The Size and Change of Topographic Optic Zone after Laser In Situ Keratomileusis for Myopia：Comparison of Two Excimer Laser Machines
Date Issued
2005
Date
2005
Author(s)
DOI
zh-TW
Abstract
Purpose
To determine whether the optic zone matches what we have proposed, whether the optic zone is different with different excimer laser machines, what factors associate with the area of the optic zone, whether the optic zone changes or not as time passes and what factors associate with the change of the optic zone after myopic laser in situ keratomileusis (LASIK) surgery.
Setting
Department of Ophthalmology, National Taiwan University Hospital, Taipei, Taiwan
Methods
73 eyes out of 39 patients had myopic LASIK surgery with Summit laser machine and 27 eyes out of 15 patients with Allegretto were analyzed. The data include preoperative and 1-week, 1-month, 3-month and 6-month (Summit) postoperative subjective refraction and computerized videokeratography. Statistical analysis was performed to determine the difference of the area of the optic zone between the actual and the intended, the relationship between the optic zone and factors, such as the intended correction of spherical equivalent, the intended correction of the area of the optic zone, to compare the optic zone at different post-operative time, and to determine the relationship between the change of the optic zone and factors, such as the intended correction of spherical equivalent and the change of subjective refraction as time goes on.
Results
The actual optic zone does not match what we have proposed no matter what laser machine is. The actual optic zone is slightly smaller than the intended. (Summit: 88.69% +/- 13.69%, p<0.0001; Allegretto: 91.24% +/- 14.51%, p=0.0042).
In multiple linear regression model, there is correlation between the actual optic zone and the intended correction of the area of the optic zone (Summit : beta = -1.8453%, p<0.001；Allegretto: beta = -2.3697%, p<0.001) and the intended correction of spherical equivalent in these two laser machine (Summit : beta = 2.8721%, p<0.001；Allegretto: beta =3.8348%, p = 0.001) after adjusting age and gender. It means that the more intended correction of the area of the optic zone or the more intended correction of myopia, the less actual optic zone comparing with what we intended.
The actual optic zone becomes smaller and smaller when time goes by. The actual optic zone becomes stationary at post-operative 3 month with Summit laser machine and at post-operative 1 month with Allegretto (Summit: post-operative 1 month v.s. post-operative 1 week: -5.19% +/- 9.40%, p<0.001；post-operative 3 month v.s. post-operative 1 month:-3.79% +/- 8.01%, p=0.0001；post-operative 3 month v.s. post-operative 6 month：-0.73% +/- 9.12%, p=0.505 and Allegretto : post-operative 1 month v.s. post-operative 1 week: -5.045% +/- 9.22%, p=0.0087；post-operative 3 month v.s. post-operative 1 month: -1.39% +/- 7.02%, p=0.31).
In multiple linear regression model , there is no correlation between the optic zone change at different post-operative time and the intended correction of spherical equivalent in these two laser machines (Summit : post-operative 1 month : beta =0.3304%, p=0.457, post-operative 3 month : beta =0.2162%, p=0.662, post-operative 6 month : beta =0.6549%, p=0.392 and Allegretto : post-operative 1 month : beta =0.2011%, p=0.837, post-operative 3 month : beta = -0.2628%, p=0.839) after adjusting age and gender. There is correlation between the change of the optic zone and the change of subjective refraction at different post-operative time in these two laser machines. (Summit: post-operative 1-month：beta =10.3191%, p < 0.001；post-operative 3-month：beta =9.5676%, p < 0.001；post-operative 6-month：beta =8.1963%, p < 0.001 and Allegretto: post-operative 1-month：beta =5.1488%, p = 0.130；post-operative 3-month：beta =8.5942%, p = 0.008).
Conclusions
The actual optic zone is slightly smaller than what have proposed to treat. Though the actual optic zone with Summit is slightly smaller than that with Allegretto, there is no statistical significance. There is correlation between the size of the actual optic zone and the intended correction of spherical equivalent and the intended correction of the area of the optic zone in these two laser machines. It means that the more intended correction of the area of the optic zone or the more intended correction of myopia, the less actual area of the optic zone comparing with what we intended.
The reason why the optic zone takes more time to become stationary with Summit than Allegretto may be that Allegretto has a blend zone and Summit doesn’t. There is no correlation between the optic zone change at different post-operative time and the intended correction of spherical equivalent in these two laser machines. If the optic zone becomes smaller as time goes on, the patient will be more myopic.
Subjects
準分子雷射近視手術
光學區
電腦角膜地形分析圖
laser in situ keratomileusis
LASIK
optic zone
computerized videokeratography
myopia
Type
text
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