Official ESCRS | European Society of Cataract & Refractive Surgeons


Correction target for astigmatism in topography-guided ablation and toric intraocular lens exchange in eyes with coma-dominant corneal optics

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Session Details

Session Title: LASIK & PRK II

Session Date/Time: Monday 16/09/2019 | 14:00-16:00

Paper Time: 14:24

Venue: Free Paper Forum: Podium 3

First Author: : W.Zhou NORWAY

Co Author(s): :    A. Stojanovic                             

Abstract Details


To evaluate the influence of coma on subjective astigmatism (SA) and suggest guidelines for surgical planning of astigmatism correction in topography-guided corneal ablation and toric intraocular lens (IOL) exchange surgery in eyes with coma-dominated corneal optics.


Theoretical software- and vector analysis-based treatment simulations at Synlaser clinic in Tromsoe, Norway.


Twelve eyes with coma-dominant corneal optics and low lenticular astigmatism (LA) were selected. The astigmatism remaining after subtracting total (anterior and posterior) corneal astigmatism (TCA) and LA from SA, termed discrepant astigmatism (DA), was calculated and correlated to corneal coma. Refractive and topography data were used for simulated topography-guided surgery in seven eyes (group 1) and for simulated lenticular exchange surgery with toric IOL in five eyes (group 2). The estimated postoperative subjective astigmatism (EPSA) after correction of TCA or SA for each group was compared.


The axis and magnitude of DA correlated strongly with the axis and magnitude of coma. In group 1, where topography-guided ablation removed corneal higher-order aberrations (HOAs), astigmatism correction target based on TCA, rather than SA, led to less EPSA. In group 2, where removal of the crystalline lens did not affect corneal HOAs and their influence on SA, toric IOL correction target based on SA, rather than TCA, led to less EPSA.


The current study emphasized the importance of an analytical approach in surgical planning, when estimating the origin and relationship between the various components of ocular astigmatism. In eyes with coma-dominant corneal optics, DA appears to correlate with coma. In such eyes, if topography-guided treatment that removes corneal HOAs is used, correcting TCA instead of SA, appears appropriate, while correcting SA may be more appropriate in lenticular exchange surgery with toric IOLs, where HOAs remain untreated.

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