Agreement between keratometry measurements obtained with full gradient topography and Scheimpflug tomography systems in pre- and postoperative LASIK eyes

Abstract

Purpose : To assess the agreement between keratometry measurements taken with a full gradient corneal topographer and a Scheimpflug corneal tomographer in eyes before and after LASIK surgery.

Methods : A retrospective analysis was performed of pre- and postoperative keratometry data from 24 eyes of 24 subjects who underwent LASIK correction of myopic refractive errors. The mean age of the subjects was 31.5 ± 7.6 years (range: 23 to 55 years) with slightly more females (58.3%) than males. Outcome measures comprised steep (K_s) and flat (K_f) keratometry, steep keratometry axis, mean keratometry (K_m), corneal astigmatism (C_a) and the J₀ and J₄₅ astigmatic components. Paired t-tests and Bland-Altman plots with 95% limits of agreement were used to evaluate the difference between measurements.

Results : The differences between the devices in all outcome measures were small and not clinically significant. For topography and tomography respectively, preoperative K_m values were 43.96 ± 1.55 D and 43.76 ± 1.40 D (p = 0.07) and postoperative K_m values were 40.20 ± 1.57 D and 39.80 ± 1.80 D (p = 0.01). For topography and tomography respectively, preoperative C_a values were 2.11 ± 1.38 D and 2.18 ± 1.60 D (p = 0.66) and postoperative C_a values were 0.95 ± 0.34 D and 0.83 ± 0.29 D (p = 0.09). J₀ values were 0.99 ± 0.63 D and 0.92 ± 0.69 D (p = 0.28) preoperatively and 0.43 ± 0.20 D and 0.37 ± 0.17 D (p = 0.09) postoperatively for topography and tomography respectively. J₄₅ values were 0.05 ± 0.41 D and 0.15 ± 0.50 D (p = 0.12) preoperatively and -0.02 ± 0.18 D and- 0.02 ± 0.18 D (p = 1.0) postoperatively for topography and tomography respectively. The 95% limits of agreement were slightly smaller for preoperative compared to postoperative measurements.

Conclusions : The full gradient topographer and Scheimpflug tomographer produced comparable keratometry measurements in pre- and post-refractive surgery eyes.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.