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A retrospective clinical validation study on the modelling of regression after PRK surgery

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Session Details

Session Title: Surface Ablations for Correction of Ammetropias

Session Date/Time: Tuesday 16/09/2014 | 08:00-10:30

Paper Time: 08:54

Venue: Auditorium

First Author: : R.Vinciguerra ITALY

Co Author(s): :    P. Vinciguerra   C. Roberts   H. Studer        

Abstract Details


After refractive surgery we induce a modification in the corneal shape aimed to persist over time. Nevertheless, corneal remodeling can induce regression of the intended correction and limit the optimal outcome of the procedure. The aim of this retrospective study was to validate a numerical model of post-surgical regression with long-term follow-up clinical data of PRK surgery.


Humanitas Clinical and Research Center, Rozzano, Italy.; Department of Surgical and Morphological Sciences, University of Insubria, Varese, Italy; The Ohio State University, Ohio, USA; Integrated Scientific Services, Port, Switzerland


Mathematical modelling of epithelial regression (Huang et al, Am J Ophthalmol 2003), including epithelial absorption, -migration, -generation, and -loss rates, was used to predict post-surgical corneal surface changes. Predicted changes were compared to clinical PRK follow-up data. Thirty myopic patients who underwent excimer ablation surgery with a post-operative high curvature gradient (CG) with up to 2000 days of follow up were included in this retrospective study.


Clinical data shows that surgically induced flattening, expressed as central curvature value, regressed from -8.19D±2.07(SD) in the first months after surgery (53 days±36) to -7.33D±1.71(SD) 2000 days postop. Whereas, mathematical modelling predicted a regression from -8.01D±2.15(SD) to -7.85±1.64(SD) 2000 days postop. Prediction accuracy for central curvature changes therefore was 0.16D±0.67(SD) right after surgery, and -0.53D±0.37(SD) 2000 days postop. Similarly, prediction accuracy for AvgK was 0.35D±0.60(SD) right after surgery and 0.51D±0.30(SD) 2000 days postop. For higher order aberration RMS the prediction accuracy was -0.0385micron±0.0629(SD) right after surgery and -0.0315micron±0.0104(SD) 1750 days after surgery.


Our results show that mathematical modelling of post-surgical epithelial regression is able to estimate remodeling after refractive surgery and predict possible regression of the intended correction, even 2000 days after the operation. These results confirm the literature findings that regression is due to abrupt changes in curvature, expressed as high CG. When the CG is high, the surface curvature modification remains in progress even months after the ablation. The proposed mathematical model, if implemented in the laser software, could permit to avoid regression after refractive surgery by planning an ablation profile that minimizes epithelial remodeling.

Financial Interest:

One or more of the authors... is employed by a forNONEprofit company with an interest in the subject of the presentation, One or more of the authors... receives consulting fees, retainer, or contract payments from a company producing, developing or supplying the product or procedure presented

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