Schimpflug versus Anterior Segment Optical Coherence Tomography after Epi-on Corneal Cross Linking in Keratoconus

Background: The measurement of corneal thickness is a crucial factor in evaluating keratoconus and its potential treatment methods, such as collagen cross-linking (CXL). The aim of this study was to evaluate the inter-device reliability in the corneal pachymetry following epi-on CXL using anterior segment optical coherence tomography (AS-OCT) and Scheimpflug tomography. Methods: This was across-sectional observational study that involved patients diagnosed with keratoconus and had undergone epi-on cross linking. Patients were subjected to follow-up examinations and corneal imaging with Pentacam (Oculyzer) and AS-OCT (Optovue). The inter-device reliability was assessed using the intraclass correlation coefficient (ICC) and Cronbach’s alpha. Results: 72 of eyes (36 patients), aged (18-43) years with 27 (75%) males, 9(25%) females were included in the study. Regarding central corneal thickness (CCT) pentacam measured a mean of 519.18µm, versus 507.83 µm using AS-OCT, P value < 0.001. Thinnest corneal thickness (TCT) measured 511.61µm with pentacam versus 491.61 µm using AS-OCT, P value <0.001. On evaluating the agreement between pentacam and AS-OCT in measuring central corneal thickness, ICC ranged from 0.82 to 0.984, which reflected excellent reliability. Cronbach alpha was 0.975 demonstrated excellent agreement. For TCT, ICC ranged from 0.15 to 0.979, which reflected good reliability. Cronbach alpha was 0.972 demonstrated excellent agreement. Conclusion: Based on the results of corneal pachymetry, after epi-on CXL, both AS-OCT and pentacam demonstrates comparable measurements with excellent inter-device reliability. However, it is worth noting that the pentacam appears to slightly overestimates the CCT and TCT.