Biomechanical effect of corneal cross-linking (CXL) in fellow human corneas following SMILE or PRK in an ex vivo model for postoperative ectasia

Session Details

Session Title: Keratoconus & Secondary Ectasia

Session Date/Time: Sunday 15/09/2019 | 08:00-10:00

Paper Time: 09:21

Venue: Free Paper Forum: Podium 2

First Author: : E.Torres-Netto SWITZERLAND

Co Author(s): :    B. Spiru   S. Kling   F. Gilardoni   A. Lazaridis   W. Sekundo   F. Hafezi              

Abstract Details

Purpose:

Although currently rare due to more accurate preoperative evaluations and modern surgical techniques, iatrogenic ectasia remains a complication after refractive surgery. Small Incision Lenticule Extraction (SMILE) and photorefractive keratectomy (PRK) are superior in preserving corneal biomechanics when compared to flap-based procedures. However, ectasia has been reported following SMILE and PRK. Here, we evaluated the biomechanical effect of corneal cross-linking (CXL) in fellow human corneas following SMILE or PRK in an ex vivo model for postoperative ectasia.

Setting:

The study was conducted jointly by the Department of Ophthalmology of the Phillips University of Marburg (Marburg, Germany) and the Center for Applied Biotechnology and Molecular Medicine at the University of Zurich (Zurich, Switzerland).

Methods:

Twenty-six paired human corneas preserved in tissue culture medium and unsuitable for transplantation were equally divided into two groups: right and left corneas were treated with PRK and SMILE, respectively. Corneal thickness was measured in all eyes immediately before surgery. Then, using an extensometer, all corneas underwent stretching with two cycles of up to 9.0N to induce biomechanical weakening similar to postoperative ectasia. Finally, accelerated corneal cross-linking (CXL) was performed with 9mW/cm2 for 10 minutes (total fluence of 5.4J/cm2) in both groups. Elastic modulus was calculated through analysis by two-dimension stress-strain extensometry.

Results:

Following the accelerated CXL treatment, the ectasia-like corneas, pretreated with either PRK or SMILE, showed a mean effective elastic modulus of 17.28 [standard deviation = 5.28] MPa and 14.18 [standard deviation = 5.03] MPa, respectively. Both groups presented normal distribution, hence a parametric test was selected for statistical analysis. Although the elastic modulus in corneas previously subjected to PRK was higher, there was no significant biomechanical difference between both groups (p=0.093).

Conclusions:

Under similar conditions, both experimental groups - PRK followed by CXL or SMILE followed by CXL - achieved equivalent biomechanical stability when measured experimentally in ex vivo human fellow corneas. Our data suggest that in the event of postoperative ectasia, the biomechanical improvement achieved by corneal cross-linking may be similar regardless of whether the primary surgery was PRK or SMILE.

Financial Disclosure:

None