LAUSR

PURPOSE Corneal elevation maps are widely used to screen refractive surgery candidates; however, they might be misleading in eyes with significant corneal decentration such as large angle kappa. In this study, the associations of angle kappa and Pentacam decentration indices with elevation maps were assessed in normal refractive surgery candidates. SETTING Salouti Cornea Research Center, Salouti Eye Clinic, Shiraz, Iran. DESIGN Retrospective observational study. METHODS In this research, the right eyes of 173 refractive surgery candidates were assessed. Data of front and back corneal elevation maps, keratometric data, decentration indices, and corneal astigmatism obtained by Pentacam HR system and angle kappa obtained by Orbscan IIz were extracted. Maximum elevation (or depression) for each of the 4 quadrants was recorded. Correlations of elevation values with angle kappa, Pentacam decentration indices, keratometry, and astigmatism were examined by Pearson correlation coefficient. 148 age and sex-matched cases with keratoconus grade one were selected as positive controls, and Pentacam variables were compared between the groups. RESULTS In normal refractive surgery candidates, the mean of angle kappa was 5.32 ± 1.36 (SD) degrees. Angle kappa had a positive correlation with front and back temporal elevations based on a best-fit sphere (BFS) (r=0.339, p=0.001; r=0.300, p<0.001, respectively). Front and back keratometric astigmatisms were positively correlated with front and back nasal and temporal elevations (r≥0.543, p<0.001) and negatively correlated with superior and inferior elevations (r≤-0.547, p<0.001). These associations no longer existed, when using best-fit toric ellipse (BFTE) for calculating elevation data. The thinnest-point vertex decentration was significantly associated with the back-temporal elevation (based on the BFTE) in both normal (r=0.311, p< 0.001) and keratoconus (r=0.190, p=0.021) eyes. CONCLUSIONS The current study showed that elevation maps obtained by the Pentacam system using BFS might be affected by both the large angle kappa and corneal astigmatism, confounding the preoperative assessment of refractive surgery candidates. Using BFTS as a reference for calculating elevation data should eliminate most diagnostic issues, and thus is encouraged in this context.