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D. Huang, Y. Li; Mapping LASIK Flap Thickness With High–speed Optical Coherence Tomography . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1077.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To map LASIK flap thickness with a high–speed corneal and anterior segment optical coherence tomography (CAS–OCT) system. Methods: The CAS–OCT prototype operated at 1.3 micron wavelength, 17 micron FWHM axial resolution in cornea and 2000 a–scan/sec. The cornea is mapped with 8 mm radial lines (256 a–scans) on 4 meridians centered on the apex reflection. The map acquisition time is 0.5 second. Twenty seven eyes undergoing primary LASIK were studied. LASIK flap was created using either the Hansatome or the Intralase femtosecond laser. Intraoperative pachymetry was performed using a 50 MHz ultrasound (US) probe. The LADARWave system was used for ablation. Three OCT scans were done on each visit, 1 day and 1 week postoperatively. An automated algorithm was developed to process the OCT images and map flap thickness. The maps were divided into central (r<1mm), pericentral (r=1–2.5mm) and transitional (r=2.5–3.5) zones for analysis. Results:The flap interface is best detected in the pericentral zone (r=1–2.5mm). Interpolation is necessary in the central and transitional zones. The automated flap boundary detection was accurate in all eyes by visual inspection. The 1 week flap thickness measurements are reported below in microns. The central flap thickness in 8 Hansatome Z18 eyes was 148+/–17 (mean+/–SD) microns by OCT and 118+/–18 microns by US. In the 8 Intralase cases with 120 micron setting, it was 158+/–10 microns by OCT and 160+/–19 microns by US. Eleven cases with other depth settings were also analyzed. Regional analysis of flap thickness maps showed the flaps are significantly thinner in the central region compared to the transitional regions in both the Hansatome and Intralase groups. The repeatability is 7 microns (SD) in central and pericentral zones. Conclusions: We have developed a method for using high–speed OCT to map LASIK flap thickness postoperatively. The measurement is non–contact, rapid, and repeatable. Mapping provides more information than point and profile measurements previously demonstrated. This could be valueble for the planning of LASIK enhancement and characterization of microkeratome performance.
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