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Role of percent tissue altered (PTA) on post-LASIK ectasia in eyes with suspicious topography

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Session Details

Session Title: LASIK II

Session Date/Time: Tuesday 08/09/2015 | 14:00-16:00

Paper Time: 15:09

Venue: Room 10

First Author: : M.Santhiago BRAZIL

Co Author(s): :    D. Smadja   S. Wilson   R. Krueger   J. Randleman           

Abstract Details


To investigate the association of the percent tissue altered (PTA), with the occurrence of ectasia after LASIK in eyes with suspicious preoperative corneal topography.


University of Sao Paulo, Sao Paulo, Brazil; Cole Eye Institute, Cleveland Clinic, Cleveland OH, USA; University Center Hospital of Bordeaux, Bordeaux, France; Emory University School of Medicine, Atlanta, Georgia, USA.


This retrospective comparative case-control study included 57 eyes with suspicious preoperative Placido-based corneal topography that developed ectasia after LASIK (Suspect Ectasia Group), 32 eyes with suspicious topography that remained stable for at least three years after LASIK (Suspect Control group), and 30 eyes that developed ectasia with bilateral normal topography (Normal Topography Ectasia group). Groups were subdivided based on topographic asymmetry into High or Low Suspect groups. Preoperative central corneal thickness (CCT), residual stromal bed (RSB) and age (years) were also investigated in univariate and multivariate analyses.


Average PTA values for Normal Topography Ectasia (45), Low-Suspect Ectasia (39), High-Suspect Ectasia (36), Low-Suspect Control (32), and High-Suspect Control (29) were significantly different from one another in all comparisons (p<0.003) except High and Low-Suspect Ectasia groups (p=0.033), and presented the highest discriminative capability of all variables evaluated. Age was only significantly different between High-Suspect Ectasia and Normal Topography Ectasia groups, while CCT was not significantly different between any groups. Stepwise logistic regression revealed the PTA as the most significant independent variable (P < 0.0001), with RSB the next most significant parameter.


There remains a significant correlation between PTA values and ectasia risk after LASIK even in eyes with suspicious corneal topography. Less tissue alteration, or a lower PTA value, was necessary to induce ectasia in eyes with more remarkable signs of topographic abnormality, and PTA provided better discriminative capabilities than RSB for all study populations.

Financial Interest:

One of the authors travel has been funded, fully or partially, by a company producing, developing or supplying the product or procedure presented

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