Thinner Corneas Limit Agreement Between Total and Standard Keratometry Measurements

Total keratometry (TK) and standard keratometry (K) demonstrate good agreement in eyes with high myopia, but there are greater differences between the 2 methods in eyes with thinner corneas, according to a 1-year study published in Eye and Vision. Two  intraocular lens (IOL) power calculation methods (XGBoost and RBF 3.0), combined with either the TK or K method, may provide better IOL power calculation in these patients, according to the report.  

Researchers included 103 eyes of 103 patients with high myopia (mean age 64.99 years, 52 women) who underwent uneventful cataract surgery and IOL implantation between December 2020 and August 2021. Patients underwent routine eye examination including best-corrected visual acuity (BCVA), central corneal thickness (CCT), anterior chamber depth (ACD), and axial length (AL) measurements. At 1 month after surgery, standard deviation (SD) of the prediction errors (PEs), and mean and median absolute error (MedAE) were calculated for all eyes. Researchers compared these values among 10 formulas, including XGBoost, RBF 3.0, Kane, Barrett Universal II, Emmetropia Verifying Optical 2.0, Cooke K6, Haigis, SRK/T, and Wang-Koch modifications of Haigis and SRK/T formulas, utilizing either TK or K values. 

Overall, good agreement was noted between the TK and K methods (mean difference −0.02 D; 95% CI, −0.23-0.18; ICC=0.997; P <.001). A greater difference between TK and K values was associated with thinner CCT (r= −0.212; P =.032). TK and K methods showed no differences in gauging refractive errors, the researchers note. 

Among the 10 formulas, the XGBoost, RBF 3.0 and Kane performed best when calculating SDs of PEs in both TK and K groups (H test, P <.05). In the TK group, the XGBoost was similar to the RBF 3.0 (P >.05), and both predicted lower MedAEs than other formulas (all P <.05). 

Investigators compared the percentage of eyes within ±0.25, ±0.50, ±0.75, and ±1.00 D of PE in both TK and K groups. In eyes within ±0.50 D of PE in the TK group, XGBoost demonstrated comparable percentages with RBF 3.0 (74.76% vs 66.99%). The values were 90.29% vs 87.88% for XGBoost and RBF 3.0, respectively, in eyes with ±0.75 D of PE. 

“In this study, we demonstrated that highly myopic eyes with thinner CCTs tend to have larger differences between TK and K methods, while the XGBoost enhancement calculator and RBF 3.0 formula, with either TK or K method, seemed to be the most promising options for IOL power calculation for this special population,” according to the researchers. “Since other IOL models have different geometries or optical zones, future studies will be needed to determine that these results are repeatable in other IOL models.”

Study limitations include the use of only 1 IOL model among participants.

Reference

Wei L, Cheng K, He W, Zhu X, Lu Y. Application of total keratometry in ten intraocular lens power calculation formulas in highly myopic eyes. Eye and Vis. Published online June 9, 2022. doi:10.1186/s40662-022-00293-3