Learning Curve for Strabismus Surgery

Jang Hun Lee; Sang Beom Han; Seung Jun Lee; Moo Sang Kim

doi:10.3341/jkos.2015.56.7.1111

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Lee, Han, Lee, and Kim: Learning Curve for Strabismus Surgery

Original Article

J Korean Ophthalmol Soc 2015;56(7):1111-1116.

Published online: 27 August 2015

DOI: https://doi.org/10.3341/jkos.2015.56.7.1111

Learning Curve for Strabismus Surgery

Jang Hun Lee, M.D, Sang Beom Han, M.D, Seung Jun Lee, M.D, Moo Sang Kim, M.D

Department of Ophthalmology, Kangwon National University School of Medicine, Chuncheon, Korea

Address reprint requests to Moo Sang Kim, MD Department of Ophthalmology, Kangwon National University Hospital, #156 Baengnyeong-ro, Chuncheon 200-722, Korea Tel: 82-33-258-2014, Fax: 82-33-251-0374 E-mail: kimmoo-79@hanmail.net

Received 21 November 201413 February 2015 Accepted 26 May 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.

Abstract

Purpose:

In the present study, we evaluated the learning curve of strabismus surgery performed by a single surgeon.

Methods:

We reviewed the data of 62 patients with exodeviation who underwent strabismus surgery and were followed up for at least 3 months between March 2011 and November 2014. Patients were divided into 3 groups classified chronologically and the success rate in each group was investigated. Additionally, the results of exotropia surgery were analyzed using cumulative sum (CUSUM) analysis. We compared 5 m distal angle deviation preoperatively and 3 months after strabismus surgery.

Results:

The overall surgical success rate of 62 patients was 72.6% (45/62). Success rates were 70% (14/20) in the first group, 71.4% (15/21) in the second group and 76.2% (16/21) in the third group. CUSUM analysis indicated that a surgeon’s perform-ance begins to improve at attempt number 11 and cumulative failure chart suggested the surgeon had achieved acceptable level of performance after 44 surgeries.

Conclusions:

A novice strabismus surgeon showed performance improvement after 11 cases and achieved acceptable level of performance after 44 strabismus surgeries. Although additional statistical data using more cases is needed, we suggest sur-geons should perform at least 50 strabismus surgeries to ensure a high success rate.

Keywords: Learning curve, Strabismus

References

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Figure 3.

Cumulative sum (CUSUM) chart for strabismus surgery. Blue line represent learning curve of surgeon. Upper and lower limits are represented by the lines h₀ (-1.855) and h₁(1.855). Line crossing h₀ from above indicate failure rates not significantly different from the acceptable failure rate.

Figure 1.

Success rates of strabismus surgery classified ^* p-values were calculated using chi-square chronologically. test.

Figure 2.

Cumulative failure (CF) graph of a series of 62 stra-bismus surgery by single surgeon from March 2011 to November 2014. CF acceptable rate set at 0.20, CF unacceptable failure rate set at 0.45. Type Ⅰ and Ⅱ error rates set at 0.10.

Table 1.

Formulas and values involved in CUSUM curve

Variables	Value
α^∗	0.1
β^†	0.1
ρ0	0.2
ρ1	0.45
P = ln ρ1/ρ0	0.811
Q = ln (1-ρ0)/(1-ρ1)	0.375
S = Q/(P+Q)	0.316
a = ln (1-β)/α	2.197
b = ln (1-α)/β	2.197
h = a/(P+Q)	1.855

CUSUM = Cumulative sum; ρ0 = acceptable outcome rate; ρ1 = unacceptable outcome rate.

^∗ Probability of a type I error;

^† Probability of a type II error.

Table 2.

Basal characteristic of subjects

	Group 1	Group 2	Group 3	p-value
No. (n, %)	20 (32.3)	21 (33.9)	21 (33.9)
Age (years)	42.9 ± 26.4	45.4 ± 27.7	45.4 ± 25.5	0.667^∗
Sex (M:F)	15:5	14:7	12:9	0.481^†
Diagnosis				0.219^†
Intermittent exotropia	9	15	13
Sensory exotropia	11	6	8
Mean deviation (PD)
Intermittent exotropia	31.7 ± 7.5	34.7 ±10.1	32.0 ± 11.5	0.696^∗
Sensory exotropia	35.0 ± 9.2	30.0 ± 6.12	29.3 ± 14.6	0.486^∗
Surgery type
R & R	18	11	8
Both LR recession	1	8	7
Single LR recession	1	2	6

Values are presented as mean ± SD unless otherwise indicated. R & R = resection and recession; LR = lateral rectus muscle.

^∗ p-values were calculated using one-way analysis of variance (ANOVA);

^† p-values were calculated using Pearson’s chi-square test.

Table 3.

Postoperative alignment of three groups

	Group 1	Group 2	Group 3	p-value
Undercorrected	6	6	4	0.815^∗
Corrected	14	15	16	0.251^∗
Overcorrected	0	0	1

^∗ p-values were calculated using chi-square test.

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