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Corneal topographic astigmatism (CorT): a new measure of corneal astigmatism

Session Details

Session Title: Assessment of Astigmatism

Session Date/Time: Saturday 05/10/2013 | 11:00-12:30

Paper Time: 11:06

Venue: Main Lecture Hall (Ground Floor)

First Author: : N.Alpins AUSTRALIA

Co Author(s): :    G. Stamatelatos              

Abstract Details


Data received from multiple topography Placido rings is used to determine a corneal astigmatism parameter more representative of manifest refractive cylinder than other corneal measures currently available.


NewVision Clinics Melbourne, Australia


A retrospective analysis was performed on 504 virgin eyes assessed for laser vision correction measured between June 2009 and August 2011 using the Humphrey® ATLAS™ 9000. Corneal power at 100 points on 22 rings and Zernike coefficients from simulated corneal wavefront was obtained using the “Export for research” function. Simulated keratometry, manual keratometry, corneal wavefront, paraxial curvature matching and a new parameter known as CorT was calculated using the summated vector mean of topographic rings with adequate data and then compared for accuracy to the manifest refraction cylinder using the ocular residual astigmatism magnitude (ORA) and its variability (ORAsd).


CorT (ORA 0.62 +/- 0.33D) had better correlation with manifest refractive cylinder than manual keratometry (ORA 0.68 +/- 0.38D), simulated keratometry (ORA 0.70 +/- 0.35D), corneal wavefront (ORA 0.74 +/- 0.36D) and paraxial curvature matching (ORA 0.85 +/- 0.48D). The ORA magnitude and ORAsd for CorT was significantly less than the other measures of astigmatism (<0.001).


A method of determining corneal astigmatism that correlates best with manifest refractive cylinder can be calculated using a new parameter known as CorT. This CorT demonstrated a lower ORA and less variability compared with Sim K, manual K, corneal wavefront and paraxial curvature matching.

Financial Interest:

... gains financially from product or procedure presented

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