Corneal and Epithelial Thickness Measurements: Comparability between two Different Ocular Coherence Tomography Devices.

Background: Corneal and epithelial thickness maps obtained with high-frequency ultrasound were first used to diagnose keratoconus. Anterior segment OCT has recently become widely used in many conditions especially in preoperative planning before refractive surgery, keratoconus diagnosis, keratoconus progression monitoring, hydrops formation, and epithelial healing monitoring. We compare epithelial and pachymetric thickness-based parameters from two different Fourier-domain optical coherence tomography (OCT) devices as to whether they can be used interchangeably.

Methods: Retrospective, comparative chart review. This study comprises 24 normal consecutive eyes and 32 consecutive post-SMILE eyes with corneal thickness and epithelial thickness maps obtained using two different OCT devices (Cirrus 5000, Carl Zeiss Meditec, Germany and Avanti RTVue 100, OptoVue Inc., USA). The following common parameters in the print-out of the two OCT devices were examined: minimum corneal thickness (Pachy min), minimum corneal thickness minus median corneal thickness (Pachy min-med), average corneal thickness of the superonasal octant minus the average corneal thickness of the inferotemporal octant (Pachy SN-IT), average corneal thickness of the superior octant minus average corneal thickness of the inferior octant (Pachy S-I), minimum epithelial thickness (Epi min), and maximum epithelial thickness (Epi max).

Results: Pachy min and Epi max measurements matched well between the two devices (ICC at 0.906 and 0.839, respectively). We found a significant correlation in Pachy min (p = 0.040), Pachy min-med (p = 0.033), and Epi max (p < 0.001) in the normal eye group. Only Pachy min and Epi max measurements (p < 0.001 for both) exhibited a significant correlation between the two devices in the post-SMILE group.

Conclusion: Anterior segment OCT is a valuable method for evaluating quantitative corneal and epithelial thickness measurements. However, measurements may differ between devices, and they should not be used interchangeably.