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B. Meinhardt, O. Stachs, A. Zhivov, R. Guthoff; Evaluation of Biometric Methods for Measuring the Corneal Thickness in Comparison to Confocal Laser Scanning Microscopic Investigations . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1333.
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© ARVO (1962-2015); The Authors (2016-present)
The exact determination of corneal thickness (CT) is an important component in preoperative diagnostics prior to refractive surgery and for intraocular pressure determination. For this reason a systematic investigation of the currently available methods for measuring the corneal thickness was undertaken.
In a prospective comparative study the central CT of 50 phakic eyes of 27 patients (age range 19 to 59 years) was measured with Scheimpflug Imaging (Pentacam, Oculus), Dual–beam partial coherence interferometry (AC–Master, Zeiss), slit–lamp pachymetry by Jaeger (Haag–Streit) and with optical slit scanning (Orbscan II, Orbtek). In addition AC–Master measurements were directly compared with in vivo confocal laser scanning microscopy (CLSM, Heidelberg Engineering). In all cases, at least three successive measurements were performed per eye, and a mean value calculated. To evaluate the precision of the instruments, the standard deviation was determined for ten successive measurements conducted by one examiner on one phakic eye. The Bland–Altman plot was used to reveal a relationship between the differences and averages.
The median CT values were 550 µm (Pentacam), 522 µm (AC–Master), 500 µm (Jaeger) and 536 µm (Orbscan II). The precision was ± 6.1 µm (Pentacam), ±1.7 µm (AC–Master), ±14 µm (Jaeger), ±8.9 µm (Orbscan II) and ± 6.0 µm (CLSM). The maximum method–dependent difference in CT determination was 50 µm. The median CT’s measured with the non–contact methods differed significantly (p=0.05, Wilcoxon and Wilcox). No significant difference was found between AC–Master (median 546 µm) and CLSM (median 560 µm).
All used methods allow a determination of corneal thickness, but the results might differ due to measuring principles inherent to the system, experience of the examiner and compliance of the patient. Jaeger and CLSM are less suited for clinical use, but CLSM is an excellent method for visualising corneal cell layers with high acuity. In the AC–Master a relatively high level of experience in the use of the instrument and a high degree of patient compliance are required. Nevertheless with the AC–Master, extremely precise measurements of the CT at the anatomic or optical axis can be made.
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