May 2004
Volume 45, Issue 13
ARVO Annual Meeting Abstract  |   May 2004
Online measurement of corneal flap thickness by means of optical low coherence tomography (OCT) during LASIK surgery
Author Affiliations & Notes
  • J.E. J. Carstens
    Ophthalmology, Städtisches Klinikum Dessau, Dessau, Germany
  • F. Fankhauser II
    Ophthalmology, Städtisches Klinikum Dessau, Dessau, Germany
  • Footnotes
    Commercial Relationships  J.E.J. Carstens, Schwind–eye–tech–solutions F; F. Fankhauser II, Schwind–eye–tech–solutions F.
  • Footnotes
    Support  Schwind eye–tech–solutions, Germany
Investigative Ophthalmology & Visual Science May 2004, Vol.45, 2780. doi:
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      J.E. J. Carstens, F. Fankhauser II; Online measurement of corneal flap thickness by means of optical low coherence tomography (OCT) during LASIK surgery . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2780.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract: : Purpose: To evaluate in a pilot study the variation of online non–contact corneal thickness measurements during LASIK surgery by means of optical low–coherence tomography (OCT) compared to conventional ultrasound pachymetry. Methods: In a protoype setup the diagnostic beam of an OCT pachymeter based on low–coherence reflectometry (Haag–Streit, Switzerland) has been linked into the optical path of the observer microscope of an ESIRIS excimer laser (Schwind, Germany). In ten eyes of seven patients, undergoing topography–guided LASIK for myopic astigmatism, corneal thickness has been measured online before and after flapcut as well as after lifting of the flap. The cut has been performed with an Amadeus microkeratome (AMO, Germany). The intended flap thickness was 140 µm. The online measurements were compared to ultrasound pachymetry data obtained preoperatively. Results: The mean preoperative corneal thickness measured by ultrasound pachymetry was 547 +/– 21.71 µm, compared to 506 +/– 47 µm measured with the OCT device. The flap thickness determined by OCT was 149 +/–21.92 µm. The intraindividual standard deviations of the OCT data ranged from 3 to 112 µm. Conclusions: Variations of flap thickness produced by different microkeratomes are known to be between 5 and 25 µm. In vitro precision of corneal OCT measurements is described to be between 1 and 5 µm with high reproducibility. The data of the prototype setup used show significantly higher standard deviations. Two factors were identified as probable causes: 1. There was a discrete excentricity of the OCT beam projection in relation to the optical axis of the microscope. 2. The optical paths of the OCT and the observer were not coaxial, resulting in defocus of the OCT. These problems were due to design deficiencies of the optical link between the two systems and are to be solved by a modified design. Online optical pachymetry using OCT seems to be a promising non–invasive tool to measure corneal thickness during LASIK surgery.

Keywords: cornea: clinical science • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • refractive surgery: LASIK 

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