Analysis of Enhancement Rate According to Age after Refractive Surgery with Schwind Amaris

Wook Kyum Kim; Hun Yang; Eun Young Cho; Hee Sun Kim; Jin Kuk Kim

doi:10.3341/jkos.2013.54.2.224

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Kim, Yang, Cho, Kim, and Kim: Analysis of Enhancement Rate According to Age after Refractive Surgery with Schwind Amaris

Original Article

J Korean Ophthalmol Soc 2007;54(2):224-230.

Published online: 24 August 2007

DOI: https://doi.org/10.3341/jkos.2013.54.2.224

Analysis of Enhancement Rate According to Age after Refractive Surgery with Schwind Amaris

Wook Kyum Kim, MD^1,², Hun Yang, MD¹, Eun Young Cho, MD¹, Hee Sun Kim, MD¹, Jin Kuk Kim, MD^1,²

¹B&VIIT Eye Center, Seoul, Korea

²KAIST GSMSE, Daejeon, Korea

Address reprint requests to Jin Kuk Kim, MD B&VIIT Eye Center #3 Seocho-daero 77-gil, Seocho-gu, Seoul 137-856, Korea Tel: 82-2-590-2000, Fax: 82-2-501-6435, E-mail: bestjinkuk@bseye.com

Received 17 October 201123 May 2012 Accepted 2 January 2013

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

To evaluate the clinical effects of an automatic energy-lowering system in patients over the age of 28 years with Schwind Amaris laser platform by analyzing the enhancement operation rate according to age.

Methods

A total of 20448 eyes from 10224 patients who received a bilateral LASIK or LASEK operation with the Schwind Amaris laser platform between August 2007 and April 2011 in our clinic were included in the present study. The rate of enhance operation due to undercorrection was analyzed to determine whether the age affects the enhancement operation rate.

Results

There were a total of 17 enhancement operations. Fifteen out of 17 eyes who received the enhanced operation were above the age of 28 years (p=0.005). In multivariate analysis, patient age over 28 years (OR=6.75, CI 1.54-29.60, p=0.011), preoperative higher spherical equivalent (OR=0.56, CI 0.41-0.77, p=0.0004) and preoperative higher mean keratometric value (OR=1.38, CI 1.01-1.88, p=0.043) were significantly associated with a higher enhancement operation rate.

Conclusions

Surgeons should be aware that the amount of laser energy from Schwind Amaris laser platform is automatically reduced in patients above the age of 28 years. Therefore, the nomogram should be adjusted to reduce the enhancement operation rate for a specific age group, especially in patients with higher preoperative myopic errors and steeper cornea.

J Korean Ophthalmol Soc 2013;54(2):224-230

Keywords: Enhancement operation, LASIK, Nomogram, Schwind Amaris laser, Undercorrection

References

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Figure 1.

The distribution of 17 enhanced eyes according to age at operation. yrs = years.

Figure 2.

Comparison of linear cornea biomechanics change with age and stepwise auto adjustment of laser energy of Schwind Amaris. The lower triangle may explain relatively high enhancement procedure rate at this age range.

Table 1.

General characteristics of 20448 eyes of 10224 patients who received LASIK or LASEK operation with Schwind Amaris laser platform

Characteristics	Values (mean ± SD)
Characteristics	Age at operation (years)	28.7 ± 5.4
Preoperative spherical equivalent (diopters)	-4.01 ± 1.43
Preoperative K average (diopters)	43.26 ± 1.35
Preoperative IOP (mm Hg)	15.0 ± 2.8
Preoperative central cornea thickness (ym)	540.3 ± 29.3

Values are presented as mean ± SD.

Table 2.

Analysis of operation methods of 10224 patients who received LASIK or LASEK operation with Schwind Amaris laser platform according to age groups

Characteristics	Age at operation
Characteristics	≤27 years	≥28 years	Total
LASIK (number of patients)	3609 (35.3%)	4396 (43.0%)	8005 (78.3%)
LASEK (number of patients)	1065 (10.4%)	1154 (11.3%)	2219 (21.7%)
Total	4674 (45.7%)	5550 (54.3%)	10224 (100%)

Table 3.

General characteristics of 17 eyes of 11 patients who received enhancement procedure because of undercorrection within 1 year after LASIK or LASEK operation with Schwind Amaris laser platform

Characteristics	Values (mean ± SD)
Age at primary operation (years)	33.4 ± 4.6
Interval from primary operation to enhance (months)	5.1 ± 2.4
Spherical equivalent before primary operation (diopters)	-5.26 ± 1.94
Spherical equivalent before enhance (diopters)	-0.93 ± 0.41
Visual acuity before enhance (log MAR)	0.17 ± 0.09
Spherical equivalent after enhancement (diopters)	-0.32 ± 0.44
Visual acuity after enhancement (log MAR)	-0.1 ± 0.1

Values are presented as mean ± SD.

Table 4.

The analysis of primary operation method and age distribution of 17 enhanced eyes after LASIK or LASEK operation with Schwind Amaris laser platform

Characteristics	Primary operation method (Numbers of eyes)
Characteristics	LASIK	LASEK	Total
≤27 years	1 (5.9%)	1 (5.9%)	2 (11.8%)
≥28 years	10 (58.8%)	5 (29.4%)	15 (88.2%)
Total	11 (64.7%)	6 (35.3%)	17 (100%)

Table 5.

Enhancement procedure rate after LASIK or LASEK with Schwind Amaris laser platform according to age at primary operation

Characteristics	Enhancement (Numbers of eyes)			p-value*
Characteristics	Yes	No	Total	p-value*
≤27 years	2 (0.01%)	9346 (45.71%)	9348 (45.72%)	0.001
≥28 years	15 (0.07%)	11085 (54.21%)	11100 (54.28%)
Total	17 (0.08%)	20431 (99.92%)	20448 (100%)

*Chi square test was done. Expected count was more than 5.

Table 6.

Comparison of parameters between enhanced group and unenhanced group (enhanced group = 17 eyes, unenhanced group = 20431 eyes)

Preoperative data	Values (mean ± SD)		p-value*
Preoperative data	Enhanced group	Unenhanced group	p-value*
Spherical equivalent (diopters)	-5.26 ± 1.94	-4.01 ± 1.43	0.017
K average (diopters)	44.02 ± 1.30	43.26 ± 1.35	0.021
IOP (mm Hg)	15.73 ± 2.63	15.00 ± 2.78	0.28
Central cornea thickness (um)	537.4 ± 34.4	540.3 ± 29.3	0.69

Values are presented as mean ± SD.

*t-test was done.

Table 7.

Clinical characteristics associated with enhancement procedure rate in patients who received Schwind Amaris LASIK or LASEK

Clinical factors	Correlations with enhancement procedure rate
Clinical factors	Odd ratio	95% CI	p-value*
Age (year) ≤27 ≥28	6.75	1.54-29.60	0.0113
Preoperative SE	0.56	0.41-0.77	0.0004
Preoperative K ave	1.38	1.01-1.88	0.0431

SE = spherical equivalent; K ave = arithmetic mean of cornea power.

*Multiple logistic regression mothod.

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