Pachymetric measurements using 3 different methods for cross linked keratoconic corneas

Purpose: To compare corneal thickness using US pachymeter, Scirus, and OCT, evaluate agreement between them as well as determine the variation of each machine in pre- and post- crosslinking of keratoconic eyes. Patients and methods: In total, 50 eyes of 25 keratoconic patients before and after cross linking treatment were analyzed in this study. Pachymetry measurements were performed at center, inferior and superior temporal and nasal locations using US pachymeter, OCT and Scirus. One way ANOVA, intra-class correlation coefficient (ICC), coefficient of variation (COV) and Bland and Altman plots were used for statistical analysis. Results: The mean corneal thicknesses measured at center, ST, and IT before cross-linking and at center, ST, SN and IN after crosslinking was statistically different between pachymeters. The highest correlation coefficient was found to be between US and OCT at IT (0.868) before cross-linking and between US and OCT at center (0.826) and ST (0.801) after cross-linking. Poorest agreement prior to cross-linking was between Scirus and OCT at SN (0.211), and after cross-linking between US and Scirus at IT (0.003), between US and OCT (0.099) as well as and between US and Scirus (ICC = 0.098) at IT. Variation was negligible for OCT and maximal for US pachymetry before and after cross-linking. Conclusion: OCT displayed high agreement with ultrasound pachymeter and least variations in readings before and after crosslinking of keratoconous eyes. Hence it is recommended to use only OCT for pre-surgical evaluation and follow-up. However, replication of the results in larger sample size is needed. Keywords: Pachymetry; Keratoconous; OCT; Scirus US pachymeter; Corneal thickness; cross linking