Posters

Biomechanical susceptibility in post-LASIK ectasia

Poster Details

First Author: B.Lopes UK

Co Author(s):    A. Mohammadvali   J. Wang   R. Ambrosio Jr.   A. Elsheikh           

Abstract Details

Purpose:

To evaluate corneal material properties from patient that developed Post-LASIK ectasia and from patient that remained stable.

Setting:

University of Liverpool

Methods:

A finite element model (FEM) was built based on patient-specific preoperative data (tomography, axial length and IOP) and surgical parameters (flap and ablation profile). Surgery was performed in virtual environment and the corneal shape of the FEM was compared with the clinical post-operative tomographic exam. The corneal material properties were identified through inverse analysis method when the lowest error between the corneal shape obtained from the numerical model and the clinical exam was achieved.

Results:

Two cases considered in the "safe limits" of the procedure, with normal clinical and tomographic exam (BAD-D<1.2) were evaluated. The stable presented age of 27 years, CCT: 566µm, Flap Thickness: 100µm, Ablation depth: 97µm, RSB: 369µm and PTA: 34%. The ectasia case was 39 years old, CCT: 500µm, Flap Thickness: 98µm, Ablation depth: 98µm, RSB: 304µm and PTA: 39%. After the inverse analysis, the post-LASIK ectasia presented softer cornea than the stable case, beta (tangent modulus) 0.6 and 0.9, respectively. Mean reference values are 1.0 for normal and 0.5 for keratoconus.

Conclusions:

Altered corneal biomechanics was found in post-LASIK ectasia case with normal corneal preoperative exam. This result enlightens that biomechanical weakness can happen even with normal corneal shape. To further optimize refractive surgery screening, corneal biomechanical assessment can be used in adjunct to other clinical, surgical and shape derived parameters.

Financial Disclosure:

receives consulting fees, retainer, or contract payments from a competing company, research is funded, fully or partially, by a competing company