KEY POINTS
- This medical-physics simulation study developed a paraxial vergence-based framework for determining the optimal rotational adjustment of misaligned toric supplementary intraocular lenses, including both phakic lenses and secondary sulcus-fixated AddOn lenses.
- The calculation uses routinely obtainable inputs: manifest spectacle refraction, corneal power or curvature, labelled spherical-equivalent and toric lens power, measured lens axis, and axial lens position. Thin- and thick-cornea models can both be incorporated.
- Effective lens position was corrected for the difference between the lens back-vertex plane and image-side principal plane. Because modern commercial lens geometry is generally undisclosed, the authors used legacy phakic-lens patent data and custom template lens designs to model this offset.
- Four representative scenarios were tested: myopic phakic astigmatism, hyperopic phakic astigmatism, an AddOn lens after penetrating keratoplasty and cataract surgery, and an AddOn lens after previous myopic laser vision correction.
- The predicted optimal rotation ranged from approximately 16.3° to 18.4°. Absolute reductions in residual refractive cylinder ranged from 1.74 to 2.35 D, corresponding to relative improvements of 66.7% to 94.2%.
- In the strongest worked example, a 16.8° clockwise rotation was predicted to reduce residual cylinder from −2.5 D to approximately −0.15 D, a 94.2% reduction. In another example, an 18.4° counter-clockwise adjustment reduced cylinder by approximately 2.3 D.
- The framework explicitly discloses its optical assumptions and calculations, allowing independent implementation. However, commercially available lens geometry may differ from the modeled templates, paraxial optics may perform poorly with irregular astigmatism or higher-order aberrations, and none of the predicted rotations were prospectively tested in patients.
CLINICAL TAKEAWAY
The model provides a transparent way to estimate whether rotating a misaligned toric supplementary intraocular lens could meaningfully reduce residual astigmatism before undertaking another procedure. The numerical results are promising but purely computational; prospective comparison between predicted and achieved postoperative refraction is required before routine clinical adoption.