The IOL Master measures only the anterior corneal curvature and estimates the total corneal power by assuming a fixed relationship between the anterior and posterior corneal surface. The Pentacam measures both the anterior and posterior corneal surface and therefore calculates the true corneal power. The aim of this non-randomised prospective study was to assess whether the Pentacam equivalent keratometry readings (EKR) for three corneal diameter zones (2, 3 and 4.5mm) were significantly different to IOL Master 500 keratometry measurements. Forty-five consecutive patients undergoing routine phacoemulsification and intraocular lens implantation were included in the study. Each patient underwent measurements with the IOL Master and Pentacam prior to surgery. Postoperatively, for each Pentacam EKR and IOL Master measurement, the difference between the observed and expected refractive error was calculated using the Holladay 2 and SRK/T formulae. From this the mean absolute error of refraction (MAE, the distance of the mean refraction from zero) was calculated. The mean keratometric measurements were statistically different between the IOL Master and the Pentacam EKRs in the 2, 3 and 4.5mm zones. However, despite the difference in the keratometry readings, there was no significant difference between the MAE of the IOL Master, EKR 2, 3 or 4.5mm for both the Holladay 2 and SRK/T formulae.

Comparison of the Pentacam equivalent keratometry reading and IOL master keratometry measurement in intraocular lens power calculations.
Karunaratne N.
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Anjali Gupta

Birmingham and Midland Eye Centre, Birmingham, UK.

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