Comparative Analysis Of Astigmatic Powers And Accuracies Of Toric Calculations Among The Combination Of Different Keratometries And Toric Calculators.

To compare astigmatic powers of anterior keratometry (K) and total keratometry (TK) measured with the swept-source optical biometer IOLMaster 700 (Carl Zeiss Meditec AG) and total corneal refractive power (RP) measured with the swept-source optical biometer CASIA 2 (Tomey), and to compare postoperative astigmatism prediction errors (PE) of toric calculations by these different corneal refractive powers.

Single-center retrospective study at Yukioka Hospital, Osaka, Japan

Preoperatively, K and TK were measured with IOLMaster 700, RP with CASIA2. The optimal toric intraocular lens (IOL) and alignment axis were calculated with Barrett toric calculator (TC) based on K and axial length measured with IOLMaster 700. The toric IOL (Clareon® Toric (CNA0T3-6; Alcon Laboratories, Inc)) was inserted using a Clareon® AutonoMe® injector (Alcon). The alignment axis was managed with the Callisto Eye (Carl Zeiss)  system. Preoperative astigmatic powers of K, TK, and RP were compared. Postoperatively, two other TC formulas were used for toric calculations: Barrett TK TC using TK, Holladay TC using TK, and Holladay TC using RP. PE by each calculation method was calculated with vector analysis and was compared.

The study comprised 189 eyes of 189 patients (age (years). mean±SD: 76.4±8.73). Astigmatism was significantly smaller in K (P=0.0066) and RP (P<0.0001) compared to TK (Tukey test). The centroid errors in PE of Barrett TC using K and Barrett TK TC using TK (0.134, 0.201 diopter [D] each) were lower than Holladay TC using TK and RP (0.326, 0.484D each), all of which were deviating towards the against-the-rule side. The absolute value of postoperative astigmatism PE was not significantly different between Barrett TC using K and Barrett TK TC using TK (P=0.8598), but all other 2-arm comparisons were significantly different, with Holladay TC using RP having the largest error (Tukey test).

RP and TK are different. Care should be taken with RP because it is prone to large errors towards the against-the-rule side in the calculation of toric IOLs.