Central corneal thickness measurement with a retinal optical coherence tomography device versus standard ultrasonic pachymetry

Purpose. To demonstrate the capability of a standard, commercially available optical coherence tomography device (originally designed to measure retinal thickness) to image the human cornea in vivo and to measure central corneal thickness (CCT) in normal and edematous corneas. The intrapatient precision and interpatient variability of this novel application was compared to standard ultrasonic pachymetry. Also, the correlation of both methods was investigated. Methods. CCT measurements using optical coherence tomography (OCT) and ultrasonic pachymetry (PACH) were obtained in 36 normal eyes and 16 eyes with corneal edema. Results. Direct in vivo imaging of the cornea and measurements of CCT by OCT could be performed in all eyes. In normal subjects, CCTOCT was 530 +/- 32 mum and CCTPACH was 581 +/- 34 mum. The two methods showed a highly significant correlation with a standardized regression coefficient of 0.988. The difference between both methods was constant over the range of CCT (mean difference, 49.4 +/- 5.9 mum) The mean intrapatient SD of CCT measurements was 4.90 mum and 4.96 mum for OCT and PACH, respectively. In patients with corneal edema, mean CCTOCT was 601 +/- 59 mum, and mean CCTPACH was 667 +/- 68 mum. The difference between the two techniques increased slightly with increasing corneal edema (mean difference, 66.9 +/- 10.9 mum). Conclusion. Imaging of the human cornea can be performed by a standard retinal OCT device, and OCT measurement of CCT shows excellent correlation to values obtained by PACH, giving similar readings separated by a constant difference. In corneal edema, the difference between the two methods is additionally increased, but continues to demonstrate excellent consistency.