July 2019
Volume 60, Issue 9
Open Access
ARVO Annual Meeting Abstract  |   July 2019
Population based adjustment of oblique anterior corneal astigmatism to allow for the likely effect of posterior corneal astigmatism for calculation of toric IOLs
Author Affiliations & Notes
  • Michael Goggin
    Ophthalmology, University of Adelaide, Adelaide, South Australia, Australia
  • Shira Sheen-Ophir
    Ophthalmology, The Queen Elizabeth Hospital, Adelaide, South Australia, Australia
  • Ben LaHood
    Ophthalmology, Eye Institute, Auckland, New Zealand
  • Footnotes
    Commercial Relationships   Michael Goggin, None; Shira Sheen-Ophir, None; Ben LaHood, None
  • Footnotes
    Support  None
Investigative Ophthalmology & Visual Science July 2019, Vol.60, 3691. doi:
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      Michael Goggin, Shira Sheen-Ophir, Ben LaHood; Population based adjustment of oblique anterior corneal astigmatism to allow for the likely effect of posterior corneal astigmatism for calculation of toric IOLs. Invest. Ophthalmol. Vis. Sci. 2019;60(9):3691.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : In cataract surgery, adjustment of toric intraocular lens (IOL) cylinder power to allow for the effect of posterior corneal astigmatism on the basis of population based observation of the likely effect of posterior corneal astigmatism is an accepted norm for with-the-rule and against-the-rule corneas. Oblique anterior corneal astigmatism is uncommon and no examination of this technique specifically in such cases has been published although we have suggested not adjusting such eyes, given this information deficit. Despite this deficit of knowledge, almost all online toric IOL calculators apply these population-observed adjustments in such eyes. The aim of this study is to establish if adjustment of toric IOL cylinder power is required to achieve targeted refractive astigmatic outcome in eyes with oblique anterior corneal astigmatism.

Methods : Retrospective review of refractive astigmatic outcome following crystalline lens replacement with a toric IOLs in consecutive eyes with oblique anterior corneal astigmatism (steep axis 300 to 600 or 1200 to 1500) not adjusted for the likely effect of posterior corneal astigmatism. Outcome measures: 1. prediction error of the IOL cylinder power based on vector analysis of the astigmatic refractive outcome in such eyes, 2. the astigmatic correction index and 3. the coefficient of adjustment for subsequent eyes.

Results : 53 eyes were identified with oblique anterior corneal astigmatism prior to cataract surgery or clear lens extraction. Toric IOLs were inserted using a 1.8mm, astigmatically neutral incision. The cylinder power of these IOLs was not adjusted from that calculated on the basis of anterior corneal astigmatism alone. Mean (SD) absolute astigmatic prediction error was 0.3D (0.39). Geometric mean astigmatism correction index was 1.02 (2% overcorrection) and geometric mean coefficient of adjustment was 0.98.

Conclusions : Eyes with oblique anterior corneal astigmatism should not be adjusted for the likely effect of posterior corneal astigmatism for toric IOL calculation. The calculated coefficient of adjustment suggests an adjustment in toric IOL astigmatic correction to achieve an ideal result that is below clinical relevance. Online toric IOL calculators should be changed to reflect this.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

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