Abstract
Purpose :
To evaluate whether the difference in asphericity or corneal spherical aberration (SA) would impact the IOL power and visual acuity (VA) for different ethnicities.
Methods :
A wide range of corneal asphericities for different ethnicities and geographic regions were reviewed based on published clinical information to develop schematic eye models for each ethnic cornea. Example of such ethnicities include Caucasian, African-American, Chinese, Indian, Japanese, Egyptians, Saudi-Arabian, Taiwanese, Tanzanian, Brazilian, and others. Separate model eye was developed for each of these ethnic populations to simulate and determine the SA at 6 mm pupil. First, a monofocal IOL was used to form an image on the retina to achieve emmetropia for the average corneal asphericity. The same emmetropic IOL power was setup in each ethnic model eye separately to determine the difference in power for the best focus. Subsequently, Modulation Transfer Function (MTF) and VA values were calculated for various amounts of defocus due to the difference in power.
Results :
The A-Constant value was obtained based on the SRK/T model eye with 0.28 µm SA to calculate the emmetropic IOL power of 20.754 D. The same IOL power was used to determine the difference in power for all other ethnic corneal asphericities. The results indicate a maximum IOL power difference of approximately +0.1 D from the average cornea to any of these studied ethnicities. For example, the IOL power differences are +0.099, -0.038 D, +0.023 D, +0.061 D, respectively for Japanese, Chinese, Egyptian and Indian populations. The photopic MTF and VA were calculated in the same schematic model eye with various amounts of defocus. The photopic VA is -0.033 logMAR at the best focus and -0.031 logMAR at 0.1 D of defocus.
Conclusions :
Based on our work, we conclude that recommendation of a different A-Constant is not required for individual ethnic populations as our calculated VA is above 20/20 in Log MAR values for all these differences in IOL power. The outcome of these findings can be helpful for surgeons to fine-tune the selection of IOL power for the potential cataract patients with different ethnic populations.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.