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Comparing accuracy: total keratometry on the IOLMaster 700 with Goggin nomogram adjusted anterior keratometry

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Session Details

Session Title: Toric IOL Calculations & Alignment

Session Date/Time: Sunday 23/09/2018 | 08:00-10:00

Paper Time: 08:00

Venue: Room A5

First Author: : M.Goggin AUSTRALIA

Co Author(s): :    B. LaHood   S. Beheregaray                 

Abstract Details


The Goggin nomogram has been prospectively studied and validated as a precisely estimating the effect of posterior corneal astigmatism on total corneal astigmatism. Carl Zeiss Meditec has recently released a new keratometric measure in the IOLMaster 700, “Total Keratometry” (TK), which attempts to measure posterior corneal power and provides a measure of total corneal power. This study aimed to compare the accuracy of TK measurements with Goggin nomogram adjusted anterior keratometry (GNAK) to describe total corneal astigmatic power and axis.


The Queen Elizabeth Hospital, Adelaide, and the University of Adelaide, Australia


Patients had routine biometry performed using the IOLMaster 700 prior to undergoing cataract surgery with toric intraocular lens (IOL) implantation. This provided Total Keratometry (TK) values. Using anterior keratometry, the Goggin nomogram was applied to provide nomogram-adjusted anterior keratometry values (GNAK) which estimate total corneal power. The agreement between TK at GNAK was analysed.


46 eyes were available for analysis. Overall, median GNAK and TK values were not statistically significantly different to each other (p = 0.526). Median astigmatism was 1.10 Dioptres (D) (95% CI: 0.89D-1.32D) for GNAK and 1.19D (95% CI: 1.08D – 1.31D) for TK. This lack of significant difference remained in with-the-rule (WTR) and against-the-rule (ATR) subgroup analyses. Summated vector mean (SVM) analyses of GNAK and TK compared to vector calculated post-operative keratometry showed similar spreads of data for both GNAK (SVM: 0.14D at 1760) and TK (0.19D at 1610).


TK appears to be able to measure total corneal astigmatism to a similar accuracy within clinical and statistical significance as GNAK estimates. This indicates that it would be safe and reasonable to use TK data for planning of cataract surgery with toric IOLs.

Financial Disclosure:


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