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Optimized keratometry and total corneal astigmatism for toric intraocular lens calculation

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Session Details

Session Title: Presented Poster Session: Cataract Surgery Outcomes

Venue: Poster Village: Pod 1

First Author: : K.Næser DENMARK

Co Author(s): :    G. Savini              

Abstract Details


To identify the most accurate modality of keratometric astigmatism (KA) or total corneal astigmatism (TCA) for toric intraocular lenses (T-IOLs) calculation and to optimize corneal measurements in order to eliminate the residual refractive astigmatism.


G.B. Bietti Foundation IRCCS, Rome, Italy


We consecutively enrolled 64 eyes with a monofocal T-IOL. Preoperatively, a rotating Scheimpflug camera (Pentacam HR, Oculus) measured TCA through ray-tracing. Different combinations of measurements at 3-mm diameter, centered on the pupil or the corneal vertex, and performed along a ring or within it, were compared. KA was measured by the same Scheimpflug camera and a corneal topographer (Keratron, Optikon 2000). Astigmatism analysis was carried out with Næser’s polar value method. The optimal preoperative corneal astigmatism was back-calculated from the postoperative refractive astigmatism.


With both devices, KA overcorrected with-the-rule (WTR) astigmatism by 0.6 diopters (D) and undercorrected against-the-rule (ATR) astigmatism by 0.3 D. The lowest meridional error in refractive astigmatism (ERA) was achieved by the TCA pupil/zone measurement in WTR eyes (0.27 D overcorrection) and TCA apex/zone measurement in ATR eyes (0.07 D undercorrection). In the whole sample, no measurement allowed more than 43.75% of eyes to yield an absolute error in astigmatism power <0.5 D. Optimized astigmatism values increased the percentage of eyes with this error up to 57.81%, with no difference with respect to Barrett’s and Abulafia-Koch’s calculators.


Compared to KA, TCA improves calculations for T-IOLs, but optimization of corneal astigmatism leads to the most accurate results.

Financial Disclosure:


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