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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

Purpose:

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

Setting:

Dpt. of Ophthalmology, Goethe University, Frankfurt, Germany

Methods:

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.

Results:

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).

Conclusions:

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.

Financial Disclosure:

NONE

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