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Accuracy of IOL Calculation in Cataract Surgery after Penetrating Keratoplasty

Dietrich T., Seitz B., Langenbucher A., Viestenz A., Küchle M., Naumann G. O. H.,
Friedrich-Alexander-Universität, Augenklinik (Erlangen)

Purpose: In concomitant cataract and penetrating keratoplasty (PK), the sequential procedure is supposed to have a higher accuracy in calculation of the intraocular lens (IOL) power compared to the classic triple procedure. The purpose of this study was to evaluate the refractive results of cataract surgery (extracapsular extraction with implantation of a posterior chamber intraocular lens, CAT) in patients after penetrating keratoplasty.
Methods: Our retrospective study included 72 eyes of 65 patients: in 35 eyes (G1), all corneal sutures had been removed before cataract surgery (median time interval between PK and CAT 3.1 years), 37 eyes (G2) had remaining corneal sutures when biometry was performed and sutures were removed intra- or postoperatively (median time interval between PK and CAT 1.5 years). Mean age of the patients (65/67 years), mean target refraction (- 1.8 diopters, D), and mean follow-up interval after CAT (2.9/3.4 years) were comparable in both groups. The power of the implanted IOL, which had been calculated using the Haigis formula, varied from 0 to 34 D (median 19,5 D). Pre- and postoperatively, refraction, keratometry, and visual acuity were recorded. Major outcome measure of this study was the deviation of the spherical equivalent of the real refraction from the target refraction after CAT.
Results: In G1/G2 mean visual acuity increased from 0.23/0.16 preoperatively to 0.56/0.50. Mean deviation from target refraction was - 0.3 ± 2.2 D (- 4.95 to + 3.15 D) in G1 and - 0.4 ± 3.0 D (- 7.3 to + 7.25 D) in G2. After CAT the steepening of the cornea was significantly smaller in G1 (0.5 ± 1.6 D) than it was in G2 (3.3 ± 2.1D; p=0.003).
Conclusions: Although the mean deviation from target refraction is minimal after cataract surgery following PK, our results indicate a high level of variability. If corneal sutures have been completely removed before biometry, the accuracy of the IOL power calculation seems to be better.