Iol A-Constants And Differences In Power Calculation For Various Ethnic Populations With Different Corneal Asphericities

Calculation of IOL power is critical for achieving optimal postoperative refractive outcomes and patient satisfaction after cataract surgery. To assess whether differences in corneal spherical aberration (SA) affect IOL A-Constant, power selection, and visual acuity (VA) for different ethnicities.

Modeling and simulation study for IOL power calculation based on published clinical data; Alcon Research, LLC.

A wide range of corneal asphericities for different ethnicities across diverse geographic regions were reviewed based on published clinical data. Population groups included Black, Brazilian, Caucasian, Chinese, Egyptian, Indian, Japanese, Portuguese, Saudi Arabian, Tanzanian, and Taiwanese. Individual eye models were developed for each ethnic cornea to simulate and determine the SA at 6 mm pupil. The A-Constant values and IOL powers were then obtained for all ethnic corneal asphericities based on the respective eye model for each ethnicity. To assess the impact produced by differences in power, Modulation Transfer Function (MTF) and VA values were calculated for various amounts of defocus

The A-Constant value for a Clareon monofocal IOL was obtained based on the SRK/T model with 0.28 µm SA to calculate the emmetropic IOL power. The same IOL power was used to determine the difference in power for all other ethnic corneal asphericities. The A-constants ranged from 119.029 in a Taiwanese population to 119.151 in a Tanzanian population. The maximum IOL power difference compared with the average cornea was approximately −0.1D. Photopic MTF for both aspheric IOLs were similar; MTF was 0.604 at the best focus and 0.579 units at 0.1D defocus. Photopic VA for the aspheric IOLs with −0.2 and −0.28 µm correction was −0.033 logMAR at the best focus and −0.030 logMAR at 0.1D defocus.

Our findings based on published clinical data suggest that the use of a different A-Constant for Alcon monofocal IOLs for different ethnic groups would not impact visual outcomes. The outcomes, however, may provide additional information to the surgeons for achieving the optimal visual outcomes for diverse cataract patient populations.