Repeatability and reproducibility of a new optical biometer in normal and keratoconic eyes

Purpose: To evaluate the repeatability and reproducibility of measurements obtained by a new optical biometer (Nidek AL-Scan) in normal eyes and keratoconic eyes.

Setting: Department of Ophthalmology, Turgut Özal University, Medical School, Ankara, Turkey.

Design: Evaluation of diagnostic technology.

Methods: To assess the repeatability and reproducibility of the optical biometer, 2 independent examiners performed 3 consecutive measurements. The following parameters were evaluated: central corneal thickness (CCT), anterior chamber depth, axial length (AL), corneal dioptric power in the flattest meridian (flat keratometry [K]) and in the steepest meridian (steep K), and white-to-white (WTW) distance. Repeatability was assessed using the within-subject standard deviation (S(w)), repeatability, and precision. Reproducibility was evaluated using the 95% limits of agreement proposed by Bland and Altman.

Results: Thirty healthy subjects and 27 patients with keratoconus were evaluated. Both examiners achieved high repeatability for all parameters in each group except for the steep K measurement in keratoconic eyes performed by examiner 2 (S(w) = 3.341). The WTW in normal eyes and the CCT and steep K in keratoconic eyes showed less repeatability. In both groups, the smallest range of agreement was in AL measurements whereas the largest was in CCT measurements. In keratoconic eyes, the range of agreement for steep K was also greater (3.766).

Conclusions: The precision of the measurements obtained by the new optical biometer was high.

Financial disclosure: No author has a financial or proprietary interest in any material or method mentioned.