Dose-Effect Relationship of Unilateral Medial Rectus Resection for Recurrent Exotropia

Young Kwon Chung; Se Yup Lee; Young Chun Lee

doi:10.7469/JKOS.2015.56.03.420

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Chung, Lee, and Lee: Dose-Effect Relationship of Unilateral Medial Rectus Resection for Recurrent Exotropia

Original Article

J Korean Ophthalmol Soc 2015;56(3):420-426.

Published online: 7 September 2015

DOI: https://doi.org/10.7469/JKOS.2015.56.03.420

Dose-Effect Relationship of Unilateral Medial Rectus Resection for Recurrent Exotropia

Young Kwon Chung, MD¹, Se Yup Lee, MD, PhD², Young Chun Lee, MD, PhD¹

¹Department of Ophthalmology and Visual Science, The Catholic University of Korea College of Medicine, Seoul, Korea

²Department of Ophthalmology, Keimyung University School of Medicine, Daegu, Korea

￭ Address reprint requests to Young Chun Lee, MD, PhD Department of Ophthalmology, College of Medicine, The Catholic University of Korea, Uijeongbu St. Mary’s Hospital, #271 Cheonbo-ro, Uijeongbu 480-717, Korea Tel: 82-31-820-3022, Fax: 82-31-847-3418 E-mail: yclee@cmcnu.or.kr

Received 13 June 20144 November 2014 Accepted 2 March 2015

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

초록

Purpose:

To investigate the dose-effect relationship of unilateral medial rectus resection for recurrent exotropia after bilateral lateral rectus recession.

Methods:

This study comprised 39 patients who underwent unilateral medial rectus resection for recurrent exotropia under 25 PD and bilateral rectus recession for prior surgery of exotropia. The medial rectus was resected from 5.0 to 7.0 mm according to angle deviation at a distance. The postoperative deviated angle was checked at one week, 3 months and 6 months postoperatively to investigate the amount of corrected deviation per resected muscle.

Results:

The average preoperative deviation was 21.33 ± 2.96 PD. We resected mean 6.26 ± 0.57 mm of the medial rectus muscle. The postoperative deviated angle was 0.82 ± 3.47, 1.87 ± 3.10 and 5.40 ± 4.79 PD at 1 week, 3 months and 6 months after surgery, respectively. The corrected deviated angle per millimeter (mm) was 3.29 ± 0.68, 3.17 ± 0.58 and 2.75 ± 0.89 PD at 1 week, 3 months and 6 months after surgery. There were no significant differences among the changes of postoperative deviation per millimeter according to the amount of medial rectus (MR) resection ( p-value = 0.423, 0.382) The success rate was 89.75%, 92.31% and 87.18% at 1 week, 3 months and 6 months after surgery, respectively. The expected corrected angle according to the amount of resection remained constant and was 3.04-3.22 PD/mm at 3 months after surgery and 2.79-2.82 PD/mm at 6 months after surgery.

Conclusions:

The dose-effect per millimeter was decreased as time passed. There was no statistical difference among the corrected deviation angles per millimeter according to the amount of MR resection. We expect that the calculated dose-effect relationship may be a useful guideline for unilateral medial rectus resection for recurrent exotropia.

Keywords: Dose-effect, Exotropia, Medial rectus resection, Recurrent exotropia, Unilateral medial rectus resection

References

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Figure 1.

Correlation between preoperative distance deviation and medial rectus resection. R² = correlation coefficient; PD = prism diopter.

Figure 2.

Postoperative exodrift after secondary operation as time passed. PD = prism diopter; POD = postoperation day.

Figure 3.

The graph of change of postoperative deviation per a millimeter according to the length of medial rectus muscle resection. PD = prism diopter; MR = medial rectus.

Figure 4.

The graph of expected change in deviation on the basis of unilateral medial rectus resection and the regression equation. R² = correlation coefficient.

Figure 5.

Expected change in deviation on one millimeter in unilateral medial rectus resection (A: 3 months; B: 6 months). PD = prism diopter.

Table 1.

The preoperative exodeviation according to the amount of unilateral medial rectus resection

Amount of MR resection (mm)	Number of patients	Preoperative deviated angle (PD)
5	2	18.0 ± 2.83
5.5	5	20.6 ± 2.61
6	11	19.8 ± 2.86
6.5	12	21.3 ± 2.26
7	9	24.4 ± 1.67

Values are presented as mean ± SD unless otherwise indicated.

MR = medial rectus; PD = prism diopter.

Table 2.

Preoperative patients data

Mean age of onset (years)	3.58 ± 2.24 (1-16)
Number of patients (M/F)	39 (16/23)
Mean age at surgery (years)
Primary operation	6.23 ± 3.69 (3-20)
Reoperation	11.05 ± 4.76 (6-27)
Time to reoperation after primary surgery (years)	4.82 ± 2.93 (1-13)
Preoperative deviation before primary operation (PD)	30.81 ± 7.02 (20-50)
Preoperative deviation before reoperation (PD)	21.33 ± 2.96 (16-25)
Amount of UMR resection (mm)	6.26 ± 0.57 (5.5-7.0)

Values are presented as mean ± SD unless otherwise indicated.

PD = prism diopter; UMR = unilateral medial rectus.

Table 3.

Surgical outcome of unilateral MR resection as the second operation for recurrent exotropia at postoperative 1 week, 3 months, 6 months

	Success rate (%)	Overcorrection (%)	Undercorrection (%)
POD 1 week	35 (89.75)	3 (7.69)	1 (2.56)
POD 3 months	36 (92.31)	0 (0)	3 (7.69)
POD 6 months	34 (87.18)	0 (0)	5 (12.82)

MR = medial rectus; POD = postoperation day.

Table 4.

The amount of resected MR and corrected PD/mm according to deviated angle

Angle deviation	Number	Amount of MR resection	Corrected PD/mm at POD 3 months	Corrected PD/mm at POD 6 months
16-18	7	5.79 ± 0.36	2.73 ± 0.54	2.18 ± 0.82
20	18	6.17 ± 0.51	3.02 ± 0.57	2.66 ± 0.91
25	14	6.63 ± 0.49	3.57 ± 0.38	3.15 ± 0.71
Summary	39	6.26 ± 0.57	3.17 ± 0.58	2.75 ± 0.89

Values are presented as mean ± SD unless otherwise indicated.

MR = medial rectus; PD = prism diopter; POD = postoperation day.

Table 5.

Change of postoperative deviation per a millimeter according to the length of MR res

MR resection (mm)	Change of postoperative deviation per 1 mm
MR resection (mm)	1 week	3 months	6 months
5	3.60 ± 0.57	3.60 ± 0.57	3.00 ± 1.41
5.5	3.60 ± 0.70	3.38 ± 0.40	3.38 ± 0.40
6	3.24 ± 1.26	2.91 ± 1.05	2.52 ± 1.38
6.5	3.14 ± 0.74	2.99 ± 0.65	2.55 ± 0.86
7	3.30 ± 0.94	3.49 ± 0.24	2.89 ± 0.87
Average	3.29 ± 0.68	3.17 ± 0.58	2.75 ± 0.89

Values are presented as mean ± SD.

MR = medial rectus.

Table 6.

Expected change in deviation on the basis of unilateral medial rectus resection

UMR resection (mm)	Change in deviation (PD)(3 months)	Change in deviation per 1 mm (3 months)	Change in deviation (PD)(6 months)	Change in deviation per 1 mm (6 months)
4	11.55	2.888	11.08	2.770
5	15.22	3.043	13.96	2.792
5.5	17.05	3.099	15.40	2.800
6	18.88	3.146	16.84	2.806
6.5	20.71	3.186	18.28	2.812
7	22.54	3.220	19.72	2.817
7.5	24.37	3.250	21.16	2.821
8	26.20	3.276	22.59	2.824
9	29.87	3.319	25.47	2.830

UMR = unilateral medial rectus; PD = prism diopter.

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