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Surgically-induced corneal astigmatism measurement error

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Session Details

Session Title: Cataract Surgery Outcomes / Femto

Session Date/Time: Monday 15/09/2014 | 08:00-10:30

Paper Time: 09:45

Venue: Auditorium

First Author: : C.Hamer UK

Co Author(s): :    N. Habib   H. Buckhurst   C. Purslow   P. Buckhurst     

Abstract Details


The precision of toric lens implant calculators is dependant in part upon the accuracy with which surgically induced corneal astigmatism (SIA) can be predicted. This study aims to investigate how measurement error alone, when assessing corneal curvature, can cause a false determination of SIA.


Plymouth University, Peninsular Allied Health Centre


One hundred healthy phakic subjects were assessed on two separate sessions. Corneal curvature was assessed on both visits using a manual keratometer, auto-keratometer, cone topographer, placido-disc topographer, Scheimpflug tomographer and merged placido-disc/scheimpflug topographer. Vector analysis was used to determine the pseudo-SIA caused by the intersession reproducibility of corneal measurements in the absence of surgery.


The pseudo-SIA resulting from instrument error was 0.54±0.48D for the manual keratometer, 0.31±0.29D for the auto-keratometer, 0.65±0.41D for the cone topographer, 0.44±0.54D for the placido-disc topographer, 0.30±0.38D for the Scheimpflug tomographer and 0.63±0.87D with the merged placido-disc/scheimpflug topographer.


The inherent error in corneal curvature measurement causes a significant amount of pseudo-SIA. This pseudo-SIA may prevent the accurate assessment of the actual SIA induced by cataract surgery especially in the case of micro-incisional surgery, which has a minimum effect on the cornea.

Financial Interest:

One or more of the authors... receives consulting fees, retainer, or contract payments from a competing company

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