Purpose
To investigate refractive changes after strabismus correction by combined recession of the Medial Rectus (MR) and Inferior Oblique (IO) muscles.
Methods
We reviewed cases of combined MR and IO recession. Individuals with both preoperative refraction measurement and one month postoperative measurements were included. Double-angle mathematical methods for subtraction of refraction were used in order to calculate the surgical induced refractive change. Paired-sample Wilcoxon signed rank test and one-sample binomial tests were used to identify significant postoperative refractive changes. The prevalence of clinically significant changes was also evaluated.
Results
Fifty-five eyes from 28 subjects met the criteria and were included in the final analysis. A substantial rate (>50%) of clinically significant refractive changes resulting in a myopic shift and a positive increase in cylinder power towards with-the-rule direction were observed after combined recession of MR and IO. The rate of significant changes in terms of SE was lower. There was no correlation between the recession extent and amount of refractive change and no significant differences were observed between types of IO weakening procedure.
Conclusion
Refractive changes are a significant side effect of combined recession of MR and IO, and patients should be informed regarding the possibility of such complication prior to the procedure and close postoperative observation is warranted to prevent amblyopia.
A total of 55 eyes from 28 subjects, met the above criteria and were included in the final analysis, of which 31 in the IOR group and 24 in the IOM group. The mean age of the 13 males and 15 females was 3.28 ± 2.11 and 5.93 ± 5.85 years respectively. Table 1 summarizes the baseline characteristics of the study group. No significant differences between the two surgical groups were found in terms of age or preoperative spherocylinder.
Procedure type |
|
Eye no. (subjects) |
Age (years) |
Extent of MR recess (mm) |
Extent of IO recess |
Preoperative Refractive measurements |
|||
(mm) |
Sphere |
Cylinder |
Axis |
SE |
|||||
MR recession |
Mean |
31 |
5.61 |
4.69 |
13.16 |
1.49 |
0.94 |
85.48 |
1.96 |
+ |
SD |
-16 |
5.73 |
1.17 |
1.97 |
3.66 |
0.87 |
60.82 |
3.68 |
IO recession |
Range |
1-22 |
3.0-6.5 |
8.0-15.0 |
-11.5-5.5 |
0.0-3.5 |
0-180 |
-11.3-5.5 |
|
MR recession |
Mean |
24 |
3.58 |
5.01 |
- |
1.7 |
0.92 |
73.54 |
2.16 |
+ |
SD |
-12 |
2.62 |
1.25 |
- |
1.57 |
0.82 |
48.47 |
1.58 |
IO myectomy |
Range |
1-9 |
3.0-7.0 |
- |
-1.8-5.0 |
0.0-3.3 |
0-180 |
-0.8-5.6 |
|
Total |
Mean |
55 |
4.73 |
4.86 |
13.16 |
1.58 |
0.93 |
80.27 |
2.05 |
SD |
-28 |
4.71 |
1.21 |
1.97 |
2.92 |
0.84 |
55.6 |
2.93 |
|
Range |
|
1-22 |
3.0-7.0 |
8.0-15.0 |
-11.5-5.5 |
0.0-3.5 |
0-180 |
-11.3-5.6 |
A summary of preoperative and 1 month postoperative cycloplegic refraction is depicted in table 2. All power parameters (e.g. sphere, cylinder and SE) changed significantly between two measurements (P < 0.05). Statistical significance maintained after stratification according to IO weakening procedure.
Procedure type |
Parameter (diopter) |
Preoperative |
1M Postoperative |
P valuea |
MR recession + IO recession (N=31) |
Sphere |
1.49 ± 3.66 |
1.25 ± 3.61 |
0.011 |
Cylinder |
0.94 ± 0.87 |
1.36 ± 1.18 |
0.007 |
|
SE |
1.96 ± 3.68 |
1.93 ± 3.67 |
0.465 |
|
MR recession + IO myectomy (N=24) |
Sphere |
1.70 ± 1.57 |
1.25 ± 2.02 |
0.001 |
Cylinder |
0.92 ± 0.82 |
1.33 ± 0.84 |
0.001 |
|
SE |
2.16 ± 1.58 |
1.92 ± 1.97 |
0.020 |
|
Total (N=55) |
Sphere |
1.58 ± 2.92 |
1.25 ± 3.00 |
<0.0001 |
Cylinder |
0.93 ± 0.84 |
1.35 ± 1.03 |
<0.0001 |
|
SE |
2.05 ± 2.93 |
1.92 ± 3.03 |
0.024 |
Since the outcome of astigmatic correction depends on the axis as well as the magnitude of the toric change, vector analysis was used to examine these changes. After calculating the SIRC for each eye, the method described by Holladay and colleagues [17] for evaluating and reporting astigmatism for aggregate data was applied. Table 3 summarizes the SIRC according to surgical approach. Overall the magnitude of surgically induced cylinder was found to be significantly different from zero (+0.53 ± 0.67, p < 0.0001) as well as the induced SE (-0.13 ± 0.40, p = 0.028) (Table 3). Statistical significance was maintained in both surgical approaches with the exception for the surgically induced SE which was non-significant in the IO recession group. Figure 1 illustrates the surgically induced cylinder power using a double-angle plot.
Figure 1: Double angle polar plot of astigmatism data using the value of the cylinder for the magnitude and the axis of the astigmatism for the angle.
Parameter (Diopter power), Mean ± SD |
Sphere |
Cylinderb |
Axis (deg.) b |
SE |
P valuec |
P valued |
IO weakening procedure |
||||||
Recession (N = 31) |
-0.45± 0.39 |
0.56 ± 0.56 |
91 |
-0.04 ± 0.26 |
<0.0001 |
0.403 |
Myectomy (N = 24) |
-0.75 ± 0.83 |
0.49 ± 0.76 |
97 |
-0.24 ± 0.51 |
0.0044 |
0.034 |
Total (N = 55) |
-0.61 ± 0.53 |
0.53 ± 0.67 |
94 |
-0.13 ± 0.40 |
<0.0001 |
0.028 |
In a subset of 10 cases a third cycloplegic refraction measurement was available from a subsequent follow-up visit (mean 323 ± 121 days after the surgery), which did not differ significantly from the 1-month postoperative measurement.
We observed a substantial proportion of cases with clinically significant refractive changes after surgery. Figure 2 depicts the proportion of cases where the refractive change was of clinical significance in each parameter. Using one sample binomial test we found all proportions to be significantly different from an acceptable 10% rate for changes equal or greater than 0.5D as well as for changes equal or greater than 0.75D (P < 0.0001). Statistical significance was maintained in all sub-groups after stratification according to surgical technique.
Figure 2: Proportion of cases with clinically significant surgically induced changes in refraction in the IO recession (a) and the IO myectomy (b) groups
No significant association was found between the extent of MR or IO recession and the changes in refractive measurements.
Citation: Daphna M-Z, Tomer Z-B, Ofira Z, Sharon BM, Chaim S, et al. (2019) Refractive Changes Induced by Recession of the Medial Rectus and the Inferior Oblique Muscles. J Ophthalmic Clin Res 6: 053.
Copyright: © 2019 Mezad-Koursh Daphna, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.