Comparison of Conventional Keratometry and Total Keratometry in Untreated Myopic Eyes and Eyes After Keratorefractive Lenticule Extraction (KLEx)

Abstract

Purpose: Aim was to evaluate the differences between conventional keratometry values and Total Keratometry (TK) before and after keratorefractive lenticule extraction (KLEx). Additionally, correlations with central corneal thickness (CCT) and other variables were assessed in this study.

Setting: University Eye Hospital Marburg, Germany.

Design: Retrospective exploratory comparative study.

Methods: K-values and TK-values of 98 eyes were measured using an IOL Master 700 before and after KLEx. Statistical analyses, including paired t-tests and Bland-Altman analyses, were performed to compare the two measurement methods. Correlations were analysed between changes in CCT, amount of laser vision correction, and differences in K- and TK-values after KLEx.

Results: Significant differences between K-values and TK-values were observed both pre- and postoperatively (p<0.0001). Bland-Altman analysis demonstrated preoperatively a bias of 0.07 D (95% CI bias: 0.049 to 0.090), while postoperatively, the bias was 0.427 D (95% CI bias: -0.474 to -0.38). A strong relationship between the amount of reduction in CCT and the difference between K- and TK-values after KLEx (R2 = 0.751, p < 0.0001) was revealed. Similarly, regression analysis showed a robust association between the amount of laser vision correction and the difference between K- and TK-values after KLEx (R2 = 0.788, p < 0.0001).

Conclusion: This study demonstrates that TK-values provide a more comprehensive assessment of corneal power, especially after KLEx, where changes in the posterior corneal surface become increasingly significant. The correlations suggest that patients with higher degrees of preexistent myopia or significant amount of laser ablation require special consideration in their refractive corneal assessments.

Keywords: Bland-Altman Analysis; Conventional Keratometry; Corneal Power; IOL Power; KLEx; Myopia; Total Keratometry; cataract surgery; keratorefractive surgery.