Introduction: Additional lenses implanted in the ciliary sulcus (AddOn) are one option
for permanent correction of refractive error or generate pseudoaccommodation in the
pseudophakic eye. The purpose of this paper was to model the power and magnification
behaviour of toric AddOn and to show the effect sizes with a Monte Carlo simulation.
Methods: Anonymized data of a cataractous population uploaded for formula constant
optimization were extracted from the IOLCon platform. After filtering out data with
refractive spherical equivalent (RSEQ) between −0.75 and 0.25 dpt and refractive cylinder
(RCYL) lower than 0.75, for each of the N = 6,588 records, a toric AddOn was calculated
which transfers the refraction error from spectacle plane to AddOn plane using a matrix-based
calculation strategy based on linear Gaussian optics. The equivalent (AddOnEQ) and
toric (AddOnCYL) power of the AddOn and the overall lateral magnification change and
meridional magnification were derived for the situations before and after AddOn implantation,
and a linear modelling was fitted for all 4 parameters. Results: RSEQ is the dominant
effect size in the prediction of AddOnEQ and overall change in magnification (ΔM),
whereas the lens position (LP), corneal thickness (CCT), and mean corneal radius (CPa)
play a minor role. In a simplified model, AddOnEQ can be estimated by 0.0179 + 1.4104
RSEQ. RCYL and corneal radius difference (CPad) are the dominant effect sizes in the
prediction of AddOnCYL and the change in meridional magnification (ΔMmer), whereas
LP, CCT, CPa, and RSEQ play a minor role. In a simplified model, AddOnCYL can be predicted
by −0.0005 + 0.0328 CPad + 1.4087 RCYL. Myopic eyes gain in overall magnification,
whereas in hyperopic eyes, we observe a loss. Meridional distortion could be in general
reduced to 35% on average with a toric AddOn. Conclusion: Our simulation shows that
with a linear model, the equivalent and toric AddOn power, as well as overall change
in magnification, meridional distortion before and after AddOn implantation, and the
reduction in meridional distortion, can be easily predicted from the biometric data
in pseudophakic eyes with moderate refractive error.
