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Y Li, R Shekhar, D Huang; Corneal Anatomic Changes after LASIK Measured by Arc-Scanning Optical Coherence Tomography and Ultrasonic Pachymetry . Invest. Ophthalmol. Vis. Sci. 2002;43(13):153.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To compare arc-scanning optical coherence tomography (OCT) and ultrasonic pachymetry for measurements of corneal anatomic changes after laser in situ keratomileusis (LASIK). Methods: Three instruments, an arc-scanning OCT prototype, a 50MHz ultrasonic pachymeter (US), and a 20MHz ultrasonic pachymeter, were used to examine 30 eyes from 17 patients who had LASIK surgery for myopia on pre-operative and follow-up post-operative days. 50MHz US was also used to record intra-operative flap thickness and ablation depth. OCT images were obtained by scanning 4-mm-long along the horizontal meridian on central cornea. We developed automated OCT image processing to locate corneal surfaces and the flap interface and profile the thickness of corneal layers. Results: Central corneal thickness (CCT) measured by ultrasound was slightly thicker than those measured by OCT (95% CI slope = 1.03-1.05 pre-op., 1.00-1.01 post-op.). Flap thickness detected by OCT agrees well with intra-operative US measurements (mean diff. +/- SD = 3 +/- 15 µm). OCT measurement agrees with programmed laser ablation depth (95% CI slope = 0.96-1.11) much better than ultrasound. Intra-operative ultrasonic pachymetry overestimated ablation depth (95% CI slope = 1.05 -1.36). Conclusion: OCT measurements of corneal anatomy closely agree with ultrasonic pachymetry. OCT may be more accurate based on close agreement with programmed ablation. OCT can be used to non-invasively measure flap thickness post-operatively.
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