) in group 3, with no significant difference found between the three groups (group 1 vs group 2, P ⫽ .826; group 1 vs group 3, P ⫽ .551; Continuity Adj. 2 test; group 2 vs group 3, P ⫽ 1.000, Fisher exact test). Of all the patients, 25 (40%) achieved bifixation (all of them achieved successful motor alignment), 50 (79%) achieved gross stereopsis, and 13 (21%) exhibited nil one year after surgery. Table 2 shows the preand postoperative Titmus stereoacuity test results of the three groups. One year after surgery, 25 patients (74%) in group 1 achieved bifixation (ⱕ60”), while no patient in group 2 or group 3 achieved bifixation (group 1 vs group 2, P ⫽ .001; group 1 vs group 3, P ⫽ .001, 2 test); however, 34 patients (100%) in group 1, 11(79%) in group 2, and five (33%) in group 3 achieved gross stereopsis postoperatively (group 1 vs group 2, P ⫽ .021;
RESULTS ● SUBJECT BASIC CHARACTERISTICS: A total of 63 patients were enrolled in this study, including 33 males and 30 females, with a mean age of 11.5 ⫾ 6.0 years (range, 4 to 28 years). Group 1 had 34 patients (22 male, 12 female), group 2 had 14 (five male, nine female), and group 3 had 15 (six male, nine female). Twelve patients in group 3 had congenital exotropia, and three had a constant deviation with an unknown or unobserved period in their first year of life. As shown in Table 1, patients in group 1 had a smaller age at surgery (group 1 vs group 2, P ⫽ .0066; group 1 vs group 3, P ⫽ .0025; ANOVA), a less preoperative deviation (group 1 vs group 2, P ⫽ .0026; group 1 vs group 3, P
AMERICAN JOURNAL
Group 2 (n ⫽ 14)
Successful motor alignment* 27 (79%) 10 (71%) 10 (67%) (0 to 8 PD exo or eso) 25 (74%) 0 0 Bifixation† (stereopsis ⱕ 60”) 34 (100%) 11 (79%) 5 (33.3%) Gross stereopsis‡ (60” ⬍ stereopsis ⱕ 800”)
Group 1 ⫽ Intermittent exotropia; Group 2 ⫽ Constant exotropia with a previous history of intermittent exotropia; Group 3 ⫽ Constant exotropia without previous history of intermittent exotropia.
824
Group 1 (n ⫽ 34)
OF
OPHTHALMOLOGY
NOVEMBER 2006
group 2 vs group 3, P ⫽ .025; Fisher exact test. group 1 vs group 3, P ⫽ .001, Continuity Adj. 2 test). X(T) group had a significantly better sensory outcome than either of the two constant exotropia groups in achieving both bifixation and gross stereopsis. Constant exotropia patients with a previous history of X(T) had a better sensory outcome than those without previous history of X(T) in achieving gross stereopsis (Table 3).
DISCUSSION BALL AND ASSOCIATES7 REPORTED THAT FIVE PATIENTS
with long-standing large-angle constant exotropia unexpectedly achieved stereoacuity following strabismus surgery. They speculated that all the five patients were constant exotropia with a previous history of X(T). They also thought that, if excellent postoperative motor alignment is achieved in constant exotropia patients with good bilateral visual acuity, some of these patients may even achieve bifixation. However, their study was not a comparative one. Abroms and associates2 found nine patients achieved bifixation postoperatively among 31 patients with constant exotropia. Those who achieved bifixation had shorter strabismus durations, but statistical significance was not reached. Here we conducted a prospective and comparative study and found that, although no patient in group 2 and group 3 achieved bifixation even when surgically realigned, the constant exotropia patients with a previous history of X(T) achieved a better postoperative sensory outcome in gross stereopsis compared with those without previous history of X(T). Meanwhile, between group 2 and group 3, there was no significant difference in the preoperative acuity, successful motor alignment, age at surgery, preoperative deviation, and duration of exotropia. Different from the results of the above-mentioned studies, no constant exotropia patients in this study achieved bifixation one year after surgery, even in patients with a previous history of X(T). It might be suggested that patients with constant exotropia deteriorated from X(T) have missed the best time for treatment. Generally, the postoperative bifixation rate is low for patients of constant exotropia. Other studies have reported similar results in infantile exotropia and chronic exotropia.18 –20 The reason why some constant exotropia patients achieved postoperative bifixation in previous studies2,7 is multiple. It may be a joint action of several factors, including a previous intermittence history. Further studies regarding other factors, such as history of amblyopia, are needed. Worries about the early strabismus surgery for patients with intermittent and constant exotropia lasted for many years. From the early concern that persistent overcorrection may result in amblyopia and a loss of stereopsis in visually immature patients21,22 to the recent study that a delay in surgery may result in improved predictability, VOL. 142, NO. 5
CONSTANT
long-term stability, a lower reoperation rate, and a better recovery of stereoacuity.3 The present study showed that timely operation, while the deviation is still intermittent, achieved better sensory outcome than an operation performed after the deviation had deteriorated to constant. Therefore, it is advisable to have timely surgical correction for X(T) before it has a chance to develop into constant exotropia. Criteria vary regarding the successful alignment for patients with intermittent and constant exotropia. Some studies showed that the successful rate of surgery for X(T) was not high.11,23–25 In our study, the successful surgical rate in group 1 was 74% in sensory terms and rose to 79% in motor terms, similar to the results of other studies reporting that patients with intermittent deviations have better surgical outcomes.26 –28 No constant exotropia patient achieved bifixation in this study even when surgically realigned. However, the successful motor alignment rates of group 2 and group 3 were 71% and 67%, respectively, similar to the result of a previous study in which most patients had constant exotropia deteriorated from intermittent exotropia.29 In general, constant exotropia may be divided into two types: constant exotropia with a previous history of X(T) and that without previous history of X(T). Since exotropia patients associated with abnormalities of the central nervous system, sensory exotropia, and paralytic exotropia were excluded in this study, most of the patients in group 3 were congenital exotropia (12 of 15 patients); the other three patients had an unknown or unobserved period in their first year of life because of their negligent guardians or coming to the attention of an ophthalmologist later in life. The exact causes of the three patients were unknown, most probably congenital exotropia, or decompensated X(T). Hunter and associates18 reported one patient, initially with X(T) deteriorating to constant exotropia in the first year of life. Although such incidence is rare, it may lead to bias to this study. Other limitations of this study include: (1) We evaluated the sensory outcome one year after surgery; however, it is possible that some constant exotropia patients tend to achieve bifixation with time. (2) Because of the small sample size of constant exotropia patients, some statistical analysis could not be performed, warranting more long-term follow-up studies on a larger number of patients. In conclusion, constant exotropia patients with a previous history of X(T) have a better surgical sensory outcome in gross stereopsis than those without previous history of X(T), but a worse surgical sensory outcome in both bifixation and gross stereopsis when compared with patients with X(T). Constant exotropia deteriorated from X(T) may have missed their best time for treatment.
AND INTERMITTENT
EXOTROPIA
825
15. Raab EL, Parks MM. Recession of the lateral recti: early and late postoperative alignments. Arch Ophthalmol 1969;82: 203–208. 16. Rutstein RP, Marsh-Tootle W, Scheiman MM, Eskridge JB. Changes in retinal correspondence after changes in ocular alignment. Optom Vis Sci 1991;68:325–330. 17. Parks MM, Mitchell PR. Concomitant exodeviations. In: Tasman W, Jaeger EA, editors. Duane’s clinical ophthalmology. Volume 1. Philadelphia, Pennsylvania: LippincottRaven, 1995:1–13. 18. Hunter DG, Kelly JB, Buffenn AN, Ellis FJ. Long-term outcome of uncomplicated infantile exotropia. J AAPOS 2001;5:352–356. 19. Biglan AW, Davis JS, Cheng KP, Pettapiece MC. Infantile exotropia. J Pediatr Ophthalmol Strabismus 1996;33:79 – 84. 20. Fujikado T, Matsusaka Y. Binocularity after treatment for constant exotropia. Nippon Ganka Gakkai Zasshi 1994;98: 400 – 403. 21. Jampolsky A. Management of exodeviations. In: Haik G, editor. Strabismus Symposium of the New Orleans Academy of Ophthalmology. St Louis, Missouri: C.V. Mosby, 1962: 140 –143. 22. Jampolsky A. Treatment of exodeviations. In: Crawford JS, Flynn JT, Haik G, Helveston EM, Hoyt CS, Jampolsky A, Parks MM, Scott WE, editors. Pediatric ophthalmology and strabismus: transactions of the New Orleans Academy of Ophthalmology. New York: Raven Press, 1986:201–304. 23. Richard JM, Parks MM. Intermittent exotropia: surgical results in different age groups. Ophthalmology 1983;90: 1172–1177. 24. O’Neal TD, Rosenbaum AL, Stathacopoulos RA. Distance stereo acuity improvement in intermittent exotropic patients following strabismus surgery. J Pediatr Ophthalmol Strabismus 1995;32:353–357. 25. Scott WE, Keech R, Mash JA. The postoperative results and stability of exodeviations. Arch Ophthalmol 1981;99:1814 – 1818. 26. Ing MR, Nishimura J, Okino L. Outcome study of bilateral lateral rectus recession for intermittent exotropia in children. Trans Am Ophthalmol Soc 1997;95:433– 452. 27. Stoller SH, Simon JW, Lininger LL. Bilateral lateral rectus recession for exotropia: a survival analysis. J Pediatr Ophthalmol Strabismus 1994;31:89 –92. 28. Paik HJ, Yim HB. Clinical effect of early surgery in infantile exotropia. Korean J Ophthalmol 2002;16:97–102. 29. Livir-Rallatos G, Gunton KB, Calhoun JH. Surgical results in large-angle exotropia. J AAPOS 2002;6:77– 80.
REFERENCES 1. Yu CB, Fan DS, Wong VW, et al. Changing patterns of strabismus: a decade of experience in Hong Kong. Br J Ophthalmol 2002;86:854 – 856. 2. Abroms AD, Mohney BG, Rush DP, et al. Timely surgery in intermittent and constant exotropia for superior sensory outcome. Am J Ophthalmol 2001;131:111–116. 3. von Noorden GK. Binocular vision and ocular motility: theory and management of strabismus, 4th ed. St Louis, Missouri: C.V. Mosby, 1990:330-339. 4. Hiles DA, Davies GT, Costenbader FD. Long-term observations on unoperated intermittent exotropia. Arch Ophthalmol 1968;80:436 – 442. 5. Romano PE, Romano JA, Puklin JE. Monofixational intermittent exotropia. Arch Ophthalmol 1979;97:1543–1544. 6. Mohney BG. Huffaker RK. Common forms of childhood exotropia. Ophthalmology 2003;110:2093–2096. 7. Ball A, Drummond GT, Pearce WG. Unexpected stereoacuity following surgical correction of long-standing horizontal strabismus. Can J Ophthalmol 1993;28:217–220. 8. Eustis HS, Parks MM. Acquired monofixation syndrome. J Pediatr Ophthalmol Strabismus 1989;26:169 –172. 9. Smoot CN, Simon JW, Nelson LB. Binocularity following surgery for secondary esotropia in childhood. Br J Ophthalmol 1990;74:155–157. 10. Schlossman A, Muchnick RS, Stern KS. The surgical management of intermittent exotropia in adults. Ophthalmology 1983;90:1166 –1171. 11. Yildrim C, Mutlu FM, Chen Y, Altinsoy HI. Assessment of central and peripheral fusion and near and distance stereoacuity in intermittent exotropic patients before and after strabismus surgery. Am J Ophthalmol 1999;128:222–230. 12. Parks MM. Stereoacuity as an indicator of bifixation In: Arruga A, editor. Strabismus symposium: an evaluation of the present status of orthoptics, pleoptics and related diagnostic and treatment regimes. Basel, New York: S. Karger, 1968;258 –260. 13. Gezer A, Sezen F, Nasri N, Gozum N. Factors influencing the outcome of strabismus surgery in patients with exotropia. J AAPOS 2004;8:56 – 60. 14. Ohtsuki H, Hasebe S, Kono R, et al. Prism adaptation response is useful for predicting surgical outcome in selected types of intermittent exotropia. Am J Ophthalmol 2001;131: 117–122.
826
AMERICAN JOURNAL
OF
OPHTHALMOLOGY
NOVEMBER 2006
Biosketch Haixiang Wu, MD, graduated from Nanjing Medical University and has served as an ophthalmology resident at the First People’s Hospital of Nanjing, China. Presently he is doing his PhD degree in Shanghai Jiao Tong University and working as a research fellow in the Department of Ophthalmology, the First People’s Hospital of Shanghai. Meanwhile, he is involved in several important research programs of Shanghai Eye Institute. Strabismus is one of his major research areas.
VOL. 142, NO. 5
CONSTANT
AND INTERMITTENT
EXOTROPIA
826.e1
Biosketch Xun Xu, MD, received his medical degree from Shanghai Medical University (SMU) in 1983. He then worked as an ophthalmologist at the First People’s Hospital of Shanghai until now. His areas of interest includes diabetic retinopathy and proliferative vitreoretinopathy. Currently, Dr Xu is the vice-president of the First People’s Hospital of Shanghai, director of Shanghai Eye Institute and Department of Ophthalmology, the First People’s Hospital Shanghai.
826.e2
AMERICAN JOURNAL
OF
OPHTHALMOLOGY
NOVEMBER 2006