Measurements of central corneal thickness using two immersion ultrasound techniques and optical technique

Objective: To compare the accuracy of central corneal thickness measurements using ultrasound biomicroscopy, Orbscan II tomography and an Artemis-2 very high frequency ultrasound scanner.Methods: The prospective study was conducted at Eye World Centre, Riyadh, Saudi Arabia, from September to November 2012. One eye from each of 60 normal subjects was analysed. The central corneal thickness was measured using ultrasound biomicroscopy, Orbscan II tomography and the Artemis-2 very high frequency ultrasound scanner. Results were compared using analysis of variance, repeated-measures analysis of variance and limits of agreement.Results: The mean central corneal thickness was 530.30±30.75mm, 548.95±30.33mm and 554.73±31.97mm for biomicroscopy, tomography and the scanner respectively. The intraobserver repeatability analyses of variance were not significant for the three procedures (p=0.19, 0.23 and 0.41, respectively). A significant difference was noted among the three different methods (p=0.0001). However, comparison among instruments revealed no significant difference between tomography and the scanner (p 0.05), yet significant differences were noted in biomicroscopy vs. tomography, and biomicroscopy vs. the scanner (p 0.01 and P 0.001, respectively). The mean differences (and upper/lower limits of agreement) for central corneal thickness measurements were 18.92±40.71 (60.90/-98.70); 24.7±13.13 (1.00/-50.40), and -5.80±38.61 (69.90/-81.40) for biomicroscopy vs. tomography, biomicroscopy vs. scanner, and tomography vs. scanner respectively.Conclusions: The central corneal thickenss measurements obtained using Orbscan II tomography and the Artemis-2 very high frequency ultrasound scanner can be used interchangeably. However, Orbscan II tomography and the Artemis-2 scanner measurements cannot be used interchangeably with ultrasound biomicroscopy.