Evaluation Of Iol Power Calculation Accuracy In 120 Eyes With Prior Corneal Refractive Surgery: Impact Of Total Keratometry (Tk)

To evaluate the refractive predictability of IOL power calculation using Total Keratometry (TK) compared to standard keratometry (K) in patients with various types of prior corneal refractive surgery (CRS).

UM6P hospitals, Department of Ophthalmology.

This prospective study included 120 eyes of 60 patients with a history of CRS undergoing cataract surgery. The cohort was divided into three subgroups based on the initial CRS: post-myopic LASIK/PRK (n=84), post-hyperopic LASIK/PRK (n=20), and radial keratotomy (RK) (n=16). All preoperative biometry measurements were performed using the IOLMaster 700 (Carl Zeiss Meditec AG). IOL power was calculated using the integrated Barrett True-K TK formula (utilizing measured posterior corneal surface) and compared to the standard Barrett True-K (No History) and Haigis-L formulas. The primary outcome measures were the Mean Absolute Error (MAE) and the percentage of eyes +/- 0.50 D of the target refraction at 3 months postoperatively.

The overall MAE was significantly lower with the Barrett True-K TK (+/-0.38 D) compared to the standard Barrett True-K (+/-0.49 D, p < 0.01) and Haigis-L (+/-0.52 D). In the post-myopic laser group (n=84), the TK-based calculation achieved the highest predictability, with 78% of eyes within +/- 0.50 D. For the most challenging subgroup, post-RK eyes (n=16), the use of Total Keratometry significantly reduced the hyperopic shift, with 67% of eyes achieving the +/- 0.50 D target compared to only 40% using standard K-based formulas. No significant refractive surprises were observed in the post-hyperopic group (n=20) when using TK.

The integration of direct posterior corneal measurements through Total Keratometry (TK) on the IOLMaster 700 significantly improves IOL power prediction across all types of prior corneal refractive surgery. While "no-history" formulas using TK currently offer a superior and reliable clinical workflow, the integration of Artificial Intelligence (AI) and Ray-Tracing software (such as Okulix) holds potential to further refine these outcomes, especially in cases with highly irregular corneas where traditional vergence-based models reach their limits.