J Korean Ophthalmol Soc.  2011 May;52(5):524-530. 10.3341/jkos.2011.52.5.524.

Comparison of Flap Thickness Measured with Ultrasound Subtraction Method, Direct Method, and Optical Coherence Tomography

• Lee SH
• Lee JE
• Kim JY
• Kim MJ
• Tchah HW

• KMID: 2214570
• DOI: http://doi.org/10.3341/jkos.2011.52.5.524

Abstract

PURPOSE
To compare the flap thicknesses measured with the ultrasound (US) subtraction method, the direct method, and optical coherence tomography (OCT) in femtosecond laser-assisted LASIK eyes.
METHODS
The present study included 65 eyes of 37 patients who underwent femtosecond laser-assisted LASIK surgery. Flap thickness was measured intraoperatively using the direct and subtraction methods with US pachymetry and postoperatively using anterior segment OCT. Flap thickness measurements were compared among the three methods.
RESULTS
There was no significant difference between the flap thickness measured using the US subtraction method and OCT (p = 0.511). The flap thickness values obtained by these two different methods also correlated well with each other (gamma = 0.820, p < 0.001). However, flap thickness measured using the US direct method was significantly different (p < 0.001) with a low agreement value compared to the other two methods. Furthermore, the US direct method showed a lower measurement success rate compared to the US subtraction method (54% vs. 95%).
CONCLUSIONS
Flap thickness measured using the US subtraction method and OCT showed different values compared to that measured using the US direct method. Because of the lower measurement success rate and agreement value, the US direct method is not capable of being used in substitute for the US subtraction method.

Keyword

Anterior segment optical coherence tomography; Femtosecond laser; Flap thickness; Ultrasound pachymetry

MeSH Terms

Eye
Humans
Keratomileusis, Laser In Situ
Tomography, Optical Coherence

Figure

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  Figure 1. Postoperative flap thickness measurement with anterior segment optical coherence tomography.

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  Figure 2. Scattergram showing the correlation of flap thickness measured by ultrasound (US) subtraction method, US direct method, and optical coherence tomography (OCT). (A) Correlation between US subtraction method and US direct method. (B) Correlation between US subtraction method and OCT. (C) Correlation between US direct method and OCT.

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  Figure 3. Bland-Altman plots between each two measurement methods. The middle line is the mean and the lines on the side represent the upper and lower 95% limits of agreement (LoA). (A) Ultrasound (US) subtraction method and US direct method. (B) US subtraction method and optical coherence tomography (OCT). (C) US direct method and OCT.

Reference

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