Ethnicity-Based Differences in Corneal Asphericity: Intraocular Lens Power Calculation, Image Quality, and Visual...

To evaluate whether differences in asphericity or corneal spherical aberration (SA) affect intraocular lens (IOL) power and visual acuity (VA) among different ethnicities.

Modeling and simulation study based on published clinical data.

Individual eye models were developed with corneas designed to represent different ethnicities, based on clinical study data, to simulate and determine SA for a 6-mm pupil. The study included Black, Brazilian, Chinese, Egyptian, Indian, Japanese, Portuguese, Saudi Arabian, Tanzanian, Taiwanese, and White population groups. Corneal SA ranged from 0.17 to 0.31 µm among different ethnic and age groups. Differences in power in model eyes with various ethnic asphericities were assessed using spherical SA60AT, Clareon CNA0T0 (-0.20 µm SA), and a monofocal aspheric IOL (-0.28 µm SA). Modulation transfer function (MTF) and VA were calculated at different defocus. Defocus was applied from -0.5 to 0.5 D, using 0.05 D intervals.

Emmetropic IOL power for CNA0T0 was 20.756 D based on the A-Constant and an SRK/T model with 0.28-µm SA. For all ethnicities with CNA0T0, the maximum IOL power difference was approximately -0.1 D when compared with an average cornea. For spherical IOL, MTF was 0.562 units at best focus and 0.529 units at 0.1 D defocus; VA was -0.028 logMAR at best focus and -0.023 logMAR at 0.1 D defocus. For aspheric IOLs, MTF was 0.604 units at best focus and 0.579 units at 0.1 D defocus; VA was -0.033 logMAR at the best focus and -0.030 logMAR at 0.1 D defocus.

The calculated A-Constants for CNA0T0 for different ethnicities ranged from 119.029 to 119.151. Based on the specific model eye generated from published clinical data for each ethnicity and using a spherical and two aspheric monofocal intraocular lenses, the use of a different A-Constant for different ethnic populations would not impact visual outcomes.