JAN 03, 2012
Cataract/Anterior Segment
This prospective study evaluated the biometric and keratometric repeatability and reproducibility of a new optical low-coherence reflectometer and keratometer, the Lenstar LS 900. The authors found it to be extremely precise, with results comparable to those of the leading optical biometers.
The Lenstar LS 900 is a noncontact optical reflectometer and keratometer that has been available for clinical use since 2009. It measures the axial dimensions of the eye in a single step. The technology is based on optical low-coherence reflectometry, with an 820-μm superluminescent diode. In addition to the axial length (AL), the unit allows the measurement of central corneal thickness, aqueous depth, crystalline lens thickness and white-to-white corneal diameter. A dual-zone automated keratometer analyzes the anterior corneal curvature at 32 reference points orientated in two circles at approximately the 2.3- and 1.65-mm optical zones. The keratometric readings are calculated using a 1.3375 index of refraction and include the flattest meridian, the steepest meridian and the minus astigmatic cylinder axis.
The authors took all of the above-mentioned biometric and keratometric measurements of the first eye of 37 patients preoperatively and repeated the measurements one month later before the second eye surgery.
Intrasession repeatability and intersession reproducibility were excellent with a very low coefficient of variation and high interclass correlation coefficients for all measured parameters. Bland-Altman plots show good correlation for axial length measurements (95% limits of agreement ranging from −0.056 to +0.04 mm), anterior chamber depth (−0.22 to +0.18 mm), crystalline lens thickness (−0.21 to +0.27 mm), corneal diameter (−0.28 to +0.24 mm), average keratometric readings (−0.56 to +0.47 diopters) and amount of astigmatism (−0.58 to +0.40 diopters).
The authors conclude that while a larger series will be necessary to confirm the high precision of the measured parameters, this instrument has proven invaluable at producing precise measurements of central corneal thickness, aqueous depth and lens thickness, which may be important elements for future IOL power calculation formulas.