Noise-floor benchmarking of surgically induced astigmatism after cataract surgery: anterior vs total keratometry.

PURPOSE: To determine how much of the measured surgically induced astigmatism (SIA) after cataract surgery reflects true surgical change vs measurement variability.

SETTING

Tertiary referral center.

DESIGN

Retrospective single-surgeon case series.

METHODS

Preoperative and postoperative corneal astigmatism was measured with an optical biometer (IOLMaster 700) using standard keratometry (K) and total keratometry (TK) values. SIA was calculated as the vector difference between postoperative and preoperative astigmatism. To estimate the contribution of measurement variability, a Monte Carlo zero SIA noise model was constructed using noise parameters calibrated against empirical repeatability from phakic eyes (σ = 0.12 diopters [D] for K; σ = 0.14 D for TK). Measured and simulated SIA distributions were compared using centroid analysis, cumulative distribution functions, and a Performance Efficiency Index (PEI).

RESULTS

324 eyes of 324 patients were analyzed for K and 269 for TK. Mean SIA magnitude was 0.38 ± 0.23 D (K) and 0.42 ± 0.25 D (TK). The observed centroids differed significantly from zero ( P < .001), indicating a systematic SIA component. The PEI was 88.8% for K and 89.4% for TK.

CONCLUSIONS

A substantial portion of measured keratometry-based SIA overlapped with the zero-SIA noise floor, leaving a modest systematic component. Noise-floor benchmarking helps contextualize SIA performance.