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Agreement of anterior corneal curvature assessment between placido topography and Scheimpflug topography in healthy and keratoconus eyes

Poster Details

First Author: S.Ortiz-Toquero SPAIN

Co Author(s):    V. Zuniga   V. De Juan   G. Rodriguez   D. Galarreta   R. Martin        

Abstract Details


Precise measurement of corneal curvature are of paramount important in different clinical situations, such as corneal refractive surgery patients management, keratoconus detection and follow up, phakic and pseudophakic intraocular lens calculation, and contact lens fitting. Nowadays, a great number of devices are available for corneal curvature assessment, including Scheimpflug or Placido-based topography, between others. The purpose of this study was to evaluate inter-device agreement between Placido topography (Allegro-Topolyzer; WaveLight Technologie AG [Alcon Laboratories], Erlangen, Germany) and Scheimpflug topography (Galilei-G4; Ziemer Group, Port, Switzerland) for the anterior corneal curvature assessment in healthy and keratoconus eyes.


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


112 eyes (56 healthy eyes and 56 keratoconus eyes) of 89 patients were included in the study. Corneal topography was assessed with Allegro-Topolyzer and Galilei-G4 in randomized order. Healthy subjects involve corneas without any ocular surface alteration (allergy, dry eye, ulcer, scar or other) and keratoconus patients were diagnosed after a complete eye-examination. Mean simulated keratometry (SimK), maximum (MaxP) and minimum (MinP) corneal power, astigmatism power and corneal astigmatism axis measured with both devices were collected. Agreement between both devices was evaluated using the Bland-Altman analysis, Pearson correlation coefficient, and paired t-test Student.


Allegro-Topolyzer underestimated all topographic values than Galilei-G4 (r<0.728 p<0.01) in both groups: healthy (p<0.05 in SimK, MaxP and MinP) and keratoconus (p<0.05 except MinP). Healthy eyes showed better agreement (SimK Diff -0.13±0.13, LoA -0.13 to 0.40; MaxP Diff -0.15±0.23, -0.30 to 0.59; MinP Diff -0.11±0.20, -0.29 to 0.51; astigmatism Diff -0.02±0.32, -0.60 to 0.64; and axis Diff -4.37±11.32º -17.81 to 26.56) than keratoconus eyes (SimK Diff -0.86±1.89, LoA -2.84 to 4.55; MaxP Diff -1.20±2.04, -2.80 to 5.21, MinP Diff -0.51±2.14 -3.68 to 4.70); astigmatism Diff -0.52±1.24, -1.90 to 2.95 and axis Diff 0.17±14.31º -28.22 to 27.89) in all topographic values.


Allegro-Topolyzer (Placido topography) underestimated anterior corneal topography values compared with Galilei-G4 (Scheimpflug topography) showing better agreement in healthy than keratoconus eyes. Hence, these instruments could be clinically used interchangeably in healthy eyes with caution, because statistical differences in SimK, MaxP and astigmatism were found in this study group. However, lower agreement and statistical differences found in keratoconus eyes, suggest that both devices cannot be used without distinction in keratoconus management, especially in keratoconus classification, although the magnitude of the difference could be clinically acceptable.

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