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Post-operative
strabismus control and motor alignment for basic intermittent exotropia
Fiona
Chew Lee Min, Bhambi
Uellyn Gesite-de Leon, Boon Long Quah
Department
of Ophthalmology, Singapore National Eye Centre, 11, Third
Hospital Avenue 168751, Singapore
Correspondence to: Fiona
Chew Lee Min. Department
of Ophthalmology,
Singapore
National Eye Centre,
11,
Third Hospital Avenue 168751,
Singapore. sabrefmin@gmail.com
Received: 2015-06-01
Accepted: 2015-08-10
Abstract
Aim: To assess
strabismus control and motor ocular alignment for basic exotropia surgery at 5y
follow-up.
Methods: The medical
records of 80 consecutive patients aged less than 17 years of age, who
underwent surgery for basic exotropia by a single surgeon between years 2000 to
2009 and completed a minimum of 5y follow-up post-operatively were reviewed.
Pre- and post-operative characteristics were documented at 1wk, 6mo, 1, 3 and
5y follow-up. Subjects at 5-year follow-up were assigned to the success group
if they had a post-operative angle of deviation within 10 prism diopters of
exotropia or within 5 prism diopters of esotropia for distance on prism cover
test, and had moderate to good strabismus control. The remaining subjects were
assigned to the failure group.
Results:
Post-operative
surgical success at one week was 75%, which decreased to 41% at 5y follow-up.
The success group was noted to have more patching pre-operatively (P=0.003). The duration of patching a day
(P=0.020) and total duration of
patching pre-operatively (P=0.030)
was higher in the success group. Surgical success at 1y (P=0.004) and 3y (P=0.002)
were associated with higher surgical success at 5y follow-up.
Conclusion:
Post-operative
motor alignment and strabismus control for basic exotropia surgery at 1y and
beyond is
associated with higher exotropia surgery success at 5-year follow-up. There is
an association between pre-operative patching and 5-year surgical success of
basic intermittent exotropia surgery.
KEYWORDS: exotropia;
strabismus control;
intermittent exotropia;
strabismus surgery;
patching;
ocular motor alignment
DOI:10.18240/ijo.2016.07.13
Citation: Chew FLM, Gesite-de Leon
BU, Quah BL. Post-operative
strabismus control and motor alignment for basic intermittent exotropia. Int J Ophthalmol 2016;9(7):1011-1015
INTRODUCTION
Intermittent
exotropia is a horizontal misalignment of the eyes of unknown etiology. The
natural history of this condition remains uncertain[1], but
the prevalence of exotropia in children has been reported to range from 0.01% to
3.3%[2-3]. Children with
exotropia are at higher risk of having binocular abnormalities, visual field
suppression scotomas, depth perception irregularities and amblyopia. In
addition to visual dysfunction, patients with noticeable exotropia tend to
suffer from psychosocial issues such as negative self-image, interpersonal
relationship problems and higher distress levels[4].
Surgically
treated exotropia results in definitive changes to the final angle of
deviation, though reported results vary. Generally, most studies define their
success rate in terms of ocular motor alignment of within 10 prism diopters (PD) of
orthotropia[5-6]. Short-term
studies with 6mo follow-up have reported surgical success rates of
approximately 63%-80%[5-7], whereas
studies with 5y and above follow-up have shown a 32.8%-58%[8-9] success rate
with one surgery. Limited information exists regarding the contribution of
strabismus control as a defining factor for exotropia surgery success in
addition to pure ocular motor alignment. This study aims to assess strabismus
control and motor ocular alignment for basic intermittent exotropia surgery at
5y follow-up.
SUBJECTS AND METHODS
This
retrospective case note review study was conducted in Singapore National Eye
Center (SNEC) and KK Women and Children’s hospital (KKH) from February 2013 to
February 2014. Institutional Review Board (IRB)/Ethics Committee approval was
obtained from the Singhealth Centralized Institutional Review Board on 13
February 2013 (reference number: 2013/068/A) and this research adhered to the
tenets of the Declaration of Helsinki. Consecutive children with basic
exotropia of less than 17y of age who underwent strabismus surgery under
general anaesthesia by a single surgeon (Quah BL) from 1st January
2000 to 1st January 2009 were identified from the SNEC and KKH
clinic database. The patients were included as study subjects if they had
completed at least 5y of post-operative follow-up. Intermittent exotropia was
diagnosed if the patients developed a comitant intermittent exodeviation after
one year of age but before 5y of age. Basic exotropia was diagnosed if the
patients with intermittent exotropia had a difference between the distance and
near manifest exodeviation of within 10 PD on alternate prism cover testing[10]. Exodeviation
control for distance was divided into 3 groups, which were good, moderate and
poor control. The amount of control
was defined by the recovery from exodeviation after cover testing. Subjects
with good control had immediate recovery. Subjects with moderate control
recovered with a blink and subjects with poor control remained in exodeviation
post alternate cover testing.
Data collected from the subjects’ case notes
included gender, ethnicity, age of subject at presentation (at
our eye centre), age of subject at time of surgery, exodeviation for distance
pre-operatively and post-operatively, stereopsis pre- and post-operatively,
amblyopia pre- and post-operatively, refractive errors pre- and
post-operatively, patching pre- and post-operatively, control of strabismus
pre- and post-operatively and post-operative motor alignment at 1wk, 6mo, 1, 3
and 5y.
Subjects were
excluded if they had any dissociated vertical deviation, vertical deviation or
A or V pattern or re-operation for residual horizontal strabismus. Further
exclusion criteria were if the subjects had dense intractable amblyopia, had
ocular abnormalities other than refractive error or had previous ocular trauma,
laser or surgery. Subjects with neurological disorders and who were born premature
were also excluded.
All subjects had
visual acuity assessment with age-appropriate devices (Snellen chart,
K-pictures) and stereopsis examination with Frisby. A one-hour patch test was
performed for all subjects before a prism alternate cover test with appropriate
refractive error correction, to determine the angle of exotropia in PD at 6 m and
30 cm.
Examination of the anterior segment of both eyes of the subjects was performed,
followed by a cycloplegic refraction and examination of the posterior segment
of both eyes.
Patients
were listed for surgery if during follow-up, their intermittent exotropia
progressed to constant exotropia, or they had intermittent exotropia with poor
control. Pre-operatively, there was no standardized patching regime and the
duration of patching was not uniform. However, all patients were advised on
part-time patching of one to four hours duration of the preferred eye for
fixation, or alternate eye patch if they alternated fixation. All patients had
bilateral lateral rectus (BLR)
muscle recession according to standard surgical tables[11].
Post-operatively, subjects were offered part-time patching of one to four hours
duration as anti-suppressant
therapy if they had amblyopia or residual exotropia with moderate or poor control.
Post-operatively,
subjects had similar ophthalmological assessments at 1wk, 6mo, 1, 3 and 5y
follow-up. The criteria for successful post-operative motor alignment at
distance was an angle of deviation of less than or equal to 10 PD of exotropia
or less than or equal to 5 PD of esotropia. Subjects were considered
under-corrected if they had postoperative alignment of more than 10 PD of
exotropia and over-corrected if they had a postoperative alignment of more than
5 PD of esotropia. For statistical analysis, esotropia was assigned a plus sign
while exotropia was assigned a minus sign.
The subjects
recruited were assigned to two groups, which were the success group and the
failure group. Subjects were assigned to the success group if they fulfilled
the success criteria for post-operative motor alignment for distance and had
moderate to good strabismus control at 5y follow-up. The remaining subjects
were assigned to the failure group. Stereopsis was not used as a success
criteria, as some subjects were too young to perform the Frisby test reliably.
Statistical
Analysis
Standardized forms were used for
data collection and the collected data was entered into an Excel spreadsheet.
Data analysis was performed using SPSS version 13 (SPSS Statistics: Windows Student
Version 13, Chicago, IL, USA).
Independent samples t-test was for
continuous variables to calculate the differences between the means. Binary
logistic regression was used to calculate multiply adjusted odds ratio,
confidence intervals and the calculated probability value (P value). P value of
<0.05 was taken as statistically significant.
RESULTS
Eighty subjects
fulfilled the study inclusion criteria and completed the five-year follow-up.
Of the 80 subjects recruited, 33 subjects were assigned to the success group
and 47 subjects were assigned to the failure group. Of these 80 subjects, 88%
were of Chinese, 6% were of Malay and 6% were of Indian descent. There were
slightly more male than female subjects (40 males, 40 females).
The subjects’
age at first presentation at our eye center ranged from 1 to 14y of age with a
mean age of 4.45±2.50y.
The subjects’ age at surgery ranged from 2 to 15y of age with a mean of 6.85±2.85y. The
duration from first presentation till surgery ranged from 1-156mo with a mean
of 27.65±25.94mo.
Three quarters of the subjects (60/80) had their surgery within 36mo of first
presentation.
Best corrected
visual acuity pre-operatively ranged from 6/6 to 6/12 and 6/6 to 6/9 in the
right and left eye respectively. At the time of surgery, the mean spherical
equivalent for the subjects was -0.11±1.73 and -0.24±1.94 diopters (D) for
the right and left eye respectively and the majority of the subjects were not
amblyopic (96%, 77/80). Pre-operative stereopsis ranged from 40s of arc to 600s of
arc with a mean of 87.5±86.74 and stereopsis could not be measured in 12
subjects, as they were too young.
Subjects in the
success group had smaller pre-operative angles of deviation for distance in
comparison to subjects in the failure group and the result was significant (P=0.015). There was no statistically
significant difference between the two groups pre-operatively in terms of
ethnicity, gender, presenting age, age at surgery, duration till surgery,
visual acuity, pre-operative spherical equivalent, stereopsis, presence of
amblyopia and pre-operative control of strabismus (Tables 1, 2).
Table
1 Demography of subjects
Parameters |
Success (n=33) |
Failure (n=47) |
Multiply
adjusted odds ratioa |
||
Odds
ratio |
CI |
P |
|||
Race (Chinese/other) |
28:5 |
42:5 |
0.332 |
0.033,
3.306 |
0.347 |
Gender (M/F) |
16:17 |
24:23 |
1.124 |
0.439, 2.882 |
0.807 |
Age at
presentation (a) |
4.53±2.29 |
4.40±2.66 |
0.773 |
0.399, 1.497 |
0.446 |
Age at surgery
(a) |
7.03±2.67 |
6.72±2.99 |
1.357 |
0.728, 2.528 |
0.336 |
Duration till
surgery (mo) |
27.27±21.70 |
27.91±28.78 |
0.976 |
0.922, 1.032 |
0.390 |
CI:
Confidence interval.
aOdds
ratio adjusted for race, gender, age at presentation, age at surgery, duration
till surgery.
Table 2 Pre-operative subject characteristics
Parameters |
Success (n=33) |
Failure (n=47) |
Multiply
adjusted odds ratioa |
||
Odds
ratio |
CI |
P |
|||
VAR
(6/6-6/9:worse) |
26:7 |
36:11 |
0.762 |
0.088, 6.594 |
0.805 |
VAL
(6/6-6/9:worse) |
27:6 |
36:11 |
2.896 |
0.262, 32.052 |
0.386 |
SER
|
0.11±1.18 |
-0.29±2.08 |
1.114 |
0.641, 1.937 |
0.701 |
SEL |
-0.24±1.99 |
-0.28±1.99 |
0.991 |
0.605, 1.621 |
0.970 |
Far deviation (PD) |
29.67±10.54 |
34.94±9.54 |
0.922 |
0.864, 0.984 |
0.015 |
Patching (yes:no) |
26:7 |
21:26 |
7.846 |
2.054, 29.967 |
0.003 |
Stereopsis
(seconds of arc) |
87.83±108.78 |
87.27±69.22 |
1.00 |
0.993, 1.006 |
0.883 |
Control for far (moderate:poor) |
4:29 |
9:38 |
0.369 |
0.067, 2.030 |
0.252 |
VA:
Visual acuity; R:
Right eye; L: Left eye;
SE: Spherical equivalent; PD: prism diopters. aOdds ratio
adjusted for VAR, VAL, SER, SEL,
stereopsis, far deviation, control for far and patching.
More
subjects in the success group (79%) had pre-operative patching in comparison to
45% of the failure group subjects and the result was statistically significant
(multiply adjusted odds ratio, P=0.003).
The success group subjects were also noted to have significantly longer hours
of patching per day, and more months of patching pre-operatively in comparison
to failure group subjects. The type of patching (alternate or unilateral
patching) done pre-operatively was not statistically significant between the
two groups (Table 3).
Table 3 Pre-operative patching in study subjects
Parameters |
Success (n=26) |
Failure (n=21) |
Multiply
adjusted odds ratioa |
||
Odds
ratio |
CI |
P |
|||
Duration of
patching per day (h) |
3.12±0.98 |
2.31±0.85 |
4.639 |
1.403,
15.332 |
0.020 |
Total duration
of patching (mo) |
15.79±7.88 |
8.92±2.47 |
1.353 |
1.002,
1.826 |
0.030 |
Type of
patching (alternate:
one eye) |
24:2 |
18:3 |
0.362 |
0.037,
2.471 |
0.402 |
CI: Confidence
interval. aOdds
ratio adjusted for duration of patching per day, total duration of patching,
type of patching.
At
5-year follow-up, best-corrected visual acuity ranged between 6/6-6/9 for both
eyes, and 4% (3/80) of the subjects were amblyopic. Post-operative stereopsis
at 5y follow-up ranged from 40s of arc to 215s of arc with a mean of
56.44±34.20. There was no statistically significant difference between visual
acuity, amblyopia, stereopsis and mean spherical equivalents between the
success and failure groups at 5-year follow-up. More patients in the failure
group had post-operative patching in comparison to the success group. The
difference however, was not statistically significant between the two groups
(Table 4).
Table
4
Post-operative characteristics of
subjects at 5 years follow-up
Parameters |
Success (n=33) |
Failure (n=47) |
Multiply adjusted odds ratioa |
||
Odds ratio |
CI |
P |
|||
VAR (6/6-6/9:Worse) |
31:2 |
44:3 |
0.457 |
0.045, 4.624 |
0.507 |
VAL (6/6-6/9:Worse) |
31:2 |
45:2 |
0.845 |
0.079, 9.016 |
0.889 |
SER |
-2.60±2.41 |
-1.93±2.58 |
0.869 |
0.653, 1.158 |
0.338 |
SEL |
-2.46±2.71 |
-1.81±2.65 |
1.024 |
0.795, 1.321 |
0.852 |
Amblyopia (yes:
no) |
1:32 |
2:45 |
36.02 |
0.000, 8.467 |
0.716 |
Stereopsis (seconds
of arc) |
59.85±36.58 |
54.04±32.61 |
1.007 |
0.992, 1.021 |
0.353 |
Patchingb (yes:
no) |
3:30 |
13:34 |
0.182 |
0.032, 1.042 |
0.056 |
CI: Confidence
interval; VA:
Visual acuity; SE:
Spherical equivalent; R:
Right eye; L:
Left eye. aOdds
ratio adjusted for VAR, VAL, SER, SEL,
amblyopia, stereopsis, patching. bPatching at any point in time
post-operatively.
Post-operative
strabismus control in the failure group worsened after 6mo. Moderate to good
strabismus control in the 1st and 3rd post-operative year
was associated with higher possibility of surgical success in the 5th
post-operative year
(Table
5).
Table 5 Association
between post-operative strabismus control and 5-year surgical success
Parameters |
Success (5a, n=33) |
Failure (5a, n=47) |
Multiply
adjusted odds ratioa |
||
Odds
ratio |
CI |
P |
|||
Moderate to
good:Poor |
|
|
|
|
|
1wk control |
28:5 |
38:9 |
1.437 |
0.349, 5.906 |
0.615 |
6mo |
24:9 |
46:1 |
0.301 |
0.054, 1.666 |
0.169 |
1a |
28:5 |
22:25 |
4.677 |
1.072, 20.412 |
0.040 |
3a |
27:6 |
19:28 |
3.788 |
1.059, 13.549 |
0.041 |
aOdds ratio adjusted for strabismus
control at 1wk, 6mo, 1 and 3y follow-up.
Post-operative
surgical success was 75%, 51%, 80%, 45% and 41% for 1wk, 6mo, 1, 3
and 5y follow-up respectively. No intra-operative complications were
documented. Surgical success at 1 and 3y post-operatively was predictive of
5-year surgical success with surgical success at 3y being the strongest
predictive factor
(Table
6).
Table
6
Association between time of follow-up
and 5-year surgical success
Parameters |
Success (5a, n=33) |
Failure (5a, n=47) |
Multiply adjusted odds ratioa |
||
Odds ratio |
CI |
P |
|||
Success:Fail |
|
|
|
|
|
1wk |
25:8 |
35:12 |
1.171 |
0.251, 5.474 |
0.841 |
6mo |
23:10 |
18:29 |
0.722 |
0.175, 2.973 |
0.652 |
1a |
30:3 |
24:23 |
10.442 |
2.137, 51.025 |
0.004 |
3a |
27:6 |
9:38 |
22.906 |
5.446, 96.341 |
0.002 |
aOdds ratio adjusted for surgical success
at 1wk, 6mo, 1 and 3y follow-up.
DISCUSSION
Exotropia
in general has been reported to be seven times more common than esotropia, and
have a prevalence of 0.67% in Singaporean Chinese children aged 6 to 72mo[12]. Most studies
on exotropia surgery had a short follow-up of less than 5y and noted a
correlation between early and final post-operative motor alignment[13]. Few studies
however focused on surgical success based on sensory status in addition to
motor alignment[14-15]. This is the
first study from Singapore reporting the results from a single surgeon with the
longest period of follow-up for intermittent exotropia surgery which takes into
account surgical success based on strabismus control in addition to motor
alignment.
The
success rate for intermittent exotropia surgery at one-year follow-up in
previous Singaporean studies has been reported as 56.8%[16] to 65.2%[17]. Our study
success rate at one-year follow-up of 68% was comparable to those studies. We
noted that our study success rate decreased with the length of follow-up, and
our final study success rate at five-year follow-up (41%) was lower than
long-term studies of exotropia from other countries which reported success
rates of 51%[18] to
58.2%[19] at mean
follow-up of period of 3 to 4y. This could be because we used more stringent
criteria for surgical success, where we factored in control of strabismus in
addition to motor alignment. We noted that study subjects in both groups were
more myopic at the end of five-year follow-up. This reflected the increasing
myopic trend in Singaporean children[20] and also echoes
Ekdawi et al’s study[21] which noted a
myopic trend was common in intermittent exotropia patients.
We
also found that surgical success at 1wk and 6mo were not indicative of long-term
surgical success at 5y follow-up, in contrast to the 1 and 3y results. This may
be due to the healing period of ocular tissue and that the eyes needed time to
adapt to the new ocular alignment post-operatively. Surgical success and
strabismus control at 1y and beyond was associated with higher surgical success
rates at 5y follow-up. Interestingly when looking at the success rates, there
seemed to be minor fluctuations where the success rates would not linearly
decrease with time. This may be due to strabismus control, which could be
improved with orthoptic exercises.
Our
study success group had smaller pre-operative angle of deviation for distance
in comparison to the failure group. This finding concurred with Lee et al
[22] who noted that
larger pre-operative angles of deviation for distance was associated with
larger angles of exotropia recurrence post-operatively. Pre-operative control
of strabismus did not significantly affect final surgical outcome as majority
of our subjects had moderate to poor control pre-operatively.
Patching
is commonly used for the treatment of amblyopia, limited data however exists
for the role of patching for exotropia surgery. Cho et al[23] suggested that
patching pre- and post-operatively reduced the recurrence of post-operative
exotropia. Though all of our patients were advised to do pre-operative
patching, not all were compliant as certain children refused to patch and some
parents were not keen on patching therapy.
Our
study found that there was an association between pre-operative patching and
5-year surgical success, where more subjects in the success group (79%)
had patching in comparison to the failure group (45%) (Table 3). We also noted that subjects
in the success group patched one hour longer per day in comparison to subjects
in the failure group (P=0.020). The
total duration of patching pre-operatively in the success group (mean: 15.8mo)
was longer than the failure group (mean: 8.9mo). There was no statistically
significant difference between post-operative patching for both groups at
5-year follow-up after adjusting for multiple variables. Also, more subjects
(9%) in the failure group required patching in comparison to the success group
(17.5%) as subjects in the failure group. We were unable to comment on the role
of post-operative patching in this study as post-operative patching was not
equally distributed as study subjects were only offered patching therapy
post-operatively if they had poor squint control or amblyopia. We suggest a
randomized control trial in the future to look at the effects of pre- and
post-operative patching for basic intermittent exotropia surgery.
Our
study limitations were that it was a retrospective study with a small number of
patients. Another limitation was that the visual acuity was not taken using
logMAR. Further limitations are that there are many unknowns regarding the
pre-op patching regime as this was a retrospective study, there was no
standardized patching regime, the amount, duration and compliance of patching
was based on parental report, and the indications and reasons for patching and
reasons for patching were not documented in patient’s charts.
Our
study is unique as it is one of the few studies[23] that noted an
association between preoperative eye patching and the success of intermittent
exotropia surgery. We are also one of the few studies who classified
intermittent exotropia surgical success according to strabismus control in
addition to motor alignment. To our knowledge, this is the first study from
Singapore to present complete 5-year follow-up data for all subjects operated
by a single surgeon to study the relationship of early and late post-operative
success.
ACKNOWLEDGEMENTS
Conflicts
of Interest: Chew FLM, None; Gesite-de Leon BU, None; Quah BL, None.
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