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Study defines causes of astigmatic surprise after toric IOL implantation
Understanding the root causes of refractive cylinder surprises that manifest after toric IOL implantation can enable surgeons to choose appropriate surgical methods for each patient’s individual case, according to a study.
The experimental study set out to define these causes by using vergence formulas to bring all lens powers to the corneal plane. The refractive cylinder effect of rotating a toric IOL and demonstrating how prevailing astigmatism and various planning and surgical steps contribute to postoperative refractive cylinder were determined by double-angle vector diagrams.
Other than errors in measurement and IOL selection, factors that contribute to astigmatic surprises postop include variation in the astigmatic effect of a phacoemulsification incision, an inaccurately placed incision or an unintended orientation of the IOL.
Astigmatic surprises can also occur due to unexpected toric power.
“The toric power of the IOL at the corneal plane may differ from the expected toric power,” the study authors said. “This may be caused by the use of a non-optimized lens constant, by the settling of the IOL at a position different from the expected anterior-posterior location or because the IOL power differs from the labeled power by an allowable manufacturing tolerance.”
There may also be unexplained non-lens ocular residual astigmatism remaining after implantation, which could be caused by longstanding pre-cataract non-lens ocular residual astigmatism, tilt of the implanted IOL and changes in the patient’s subjective perception of astigmatic neutralization.
Disclosure: Alpins and Stamatelatos have a financial interest in Assort. Ong is an employee of Assort.