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Intrasubject repeatability of higher-order aberrations in healthy versus keratoconus eyes with Allegro-Topolyzer

Poster Details

First Author: G.Rodriguez SPAIN

Co Author(s):    R. Martin Herranz   S. Ortiz-Toquero   V. De Juan   D. Galarreta           

Abstract Details


Higher-order aberrations (HOAs) assessment is of utmost importance in current corneal refractive surgery performing custom ablations based on patient’s corneal topography. Besides, it assessment is relevant in the diagnosis and management of keratoconus and other ectatic conditions. Allegro-Topolyzer (WaveLight Technologie, Alcon-Laboratories, Germany) is a computerized Placido-based videokeratography especially developed for the clinical management of refractive surgical patients that allows data transfer to the WaveLight Excimer Laser systems and enables customized Topography-Guided treatments. The aim of this study was to determine and compare the repeatability of the anterior corneal surface HOAs provided by the Allegro Topolyzer in healthy and keratoconus eyes.


IOBA-Eye Institute, University of Valladolid (Valladolid, Spain).


Corneal topography of 36 healthy and 36 keratoconus eyes was assessed three consecutive times of each patient using the Allegro-Topolyzer. Repeatability of the 3rd- and 4th- order HOAs (coma, trefoil, spherical aberration, secondary astigmatism and tetrafoil) and RMS of coma-like (3rd-, 5th- and 7th- order), RMS up to 8th- order and RMS of HOAs were analyzed in 6.00 mm pupil diameter. Within-subject standard deviation (Sw), precision, repeatability, coefficient of variation (CV) and intraclass correlation coefficient (ICC) were calculated to determine and compare the repeatability. The mean value of the HOAs between healthy and keratoconus eyes were also compared.


All pair modals of Zernike coefficients were statistically different between healthy and keratoconus groups (p≤0.03). Healthy group shows Sw≤0.031 µm, CV between 6.49% (spherical aberration) to 37.18% (secondary astigmatism) and ICCs between 0.227 (7th- order RMS) to 0.982 (spherical aberration). Keratoconus group shows Sw≤0.059 µm, CV between 2.06% (HOAs Total RMS) to 25.82% (tetrafoil) and ICCs between 0.839 (8th- order RMS) to 0.996 (HOAs Total RMS).


Keratoconus eyes showed better repeatability of HOAs than healthy eyes measured with Allegro-Topolyzer. All HOAs, except in tetrafoil and RMS up to 7th- order showed good repeatability in keratoconus eyes. However, spherical aberration in healthy eyes is the most repeatable HOAs compared with the rest of Zernike coefficients who shows moderate and poor repeatability. These results could be of importance to eye care practitioners and refractive surgeons, who used HOAs assessment with Allegro-Topolyzer to support clinical decisions, because possible keratoconus detection is mandatory in pre-operative refractive surgery patients’ assessment.

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