The Study On Corneal Sensitivity Changes And The Interaction With Corneal Tissue After Femtosecond Laser Refractive Surgery

Purpose:To evaluate and compare the recovery of central and peripheral corneal sensitivity in the early period time after femtosecond laser assisted LASIK(FS-LASIK),small incision lenticule extraction(SMILE)and femtosecond lenticule extraction(FLEx).To observe the effect and the characteristic of photodisruption of femtosecond laser to the corneal stroma surface and the pathology and ultra-microstructure of corneal lenticule extracted from surgery of small incision lenticule extraction.To further investigate the influences of different laser pulse energy to the surface ultrastructure of corneal stroma in the flap creation with femtosecond laser,and instantaneous damage of photodisruption of femtosecond laser to human corneal tissue in vivo.Methods:1.A prospective study.81 patients(155 eyes)who underwent refractive surgery at tianjin eye hospital refractive surgery center were choice randomly.39 subjects(72 eyes)were men and 42 subjects(83 eyes)were women.There were 27 subjects(54 eyes)in FS-LASIK group,22 subjects(40 eyes)in FLEx group and 32 subjects(61 eyes)in SMILE group.Central,superior,inferior,nasal and temporal corneal sensitivity was measured using a Cochet-Bonnet esthesiometer(Luneau Ophthalmologie)before and 1weeks,1 month,3 months after surgery.The results were analyzed with Mann-Whitney test and Kruskal Wallis H test by SPSS 13.0 software.2.Contrast research.Corneal flap in 16 fresh porcine eyes were performed with 125nJ?155nJ and 195nJ pulse energy Carl Zeiss visu Max femtosecond laser and Moria-M2 microkeratome,respectively.Scanning electron microscopy was used to observe and compare the microstructure characteristic of corneal stroma bed surface after the flap created.The small incision lenticule extraction surgeries in 25 myopic eyes were performed with Carl Zeiss visu Max femtosecond laser.Light microscopy,scanning electron microscopy and transmission electron microscopy were used to observe corneal lenticule tissue extracted from surgery.Results:1.The comparison of corneal sensitivity changes between FS-LASIK and FLEx groups postoperative:There were significantly statistical differences between FS-LASIK and FLEx groups at central,superior,nasal and temporal at 1 week postoperatively(Z=-2.704,-2.899,-2.331,-2.884,P=0.007,0.004,0.020,0.004).Significantly statistical differences were obtained at every quadrant at 1 month postoperatively between FS-LASIK and FLEx groups(Z=-1.811,-1.013,-0.853,-0.643,-0.178,P=0.070,0.311,0.393,0.521,0.859).At 3 month postoperatively,there were statistical differences at central and inferior between FS-LASIK and FLEx groups(Z=-2.335,-2.608,P=0.020,0.009).2.The comparison of corneal sensitivity changes between FS-LASIK and SMILE groups postoperative:There were significantly statistical differences between FS-LASIK and SMILE groups at every quadrant at 1 week postoperatively(Z=-7.498,-4.383,-7.709,-7.881,-7.858,P<0.000).Significantly statistical differences were obtained at every quadrant at 1 month and 3 months postoperatively between FS-LASIK and SMILE groups(Z=-6.834,-4.292,-7.002,-7.598,-7.450,-7.007,-5.050,-6.256,-6.612,-5.645,P<0.000).3.The comparison of corneal sensitivity changes between FLEx and SMILE groups postoperative:There were significantly statistical differences between FLEx and SMILE groups at central,inferior,nasal and temporal at 1 week postoperatively(Z=-5.484,-7.346,-7.183,-7.657,-6.452,-7.159,-7.481,-7.729,P<0.000).Significantly statistical differences were obtained at every quadrant at 1 month postoperatively between FLEx and SMILE groups(Z=-6.452,-3.142,-7.159,-7.481,-7.729,P<0.000).There were significantly statistical differences between FLEx and SMILE groups at every quadrant at 3 months postoperatively(Z=-5.907,-2.534,-3.239,-4.509,-3.664,P=0.000,0.011,0.001,0.000,0.000).4.There were no statistical correlations between the changes of central corneal sensitivity and central corneal thickness,central corneal ablation depth,preoperative spherical equivalent(P>0.05)after FS-LASIK,FLEx and SMILE surgery(FS-LASIK group:P=0.509?0.086.0.513,FLEx group:P=0.228?0.142?0.537,SMILE group:P=0.932?0.887?0.101).5.stroma surface microstructure after flaps creation in porcine eyes:The corneal stroma was evaporated and created a smooth surface when photodisruption was happened in the simulation of flap creation with femtosecond laser.There are some remaining tissue bridges among the cavitation bubbles.The edges were regular and sharp with small damage zone and easily visible after cutting with femtosecond laser.When the energy was changed.In the 125nJ pulse energy group,there were smooth surface qualities;however,some tissue bridges were visible.While the surface showed a very smooth surface with no tissue bridges and mechanical damages in the 155 nJ pulse energy group.The surface quality was worse and showed many tissue bridges and grooves in the 195nJ pulse energy group.In addition,Ring-like slots of different size caused by big cavitation bubbles were visible this group.However,many elevated fibril tissues could be seen in the corneal surface after the flap created with microkeratome.Many crimp tissues were on the surface and the degree of irregularity was higher.It showed blunt and indentations in the cut edge.6.The ultrastructure changes of human corneal lenticule tissue under the effect of femtosecond laser:Under the light microscopy,Part of the collagen fibers in the cornea lenticule tissue with mild edema.A thin layer of tissue deep dyeing at the edge of lenticule was observed,into a linear array.The superficial of central lenticule tissue existed of a few bubbles.Under the scanning electron microscope,the anterior surface of the lenticule was relatively smooth and no obvious tissue bridge.The posterior surface of the lenticule showed slightly irregular compared with anterior surface.Scattered tissue bridge and residual traces of the effect of femtosecond laser photodisruption could be observed.Under the transmission electron microscope,adjacent collagen fiberboard layer in the corneal lenticule matrix cross each other regularly arranged.No breakage of the collagen fibers and separation of the layers.The incision of the collagen fibers on one side of the lenticule was liner alinement.It can also be observed that the central part of the lenticule was mildly damaged.However,the stroma cells near the lenticule limbus were severed damaged.Partial of the corneal stroma cells were solidified with several shivers due to the photodisruption.Some of the damaged corneal stroma cells were observed with remnants while the spaces occupied by the part of the corneal cells become fractured.Conclusion:Corneal sensitivity decreased after FS-LASIK,FLEx and SMILE surgery.The degree of corneal sensitivity decrease was evident after FS-LASIK and FLEx surgery compared with SMILE surgery.The decrease of corneal sensitivity after the SMILE was fewer and the recovery was faster compared with FS-LASIK and FLEx.This was related with no flap created during SMILE surgery and little corneal nerves was damaged.The microstructure of corneal stroma surface was smoother after the flap created with femtosecond laser compared with the flap created with microkeratome.Different surface morphological characteristic could be created by different pulse energy femtosecond laser.In the SMILE procedure,the instantaneous damage of the femtosecond laser to the corneal tissue of the focus area was mild and underwent mild thermal injury and structure change,the organizational structure of the non-focus area was to maintain a relatively complete.