Comparison of Changes in Corneal Biomechanical Properties before and After Photorefractive Keratectomy and Small Incision Lenticule Extraction

Background: Corneal biomechanics is the study of the mechanical properties and responses of the cornea to external forces. Two devices are currently available for characterizing the corneal biomechanical properties in a clinical setting; Ocular Response Analyzer (ORA) (Reichert, Buffalo, New York, USA) based on bidirectional applanation tonometry and Corvis -ST (Oculus Optikgeräte GmbH, Wetzlar, Germany) based on corneal deformation estimation using Scheimpflug imaging. Ocular response analyzer was used to assess corneal hysteresis (CH) and corneal resistance factor (CRF) to characterize changes in corneal biomechanics.

The other device is Corvis –ST which produces air pulse on the cornea then measures and records the movements using a high-speed Scheimpflug video camera in real time. It is highly sensitive and specific to differentiate healthy cornea from keratoconic one.

Aim: The aim of our study is to compare the changes in corneal biomechanical properties before and after PRK and SMILE.

Patients and Methods: This is a prospective comparative study and included 20 patients who had undergone PRK by Allegretto wave eye-Q device & 20 patients who had undergone SMILE by Visumax Ziess device.

Results: The significant difference between two groups at 6 months after surgery considering IOPb=0.027*. Integ. Radius=0.001*. SPA1=0.003*. This difference makes Femto SMILE better than PRK procedure for more stability of the corneal biomechanics and possibly lowers the incidence of postoperative ectasia.

Conclusion: According to CORVIS-ST for corneal biomechanical evaluation, the significant difference between two groups at 6 months after surgery considering IOPb=0.027*. Integ. Radius=0.001*. SPA1=0.003*. This difference makes SMILE better than PRK procedure for more stability of the corneal biomechanics and possibly lowers the incidence of postoperative ectasia.