Repeatability of pyramidal aberrometer measurements in keratoconus and normal eyes

Abstract

PURPOSE: To evaluate the intrasubject repeatability of pyramidal aberrometer measurements in a sample of keratoconus and normal eyes. SETTING: American University of Beirut Medical Center, Beirut, Lebanon. DESIGN: Prospective comparative repeatability analysis. METHODS: Study Population: Keratoconus and Normal eyes from adult patients. Observation Procedures: Each eye was evaluated with 3 consecutive acquisitions using a pyramidal aberrometer. Main Outcome Measures: The repeatability of different ocular Higher Order and Lower Order Aberrations (HOAs and LOAs, respectively), and Zernike coefficients down to the fifth order, was evaluated. Repeatability was assessed by within-subject standard deviations (Sw), repeatability limits (r), and intraclass correlation coefficients (ICC), among other parameters. RESULTS: 72 keratoconus patients (72 eyes), and 76 normal patients (76 eyes) were included. In normal and keratoconus eyes, the ICC of total LOA and HOAs, as well as each of the Zernike coefficients, was >0.9. The Sw for keratoconus eyes with mean maximal keratometry (Kmax)<50D was 0.1345 for total LOAs, 0.0619 for total HOAs, 0.0292 for horizontal coma, 0.0561 for vertical coma, and 0.0221 for spherical aberration as compared to 0.2696, 0.1486, 0.0972, 0.1497 and 0.0757 for Keratoconus eyes with Kmax>=50D. Similar trend of better repeatability for grade 1 keratoconus and HOA<2D as compared to grade 2 and 3 keratoconus and eyes with HOA>2D were also noted. CONCLUSIONS: Ocular aberrometer measurements generated by high definition pyramidal aberrometers have high repeatability in both normal and mild keratoconus eyes; and moderate repeatability, yet still clinically acceptable, in advanced keratoconus. This is of particular importance in ocular wavefront-guided treatments.