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Assessing the likely effect of posterior corneal curvature on toric intraocular lens calculation for IOLs of 2.5 dioptres cylinder power or more

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Session Details

Session Title: Pseudophakic IOLs: Toric

Session Date/Time: Tuesday 10/10/2017 | 08:30-10:30

Paper Time: 09:06

Venue: Room 4.4

First Author: : M.Goggin AUSTRALIA

Co Author(s): :    B. LaHood                    

Abstract Details


To establish if average refractive overcorrec¬tion or undercorrection of corneal astigmatism based on the “rule” of the astigmatism occurs if toric intraocular lenses (IOLs) are calculated on the basis of anterior cor¬neal measurements in eyes requiring toric IOL cylinder power of 2.5 Dioptres (D) or greater.



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



One hundred and thirteen consecutive eyes with anterior corneal keratometric astigmatism requiring IOL cylinder power of 2.5D or greater underwent phacoemulsification 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. Targeted and achieved astigmatic outcomes were compared. The main outcome measure was the post-operative refractive astigmatic prediction error.



A mean overcorrection occurred in anterior with-the-rule eyes of 0.16D (standard deviation (SD): 0.57D) and a mean undercorrection of against-the-rule eyes of -0.14D (SD: 0.53D). These were significantly different to the ideal value of zero (WTR p = 0.04, ATR p = 0.05). Though statistically significant, the effect size of these prediction errors were low at 0.4 for WTR and 0.36 for ATR and the mean error values are lower than 0.25D, which we would consider to be the minimum clinically significant error.



In eyes requiring and receiving toric IOLs of cylinder power of 2.5D or greater, an overcorrection occurs in anterior WTR eyes and an undercorrection in ATR eyes. Adjustment for this probable posterior corneal astigmatism effect could be applied. However the prediction error is not clinically significant, confirming that IOL cylinder powers are sufficiently accurately calculated using unadjusted anterior keratometry values in these eyes with greater anterior corneal astigmatism unlike eyes with lower anterior corneal astigmatism.

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