Toricity Ratio: Formal Analysis and Surgical Implications
Purpose
To present a rigorous theory of the toricity ratio that is independent of intraocular power formula used and demonstrate the surgical implications for astigmatic patients undergoing cataract surgery with toric IOL implantation.
Methods
A formal calculus of astigmatism with a rigorous definitions of toricity and toricity ratio is developed. Closed form expressions are derived in the limits of small and arbitrary astigmatism and compared to manufacturers’ values, previously published numerical data (in particular Savinni, Hoffer et al., JCRS 2013) and the prediction of surgical outcomes.
Results
Closed form expressions obtained are elegantly simple and can be used directly in computing toric IOL values. In average cases, values predicted by the theory coincide with those provided by manufacturers. In extreme cases the predictions made by recent literature are corroborated and some new insights are manifested. Surgical results on patients receiving toric IOLs can thus be improved.
Conclusion
A formal approach to toricity and toricity ratio yield a powerful analysis and useful computational and surgical tools that may benefit the astigmatic patient presenting for cataract surgery.