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Corneal topographic astigmatism (CorT) and total corneal power

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Session Details

Session Title: Corneal Astigmatism Assessment. Surgery Equipment

Session Date/Time: Saturday 05/09/2015 | 11:00-13:00

Paper Time: 11:18

Venue: Main Auditorium

First Author: : N.Alpins AUSTRALIA

Co Author(s): :    G. Stamatelatos   J. Ong                 

Abstract Details


To evaluate the performance of corneal topographic astigmatism (CorT) based on total corneal power measurements compared to simulated keratometry (Sim K).


NewVision Clinics, Melbourne, Australia


Total corneal power measurements and simulated keratometry obtained using CSO Sirius and CZM Atlas topography were analyzed. CorTs were created from total corneal power measurements and compared to Sim Ks using the ocular residual astigmatism (ORA), which quantifies corneo-refractive differences. A low standard deviation of the ocular residual astigmatism (ORAsd) indicates a low variability between corneal astigmatism and refractive cylinder. A low mean of the ocular residual astigmatism magnitude indicates a close correlation of refractive cylinder and corneal astigmatism and greater parameter reliability.


The CorT based on total corneal power measurements had an ORAsd of 0.30 D and a mean ORA magnitude of 0.53 D, and was calculated by using measurements from a corneal annulus of 2.0 – 5.2 mm in diameter. The simulated keratometry had an ORAsd of 0.35D and a mean ORA magnitude of 0.70D. The ORAsd for CorT was significantly less than the Sim K measure of astigmatism (p <0.001).


The CorT based on total corneal power measurements corresponds better, both in variability and closeness, with manifest refractive cylinder than the Sim K based on a single Placido ring on topography. This total CorT provides a more valuable corneal parameter for toric IOL and femto/LRI surgery with further consistency for the effect of posterior corneal power on total corneal astigmatism.

Financial Interest:

One of the authors gains financially from product or procedure presented

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