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Driving adoption and outcomes with toric IOLs: Pre-, intra-, and postoperative pearls for success by David R. Hardten, MD Preoperative tools and diagnostics: Pathways to improved treatment planning with toric IOLs Surgeons must manage astigmatism to achieve good uncorrected vision M ore than 70% of cat- aract patients have 0.5 D of astigma- tism or more before surgery. 1 It is crucial to recognize this and successfully manage astigmatism to provide the uncorrected vision our pa- tients seek. We have a number of tools at our disposal to help us reach this goal. These include corneal relaxing incisions and laser vision correction, but toric intraocular lenses (IOLs) are gaining popular- ity and offer an excellent means to correct very significant levels of astigmatism. Technologic necessities It is remarkable how many patients are referred to us after implantation of a toric IOL be- cause they are unhappy with their astigmatic results. Irregular astig- matism is one of the main reasons for residual astigmatism after implantation of a toric IOL. Irreg- ular astigmatism may result from previous RK or LASIK, anterior basement membrane dystrophy, dry eye, previous scars, and other conditions. Surgeons seeking good refrac- tive outcomes in their patients with astigmatism must determine the true astigmatic power of the cornea before surgery and predict how it will change after surgery. They also must verify whether astigmatism is regular. Toric IOLs feature a flat axis and steep axis, but they cannot correct for asym- metric astigmatism. Topography is necessary to verify that the astigmatism is regular; K readings are not sufficient. Regular astigmatism also may change if the incision is made in a slightly different location than in- tended. Furthermore, the internal incision or incision length can dramatically affect the amount of induced astigmatism. Surgeons should consider their average astigmatic result or customize their results. Surgeons must also be able to position the IOL correctly intraoperatively and examine and verify it after surgery. IOL misplacement or postoperative IOL rotation can result in residual astigmatism. We need to accurately mea- sure the primary curvature and verify that measurement. Tomog- raphy can be used to examine the anterior and posterior curvatures and understand the asphericity. This also can be accomplished empirically by nomograms of average asphericity and ratios of anterior and posterior corneal astigmatism. In addition, we can use a system that measures front and back, such as the Pentacam (Oculus, Arlington, Wash.) or the Galilei analyzer (Ziemer Ophthal- mic Systems, Port, Switzerland), which can measure total corneal curvature by subtracting the back curvature of the front of the eye. An accurate calculator and reliable alignment method are essential. The Barrett toric IOL calculator on the ASCRS website (www.ascrs.org/barrett-toric-cal- culator), which can be used for any toric IOL, can help surgeons estimate asphericity based on population averages (Figure 1). This formula also takes into consideration posterior corneal curvature and the lens position. Conclusion A number of low-tech tools are available to guide toric IOL im- plantation. We need to verify that the patient's topography shows regular astigmatism and be very wary of considering toric IOLs in patients with irregular astigma- tism. The irregularity creates an outcome that typically can't meet expectations of most patients when using toric IOLs, which only correct the regular component of the astigmatism. For optimal results, surgeons should use a high-quality calcula- tor that incorporates asphericity. They also should consider measur- ing it directly with a tomography system. Almost everyone has some degree of astigmatism that must be addressed. Our patients have high expectations. We need to make every effort to reduce astig- matism to less than 0.5 D. Reference 1. Hoffmann PC, Hütz WW. Analysis of biometry and prevalence data for corneal astigmatism in 23,239 eyes. J Cataract Refract Surg. 2010;36(9):1479–1485. Dr. Hardten practices with Minnesota Eye Consultants in Minneapolis. He can be contacted at drhardten@mneye.com. David R. Hardten, MD 4 Figure 1. Barrett calculator available at www.ascrs.org/barrett-toric-calculator

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