Toric IOL Calculations Using Different Devices and Methodology
To compare different measuring devices in toric intra-ocular lens (IOL) calculations with and without posterior corneal curvature consideration.
Consecutive cases with a toric IOL implantation and preoperative measurements using optical biomety (IOLMaster-500 and Lenstar-LS900) and Scheimpflug Camera (Pentacam) were reviewed. Different methods were compared in a theoretic selection of a toric IOL: (1) anterior corneal astigmatism using the tree devices; (2) vector subtraction of the posterior corneal astigmatism measured by the Pentacam from anterior corneal measurements; (3) Scheimpflug Camera’s true net corneal power. A toric IOL astigmatic power and axis, aiming the lowest residual astigmatism, were selected according to each method. Based on manifest refraction > 1 month following surgery, simulated residual refraction was calculated for each method.
Fifty-eight eyes, of 48 patients, operated by two surgeons, were enrolled in the study. Using anterior corneal measurements with the IOLMaster, Lenstar and Pentacam, median residual simulated astigmatisms were: 0.65 diopter (D), 0.68D and 0.71D respectively. Combining posterior topography showed better results with median residual astigmatism of 0.49D, 0.50D, and 0.64D (p=0.004, p=0.001, p=0.184, respectively). Residual astigmatism with Pentacam’s total corneal power was 0.62D. Integration of the posterior surface curvature changed IOL toricity in 64%, 60% and 57% respectively, and changed the axis in more than 5° in 15% with all devices.
Accounting for the posterior corneal astigmatism reduces residual astigmatism compared with anterior cornea alone. Adjustment the IOLs alignment using vector analysis to include posterior astigmatism axis, further improves refractive outcomes.