Official ESCRS | European Society of Cataract & Refractive Surgeons

Anterior surface based keratometry compared with Scheimpflug tomography based total corneal astigmatism

Session Details

Session Title: Cataract 1
Session Date/Time: Friday 20/02/2015 | 10:30-12:30
Paper Time: 10:30
Venue: Sadirvan B
First Author: : T.Kohnen GERMANY
Co Author(s): :    B. Tonn   O. Klaproth           

Abstract Details


Description of total corneal refractive power (TCRP) astigmatism by ray tracing using a Scheimpflug tomographer.


Dpt. of Ophthalmology, Goethe University, Frankfurt, Germany


Analysis of Scheimpflug tomography measurements to determine 3mm-zone TCRP astigmatism (CATCRP) by ray tracing calculations, astigmatism in 15°-zone from simulated keratometry (CASim-K), anterior-surface astigmatism (CAant) and posterior-surface astigmatism (CApost). An analysis of changes with age was performed. The error produced by estimating CATCRP using CASim-K was calculated through vector analyses. The percentages of steep meridian aligned vertically, obliquely and horizontally of CAant and CApost were calculated.


3818 healthy, previously unoperated eyes were analyzed. The mean magnitude of CApost was 0.33 diopter (D). A vertically aligned steep meridian (60° to 120°) was found in 71.2% of eyes for CAant and in 88.8% for CApost. With increasing age, the occurrence of steep meridian aligned horizontally in CAant increased from 9.1% (age 20-29yrs) to 31.8% (70-79yrs), while vertical alignment decreased from 77.4% to 48.1%. Alignment of CApost mostly remained vertically (90.9% to 80.7%). When CAant is vertical, CApost is vertical in 97% and CASim-K overestimates total corneal astigmatism (mean 0.11 D ± 0.22).


Total corneal astigmatism is overestimated by When CAant is horizontal, 18% of CApost is horizontal and CASim-K underestimates (mean 0.26 D ± 0.31) total corneal astigmatism. The mean vector difference between CATCRP and CASim-K was 0.18 at 178° and exceeded 0.50 D in 9% of eyes. CASim-K in eyes with with-the-rule astigmatism and cannot be predicted safely in eyes that do not have with-the-rule astigmatism by anterior measurements only.

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