A theoretical retrospective study found that the percentage of eyes with <0.5 D residual refractive astigmatism after toric IOL implantation improved by 19% using a new vergence-based algorithm for power calculations versus the previous fixed-ratio algorithm.
This article was reviewed by Mark Packer, MD
The use of an advanced vergence-based algorithm to calculate power for the MX60T neutral aspheric monofocal toric IOL (enVista, Bausch + Lomb) significantly improved refractive outcomes when compared with a previous fixed-ratio algorithm, according to Mark Packer, MD.
Dr. Packer, president, Mark Packer, MD Consulting, Boulder, CO, described the new algorithm and presented findings from a theoretical study using historical data to compare predicted residual refractive error and astigmatism using the vergence-based algorithm versus the previous formula.
Unlike a fixed-ratio algorithm that assumes the toric power is always in the same place, the new formula takes into account the distance between the corneal plane and the IOL plane.
The new formula incorporates platform-specific inputs for surgically induced astigmatism (SIA) and posterior corneal astigmatism (PCA).
Dr. Packer reported that the outcomes analysis showed that the percentage of eyes predicted to have <1 D residual refractive error improved from 55% using the fixed-ratio algorithm to 74% with the vergence-based formula.
The percentage of eyes with residual refractive astigmatism ≤0.5 D also improved from 55% with the fixed-ratio algorithm to 74% using the vergence-based formula.
“The percentage of eyes predicted to be left with 0.5 D or less residual refractive astigmatism with the vergence-based formula approaches the value of 80% that has been reported using other toric IOL formulas that are vergence-based and take into account posterior corneal astigmatism,” said Dr. Packer. “While the new formula seems to achieve its goal in reducing residual astigmatism, it is important to continue this project because I think the results can be further improved.”