[Effect of applanation tonometry on precision of biometry measurements].

Background: The aim of this study was to investigate the effect of applanation tonometry on the accuracy of biometric measurements and the reproducibility of keratometric measurements.
Patients and Methods: In this clinical prospective study a total of 16 patients were enrolled who presented for cataract surgery on 30 eyes. Biometry measurements were made using an IOLMaster optical biometer before and 10 min after standard Goldmann applanation tonometry. Local anesthesia was achieved by administering one drop of fluorescein-stained oxybuprocaine 0.4%.
Results: The mean absolute difference of intraocular lens power for emmetropia was 0.31 ± 0.33 D (range -1.56 to +1.12 D) and the mean standard deviation for R1 and R2 (n=28 eyes) was 0.014 ± 0.013 mm before and 0.024 ± 0.021 mm after tonometry. This difference was statistically significant (t-test, p<0.01). Moderate to severe irregular corneal surfaces were noted in some cases after tonometry.
Conclusions: Local anesthesia and applanation tonometry reduced the accuracy of IOL power calculations with differences exceeding ± 1 D and the reliability of consecutive keratometry measurements decreased significantly. Therefore, it is advisable to perform biometry measurements at the very beginning of the preoperative examination.