A Longitudinal Study of LASIK Flap and Stromal Thickness with High-speed Optical Coherence Tomography

Yan Li, Marcelo V. Netto, Raj Shekhar, Ronald R. Krueger, David Huang

Research output: Contribution to journalArticle

81 Scopus citations

Abstract

Objective: To assess corneal anatomic changes after LASIK with a high-speed corneal and anterior segment optical coherence tomography (CAS-OCT) system. Design: Cross-sectional observational study. Participants: Fifty-one eyes of 26 healthy persons undergoing LASIK. Methods: The CAS-OCT prototype operated at a 1.3-μm wavelength and 2000 axial scans/second. The corneas were scanned with a flap profile pattern (horizontal line, 512 axial scans) and a flap map pattern (4 radials, 256 axial scans each). Both patterns are 8 mm long and are centered on the corneal vertex. LASIK flaps were created using either a mechanical microkeratome (Hansatome; Bausch & Lomb, Inc., Rochester, NY) or a femtosecond laser (Pulsion; IntraLase Corp., Irvine, CA). Intraoperative pachymetry was performed using a 50-MHz ultrasound probe. Three OCT scans were obtained on preoperative and post-LASIK visits up to 6 months. An automated algorithm was developed to process the OCT images and to calculate corneal, flap, and stromal bed thickness profiles and maps. The profiles and maps were divided into central (diameter, <2 mm), pericentral (2-5 mm), and transitional (5-7 mm) zones for analysis. Main Outcome Measures: Corneal, flap, and stromal bed thicknesses as determined by OCT and ultrasound pachymetry. Results: The flap interface was best detected in the pericentral zone. One week after surgery, the repeatability of OCT flap and stromal bed thickness measurement was 2 to 7 μm by pooled standard deviation for zones inside a 5-mm diameter. The central flap thickness in 24 Hansatome eyes with a 180-μm setting was 143±14 μm by OCT and 131±17 μm by ultrasound. In the 8 IntraLase cases with a 120-μm setting, it was 156±11 μm by OCT and 160±19 μm by ultrasound. Eyes with other settings also were analyzed. There were small systematic changes in flap thickness up to 1 week and bed thickness up to 3 months. Conclusions: We have developed a method for using high-speed OCT to measure LASIK flap thickness after surgery. The measurement is noncontact, rapid, and repeatable. Profile and map measurements provide more information than point measurements previously demonstrated. This could be valuable for planning LASIK enhancement and characterizing microkeratome performance.

Original languageEnglish (US)
Pages (from-to)1124-1132.e1
JournalOphthalmology
Volume114
Issue number6
DOIs
StatePublished - Jun 2007

ASJC Scopus subject areas

  • Ophthalmology

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