Unintended changes in ocular biometric parameters during a 6-month follow-up period after FS-LASIK and SMILE

Background:Corneal refractive surgery has become reliable for correcting refractive errors,but it can induce unintended ocular changes that alter refractive outcomes.This study is to evaluate the unintended changes in ocular biometric parameters over a 6-month follow-up period after femtosecond laser-assisted laser in situ keratomileusis(FS-LASIK)and small incision lenticule extraction(SMILE).Methods:156 consecutive myopic patients scheduled for FS-LASIK and SMILE were included in this study.Central corneal thickness(CCT),mean curvature of the corneal posterior surface(K_(pm)),internal anterior chamber depth(IACD)and the length from corneal endothelium to retina(ER)were evaluated before and after surgery over a 6-month period.Results:Both the FS-LASIK and SMILE groups(closely matched at the pre-surgery stage)experienced flatter Kpm,shallower IACD and decreased ER 1 week post-surgery(P<0.01),and these changes were larger in FS-LASIK than in SMILE group.During the 1 week to 6 months follow up period,K_(pm),IACD and ER remained stable unlike CCT which increased significantly(P<0.05),more in the FS-LASIK group.Conclusions:During the follow up,the posterior corneal surface became flatter and shifted posteriorly,the anterior chamber depth and the length from the corneal endothelium to retina decreased significantly compared with the pre-surgery stage.These unintended changes in ocular biometric parameters were greater in patients undergoing FS-LASIK than SMILE.The changes present clear challenges for IOL power calculations and should be considered to avoid affecting the outcome of cataract surgery.

Biomechanical diagnostics of the cornea

Corneal biomechanics has been a hot topic for research in contemporary ophthalmology due to its prospective applications in diagnosis,management,and treatment of several clinical conditions,including glaucoma,elective keratorefractive surgery,and different corneal diseases.The clinical biomechanical investigation has become of great importance in the setting of refractive surgery to identify patients at higher risk of developing iatrogenic ectasia after laser vision correction.This review discusses the latest developments in the detection of corneal ectatic diseases.These developments should be considered in conjunction with multimodal corneal and refractive imaging,including Placido-disk based corneal topography,Scheimpflug corneal tomography,anterior segment tomography,spectral-domain optical coherence tomography(SD-OCT),very-high-frequency ultrasound(VHF-US),ocular biometry,and ocular wavefront measurements.The ocular response analyzer(ORA)and the Corvis ST are non-contact tonometry systems that provide a clinical corneal biomechanical assessment.More recently,Brillouin optical microscopy has been demonstrated to provide in vivo biomechanical measurements.The integration of tomographic and biomechanical data into artificial intelligence techniques has demonstrated the ability to increase the accuracy to detect ectatic disease and characterize the inherent susceptibility for biomechanical failure and ectasia progression,which is a severe complication after laser vision correction.