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Repeatability of Anterior Curvature Metrics in Healthy and Keratoconic Eyes with a Portable Handheld Topographer

Fernández-Velázquez, Fernando José, OD1,2*

doi: 10.1097/OPX.0000000000001307
ORIGINAL INVESTIGATIONS

SIGNIFICANCE This is a prospective observational investigation that studies the repeatability of several outcomes obtained with the Keratron Scout in healthy and keratoconic corneas. In addition, we have been able to determine the “noise” values of the instrument, which can be very useful when evaluating possible progression in keratoconus (KCN).

PURPOSE The purpose of this study was to evaluate the repeatability of several anterior curvature metrics provided by a portable and handheld Placido disk–based topographer in healthy and keratoconic eyes.

METHODS One eye from 50 keratoconic patients and 50 eyes from healthy patients were included in this prospective observational study. Two consecutive sessions (with three scans per session) were performed, and the following parameters were analyzed with a Keratron Scout topographer: flat keratometry, steep keratometry, flat corneal axis, corneal astigmatism, and flat and steep asphericities. In addition, in the KCN cohort, indices derived from the Cone Location and Magnitude Index were also recorded. Intrasession (first session, all three measurements) and intersession (one measurement from each session, selected randomly) statistics were calculated. The following variables were calculated: within-subject standard deviation, coefficient of repeatability (R), coefficient of variation, and intraclass correlation coefficient (ICC).

RESULTS In healthy eyes, the intrasession and intersession ICCs were high (0.947 to 0.999), and for both flat keratometry and steep keratometry, the within-subject standard deviation was 0.08 and R was 0.24 diopters. Repeatability was slightly lower in the KCN group, but the ICC was greater than 0.95, whereas the R for flat keratometry was 0.41 diopters.

CONCLUSIONS The Keratron Scout provides repeatable measures for the studied metrics in healthy and keratoconic eyes.

1Centro Fernández-Velázquez, Madrid, Spain

2Robert Frith Optometrists, Gillingham, UK *profesionales@fernandez-velazquez.com

Submitted: November 21, 2017

Accepted: July 4, 2018

Funding/Support: The author has reported no funding/support.

Conflict of Interest Disclosure: There are no conflicts of interest for the author that could have influenced the results of this work.

Author Contributions: Conceptualization: FJF-V; Data Curation: FJF-V; Formal Analysis: FJF-V; Funding Acquisition: FJF-V; Investigation: FJF-V; Methodology: FJF-V; Project Administration: FJF-V; Resources: FJF-V; Software: FJF-V; Supervision: FJF-V; Validation: FJF-V; Visualization: FJF-V; Writing – Original Draft: FJF-V; Writing – Review & Editing: FJF-V.

© 2018 American Academy of Optometry