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Influence of flap shape and hinge angle on opaque bubble layer (OBL) formation in femtosecond LASIK surgery for myopic astigmatism

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Session Details

Session Title: LASIK Outcomes I

Session Date/Time: Tuesday 16/09/2014 | 14:00-16:00

Paper Time: 15:20

Venue: Boulevard B

First Author: : H.Lin TAIWAN

Co Author(s): :    Y. Fang   C. Sun   C. Pu   Y. Chou     

Abstract Details


The aim of this study was to evaluate the effect of flap shape (horizontal oval shape vs round shape) and hinge angle (50 vs 60 degree) on the proportion of OBL by using the femtosecond laser in flap creation in LASIK surgery. There is still controversy about optimal hinge angle as well as flap shape in a femtosecond laser flap creation. Oval shape flap could be easier combined with a large hinge angle, which could reduce the OBL formation. However, little is known on whether the differences still exist if a large hinge angle is combined with a round shape flap.


Universal eye center, ChunLi, Taoyuan, Taiwan ROC


This retrospective study of 34 patients (68 eyes) underwent myopic LASIK surgery at Universal eye center between Aug 2013 and Oct 2013. The Intralase femtosecond laser (Abbott Medical Optic, Inc.) was used to create a flap with 90~100 microns thickness. All surgical procedures were videotaped. The images of OBL were captured at the end of flap creation in each patient. A multivariate linear regression analyses was applied.


Twenty-one female and 13 male patients participated in this study. Oval shape flap with 50 degree hinge angle was created in 21 eyes (group A); oval shape flap with 60 degree hinge angle was created in 25 eyes (group B); round shape flap with 50 degree hinge angle was created in 11 eyes (group C); and round shape flap with 60 degree hinge angle was created in 11 eyes (group D). The OBL covered a mean area of 10.3 +7.4%. The size of OBL were 12.7+7.6 % in group A; 8.4 +7.9% in group B, 12.5 +6.5% in group C and 7.6+5.1% in group D. The size of OBL was significantly less in eyes with a large hinge angle (p =0.0104). However, the flap shape (p= 0.1811) is not a significant factor affecting the size of OBL after controlling the hinge angle. Age (p=0.5241), sex (p=0.4017), corneal size=0.2668), cylinder power (0.3489), axial length (p=0.4002), intraocular pressure (p=0.4598), and central corneal thickness (p=0.3455) were not significant factors affecting the size of OBL.


In a femtosecond laser assisted lasik surgery, creation of the flap with a larger hinge angle could help reducing the size of OBL, however, oval shape flap is not superior to the round shape flap when hinge angle and other factors were controlled.

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