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    Presbyopic IOLs changing game for astigmatic patients

    New options change conversation but not need for precision, careful planning

     

    Careful still counts

    While patient counseling has been simplified by the new IOLs, my approach to preoperative measurements and surgery really hasn’t changed. If anything, new information about the impact of posterior corneal astigmatism means there are now extra steps (and extra stakes) in the determination of the best IOL power.

    I rely on corneal topography to confirm the astigmatism is regular, verify the axis of astigmatism, and then use that axis to evaluate the keratometry measurements from other devices. It is a good idea to get multiple measurements of the magnitude and axis of astigmatism.

    I look for consistency among the measurements and agreement with the axis. I also rely on an anterior eye segment tomography system (Pentacam, Oculus) to incorporate data on the posterior cornea and its contribution to the overall magnitude and axis of astigmatism.
    Toric IOL calculations based on anterior corneal measurements can result in overcorrection in eyes that have with-the-rule astigmatism and undercorrection in eyes that have against-the-rule astigmatism,1 so it is important to choose a method for adjusting for posterior corneal astigmatism (PCA) power and orientation in one’s IOL calculations.

    Reitblat and colleagues provide an overview of different methods for adjusting for PCA.2 They compared five methods, including anterior corneal astigmatism with optical low-coherence reflectometry (Lenstar, Haag-Streit), the Baylor nomogram, a combination of anterior keratometry with posterior tomography using vector analysis, and two different measures available on the anterior eye segment tomography system, the true net power and total corneal refractive power (Figure 1).

    The authors found using a PCA adjustment method resulted in a change in the toric IOL calculation in 62 to 81% of cases, depending on the method used, and reduced the residual refractive error in up to 62% of eyes. Although vector analysis performed the best, any of these methods is better than ignoring PCA.

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