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Adjustment of anterior corneal astigmatism values to incorporate the effect of posterior corneal curvature for toric IOL calculation

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Session Details

Session Title: Toric IOLs

Session Date/Time: Sunday 14/09/2014 | 16:30-18:30

Paper Time: 16:30

Venue: Capital Hall B

First Author: : M.Goggin AUSTRALIA

Co Author(s): :    L. van Zyl   K. Zamora-Alejo   A. Esterman        

Abstract Details


To establish if average refractive over or undercorrection of corneal astigmatism based on the “rule” of the astigmatism occurs if toric intra-ocular lenses (IOL) are calculated on the basis of anterior corneal measurements. To establish if any systematic over or undercorrection holds true throughout the dioptric range of toric IOL cylinders implanted. To calculate an adjustment that could be made for individual eyes to avoid this systematic error for toric IOLs subsequently implanted.


University Department and a publicly funded hospital in urban Australia


Data were collected on 143 consecutive eyes in 115 patients that had undergone 2.0mm micro-incisional phacoemulsification for cataract or refractive lens exchange with IOL powers calculated using anterior corneal curvature data alone. Eyes were grouped as either “with the rule” (WTR) or “against the rule” (ATR) on the basis of the steep anterior corneal meridian and targeted versus achieved astigmatic outcomes were compared between groups.


Significant prediction errors in astigmatic outcome occurred only with IOL cylinders of 2D or less where overcorrection occurred by a factor of 1.38 in WTR eyes and undercorrection by a factor of 0.65 in ATR eyes.


To improve outcome prediction in eyes undergoing toric IOL implantation of cylinders of less than 2D, a co-efficient of adjustment of 0.73 for WTR eyes and 1.53 for ATR eyes (the inverse of astigmatism correction indeces above) can be applied to the corneal astigmatism power value to calculate a more appropriate IOL cylinder power than that calculated by using unadjusted anterior corneal curvature measurements.

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