Biomechanical profile of refractive surgery procedures

Abstract

AbstractThe impact of corneal biomechanics continues to be increasingly recognized as an integral part of refractive surgery outcomes. Corneal biomechanical properties are of major importance in laser refractive surgery and must be taken into consideration to reduce the risk for iatrogenic ectasia. Some in vivo corneal biomechanical alterations are possible to quantify with ORA and Corvist ST but are difficult to interpret and use in clinical practice due to their dependence of IOP, CCT, refractive status, time from surgery and age. Development and refinement are needed if ORA and Corvis ST should be implemented in a screening procedure of the biomechanical strength before refractive surgery.Flap‐creation technique plays a major role in changing the biomechanical stability of the cornea. Nevertheless several studies suggest that the type of procedure is not as important as the native charac‐teristics of the patient’s cornea in determining the risk for ectasia. Although we may have reached a plateau of technological improvement in excimer laser tissue ablation, the introduction of small incision lenticule extraction (ReLEx SMILE), has changed the face of corneal refractive surgery in particular in its effect on corneal biomechanics. Mathematical analysis and finite‐element models suggest that SMILE may preserve corneal biomechanical properties better than LASIK. Furthermore, the current in vivo studies performed with ORA and Corvis ST indicate that SMILE is equal or superior to LASIK in terms of preservation of the postoperative biomechanical strength.However CH and CRF were reduced after refractive surgery but no differ‐ences were found between SMILE and flap‐based (FLEx and FS‐LASIK) refractive surgeries in the RCTs. Studies have demonstrated that in LASIK and PRK, the amount of refractive error corrected is related to the changes in corneal biomechanical properties. Considerable reduction in the corneal biomechanical properties observed even in ‘flap‐less’ procedures like PRK and SMILE,Brillouin microscopy provides safe and non contact method for measuring longitudinal elastic modulus of ocular tissues. It provides three‐dimensional resolution of the imaged tissue revealing spatial variations in mechanical properties. Its clinical usefulness has already been demonstrated in corneal diagnostic and treatment monitoring and may eventually be a valuable tool for surgical planning of refractive and therapeutic procedures.question both in vivo and ex vivo, and by mathematical or finite‐element models of the cornea