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Calculating Intraopertive Lens Power In Cataract Surgery After Photorefractive Keratectomy

Calculating the intraoperative lens power for cataract surgery after photorefractive keratectomy (PRK) can be improved by using a corrected, refraction-derived keratometric value instead of the measured, preoperative value.

In a nonrandomized, retrospective clinical study, researchers in The Netherlands identified nine patients (15 eyes) who underwent cataract surgery after prior PRK to correct myopia. The medical records of both the laser and cataract surgery centers were reviewed.

Eight different keratometric (K) values, measured or calculated, were entered into three different intraoperative lens (IOL) calculation formulas. Those formulas included SRK/T, Holladay 1, and Hoffer Q. The actual biometry and IOL parameters were used to predict postoperative refraction, which was compared with the actual refractive outcome. Also, the relative underestimation of the refractive change in corneal dioptric power by keratometry after PRK was calculated.

In seven of 15 eyes, IOL exchange or piggybacking was performed because of hyperopia. Retrospectively, the most accurate K value for IOL calculation was found to be the pre-PRK K value corrected by the spectacle plane change in refraction. Use of the Hoffer Q formula would have avoided postoperative hyperopia in more cases than the other formulas. The mean underestimation of the change in corneal power after PRK varied from 42 percent to 74 percent, depending on the method of calculation.
Archives of Ophthalmology 2002;120:431-438. "Clinical and Theoretical Results of Intraocular Lens Power Calculation for Cataract Surgery After Photorefractive Keratectomy for Myopia"

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