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Clinical and Theoretical Results of Intraocular Lens Power Calculation for Cataract Surgery After Photorefractive Keratectomy for Myopia
Monica T. P. Odenthal, MD;
Cathrien A. Eggink, MD;
Gerrit Melles, MD, PhD;
Jan H. Pameyer, MD;
Annette J. M. Geerards, MD;
W. Houdijn Beekhuis, MD
Arch Ophthalmol. 2002;120:431-438.
Objectives To describe the refractive results of cataract surgery after photorefractive
keratectomy (PRK) for patients with myopia, and to find a more accurate method
to predict intraocular lens (IOL) power in these cases.
Design Nonrandomized, retrospective clinical study.
Patients and Methods Nine patients (15 eyes) who underwent cataract surgery after prior PRK
to correct myopia were identified. The medical records of both the laser and
cataract surgery centers were reviewed.
Main Outcome Measures Eight different keratometric values (K values; measured or calculated)
were entered into 3 different IOL calculation formulas: 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.
Results In 7 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% to 74%, depending
on the method of calculation.
Conclusion The predictability of IOL calculation for cataract surgery after PRK
can be improved by using a corrected, refraction-derived K value instead of
the measured, preoperative K value.
From the Academic Medical Center, University of Amsterdam, and the
Diaconessenhuis, Leiden, the Netherlands (Dr Odenthal); the Rotterdam Eye
Hospital, Rotterdam (Drs Odenthal, Pameyer, Geerards, and Beekhuis); the University
Hospital St Radboud, Nijmegen (Dr Eggink); and the Netherlands Institute for
Innovative Ocular Surgery, Rotterdam (Dr Melles).
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