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A. Pallikaris, B.F. Diakonis, G.A. Kounis, M. Tziraki; Central Corneal Thickness Measurements With Heidelberg Retina Tomograph II/Rostock Cornea Module, Artemis, and Ultrasonic Pachymeters . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1354.
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© ARVO (1962-2015); The Authors (2016-present)
To measure central corneal thickness (CCT) by using a confocal scanning laser microscope and a very high frequency (VHF) ultrasound, and compare this measurement to thickness determined by two conventional ultrasonic pachymeters (300A PacScan; Sonomed Inc., Corneo–Cage Plus; Sonogage).
CCT was measured three times with each modality in one eye of 8 normal subjects by an experienced examiner. Inward and outward scanning direction of the cornea with the confocal microscope were considered as individual measurements. Moreover, CCT was determined at the same vector location of each series of images of each subject for the VHF ultrasound. Measurements with the VHF ultrasound were scheduled first to avoid influence by the other modalities as a result of corneal flattening. The order of measurements by the other modalities and eye selection, however, was random. Prior to CCT measurements, the refractive error was measured with an autorefractometer. Differences in CCT of the various modalities were examined by using a repeated measures analysis of variance.
Mean CCT measured by confocal microscopy was 493.83 ± 42.91 and 489.25 ± 49.24 µm for the inwards and outwards scanning, respectively. There was no statistical significant difference between these two measurements (P=0.84). The mean CCT values as determined by the VHF ultrasound, the PacScan pachymeter, and the Corneo–Cage pachymeter were 498.33 ± 37.24 µm, 543.83 ± 46.18 µm, and 539.21 ± 43.96 µm, respectively. Highly significant differences in CCT were found between the outward scanning direction of the confocal microscope and the two conventional ultrasonic pachymeters (p<0.034) as well as the inward scanning direction of the confocal microscope and the PacScan pachymeter (p=0.034). All other differences were insignificant (p>0.052) even though more subjects will be examined.
The confocal microscope and the VHF ultrasound demonstrate a difference of the mean CCT measurements as compared to the conventional ultrasonic pachymeters. Nonetheless, either one of them permits a more comprehensive examination of the cornea as the confocal microscope allows the simultaneous observation of the cellular structures of the cornea while the VHF ultrasound permits a thickness analysis of the whole cornea. Morover, both of them allow the simultaneous measurement of epithelial and stromal thickness. Consequently, these differences are important when using either one of them for corneal examination after surgical interventions.
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