A particularly useful resource for calculating IOL power in a post–refractive surgery patient has been developed by Warren Hill, MD; Li Wang, MD, PhD; and Doug Koch, MD. It is available on the website of the American Society of Cataract and Refractive Surgery (ASCRS) (http://iol.ascrs.org/).
To use this IOL calculator, the surgeon selects the appropriate prior refractive surgical procedure and enters the patient data, if known (Fig 11-1). The IOL powers, calculated by a variety of formulas, are displayed at the bottom of the form, and the surgeon can compare the results to select the best IOL power for the individual situation. This spreadsheet is updated with new formulas and information as they become available and at this time probably represents the best option for calculation of IOL powers in post–refractive surgery patients.
Patients need to be informed prior to cataract surgery, however, that IOL power calculations are not as accurate when performed after refractive surgery and that additional surgery, such as surface ablation, LASIK, IOL exchange, or a piggyback IOL, may be required to attain a better refractive result despite maximum effort by the surgeon preoperatively to prevent such an outcome. It should be remembered that cataract surgery done after RK often induces short-term corneal swelling with flattening and hyperopic shift. For this reason, in the event of a refractive “surprise,” an IOL exchange should not be performed in these patients until the cornea and refraction stabilize, which may take several weeks to months. As corneal curvature does not tend to change as much when cataract surgery is done after PRK or LASIK, it may be possible to perform an IOL exchange earlier in these patients.
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