Ocular Parameters Influencing The Difference Between Standard And Total Keratometry In Routine Cataract Patients

Much is discussed about the difference between standard and total keratometry that is induced by keratorefractive surgery. However, small differences can be seen in patients without a keratorefractive history and there are no known associations between an increased difference in standard and total keratometry with other ocular parameters.

This study assessed the relationship between difference betweem standard vs. total keratometry and ocular parameters in patients attending cataract assessment clinics.

This was an observational study of consecutive patients attending cataract surgery clinic between October 2022 and October 2023. Data on age, axial length (AL), anterior chamber depth (ACD), anterior and posterior mean keratometry (Km), mean total keratometry (TK), white-to-white (WTW), central corneal thickness (CCT) and lens thickness (LT) were collected and patients with any warnings on the measurements were excluded. Pearson correlation between the difference between anterior Km vs. TK (Km vs.TK)  and rest of the ocular parameters was calculated. A stepwise backward multiple regression analysis was performed to identify a combination of ocular parameters strongly correlating to Km vs. Tk.

2448 eyes were included in the study. Positive associations were found with AL (r=0.051, p<0.05) and negative associations were found with age (r=-0.143, p<0.001), LT (r=-0.066, p<0.01) and WTW (r=-0.079, p<0.001). The relationship between ACD and CCT was not statistically significant (r=0.036, p>0.05 and r=0.100, p>0.05).

Multivariate analysis showed a more significant correlation with increasing AL, ACD and CCT and decreasing age, LT and WTW (r=0.27, p<0.001).

There is sometimes a difference in anterior Km and TK in patients presenting to cataract clinic but little is documented about these differences. We identify a number of weak but statistically significant factors associated with the difference. This difference should be acknowledged with the development of future keratometers, intraocular lens (IOL) formulas and our understanding of corneal optics.