Evaluation of total corneal power measurements with a new optical biometer

To evaluate the repeatability and validity of total corneal power measurements (total keratometry [TK]) obtained with a recently introduced optical biometer (IOLMaster 700, Carl Zeiss Meditec AG) to a Scheimpflug device (Pentacam, Oculus).

Department of Ophthalmology, Ludwig-Maximilians-University, Munich, Germany.

Prospective randomized controlled trial.

The inclusion criteria were a corneal astigmatism of 3.00 diopters (D) or less, no previous ocular surgery, no known corneal irregularities, and no known dry eyes. All eyes were measured 3 times using the optical biometer and the Scheimpflug device. The results were statistically compared using Bland-Altman, within-subject SD, and astigmatism vector analysis.

Ninety-three eyes of 93 subjects were included. Overall, the repeatability of all eyes measured was 0.42 for standard K, 0.40 for TK, 0.45 for total corneal refractive power (TCRP), 0.43 for true net power (TNP), and 0.39 for simulated K. Bland-Altman analysis showed no significant difference between the optical biometer's TK compared with standard K and the Scheimpflug device's simulated K, TNP, and TCRP, the P value exceeding .05 in each case. A difference of >0.50 diopters between astigmatism measurements between TK and TCRP was found in 10 cases compared with standard K and TNP with 0 and 2 cases.

Repeatability of both devices was high, although measurements of meridian showed a great variability, suggesting that numerous measurements are needed to enhance accuracy. TCRP measurements between recently introduced TK and TCRP cannot be used interchangeably. Future studies are necessary to evaluate which measurement will result in a better outcome when respective measurements are used for toric intraocular lens calculations.