Analysis of differences between keratometric astigmatism and total corneal astigmatism measured by IOLMaster 700.

PURPOSE: To compare keratometric astigmatism (ΔK) and total corneal astigmatism (ΔTK) calculated by the IOLMaster 700 in cataract cases with regular corneal astigmatism ≥ 0.75 diopters (D).

METHODS

This study was a secondary analysis of a database of cataract patients who had undergone examination with IOLMaster 700 between May 2021 and March 2022 at Shanghai Eye Disease Prevention and Treatment Center. The Surgically Induced Astigmatism Calculator v2.1 was used to examine vector errors between ΔK and ΔTK. Subgroup analyses were performed based on ΔK axis, ΔK magnitude, age, gender, mean simulated keratometry (Km), and white-to-white corneal diameter (WTW).

RESULTS

In total, 580 eyes in 580 cases were included. The centroid values of ΔK and ΔTK were 0.28 D at 4° ± 1.55 D and 0.51 D at 4° ± 1.60 D, respectively. ΔTK (1.38 [1.02-1.85] D) was significantly larger than ΔK (1.25 [0.98-1.69] D) (P < 0.0001). The absolute value of the vector error between ΔK and ΔTK (|ΔTK - ΔK|) was 0.24 (0.18-0.31) D. Among groups categorized based on ΔK axis, the |ΔTK - ΔK| was markedly reduced in the with-the-rule (WTR) astigmatism group compared with other groups; ΔTK was starkly lower than ΔK in the WTR astigmatism group (P = 0.0006), while ΔTK was larger than ΔK in the against-the-rule (ATR) astigmatism (P < 0.0001). The |ΔTK - ΔK| increased with the magnitude of ΔK and with age. The difference between ΔK and ΔTK showed no correlations with gender, Km, and WTW (all P > 0.05).

CONCLUSIONS

A significant difference between ΔK and ΔTK obtained by IOLMaster 700 was found in cataract cases with regular corneal astigmatism ≥ 0.75 D. Such a difference was markedly reduced in the WTR astigmatism group. In contrast, this difference increased with the magnitude of ΔK and age. Moreover, this difference was not associated with gender, Km, and WTW.