| [Objective]To explore the changes of corneal morphology,corneal densitometry,high-order aberrations and corneal epithelial remodeling after laser-assisted in Situ Keratomileusis(LASIK)combined with prophylactic corneal collagen cross-linking(CXL)(LASIK Xtra)for myopia correction.[Methods]This study prospectively included myopic patients who underwent LASIK and LASIK Xtra surgeries at the Refractive Surgery Center from October 2021 to July 2022.All patients underwent visual acuity,intraocular pressure,optometry,slit lamp anterior segment and fundus examination,Pentacam examination,and Anterior-segment optical coherence tomography(AS-OCT)before and 3 months after surgery.1.Corneal morphology research.This study enrolled 23 individuals(46 eyes)in the LASIK group and 23 individuals(46 eyes)in the LASIK Xtra group,respectively.Pentacam was used to measure and record the corneal morphological parameters and thickness parameters of all patients before and after surgery.And the corneal morphological changes after surgery were compared between the two groups.2.Corneal densitometry research.This study enrolled 23 individuals(46 eyes)in the LASIK group and 23 individuals(46 eyes)in the LASIK Xtra group,respectively.The corneal densitometry values of different layers and diameters of the cornea were measured using Pentacam’s densitometry analysis software.The changes in corneal densitometry after surgery were compared between the two groups.3.Corneal high-order aberrations research.This study enrolled 23 individuals(46 eyes)in the LASIK group and 23 individuals(46 eyes)in the LASIK Xtra group,respectively.Using Pentacam’s aberration analysis software,known as "Zernike analysis",to compare the changes in corneal higher-order aberrations between two groups after surgery.4.Corneal epithelial remodeling research.This study enrolled 25 individuals(50 eyes)in the LASIK group and 25 individuals(50 eyes)in the LASIK Xtra group,respectively.Using AS-OCT(RTVue XR)to measure the corneal epithelial thickness topographic map with a diameter of 6mm.The changes in corneal epithelial thickness after surgery were compared between the two groups.[Results]1.At 3 months after surgery,the UDVA(LogMAR)of the LASIK group and the LASIK Xtra group were 0.01 ± 0.07 and 0.04± 0.12,respectively(P=0.203).The postoperative spherical equivalent of the two groups were-0.13 ± 0.96 D and-0.40 ±1.09 D,respectively(P=0.244).2.At 3 months after surgery,for the anterior surface of the cornea,the FELE,K1,K2,Astig,and Ecc values of the two groups were significantly lower than before surgery,while the Q values were significantly higher than before surgery,with statistically significant differences(all P<0.001).However,there was no significant difference in the changes in various anterior surface parameters before and after surgery between the two groups(all P>0.05).For the posterior surface of the cornea,in the LASIK group,postoperative BELE and Ecc values were significantly lower than before surgery,while K1,K2,and Q values were significantly higher than before surgery,with statistically significant differences(all P<0.05).In the LASIK Xtra group,only BELE significantly decreased after surgery(P<0.001).The changes in △K1,△Ecc,and △Q values in the LASIK group before and after surgery were more significant than those in the LASIK Xtra group(all P<0.05).For the topographic index,the ISV,IVA,IHA,and IHD of the two groups significantly increased compared to before surgery,while KI and CKI significantly decreased compared to before surgery,with statistically significant differences(all P<0.05).Before and after surgery,the △KI of the LASIK group decreased more significantly than that of the LASIK Xtra group(P=0.007),while the△IHA of the LASIK Xtra group increased more significantly than that of the LASIK group(P=0.022).3.From the specific comparison of various levels and diameter ranges,the postoperative corneal densitometry values of the LASIK group decreased significantly in the range of 6-10mm diameter in the anterior layer,0-10mm diameter in the middle layer,and 0-2mm diameter in the posterior layer(all P<0.001).The postoperative densitometry values of the LASIK Xtra group increased significantly in the range of 0-6mm diameter in the anterior layer and 6-10mm diameter in the posterior layer,while slightly decreased in the range of 0-2mm diameter in the middle layer(all P<0.05).Compared with the LASIK group,the LASIK Xtra group showed more changes in densitometry values within the range of 0-10mm diameter in the anterior layer,0-10mm diameter in the middle layer,and 6-10mm diameter in the posterior layer(all P<0.05).4.At 3 months after surgery,both groups showed a significant increase in RMS-HOA values on the anterior and posterior surfaces of the cornea,as well as the whole cornea,with statistically significant differences(all P<0.001).However,there was no significant difference in the changes in total higher-order corneal aberrations between the two groups at all levels before and after surgery(all,P>0.05).The specific aberrations at all levels of the cornea in the LASIK group did not show significant changes compared to before surgery(all P>0.05).In the LASIK Xtra group,the trend of changes in various aberrations on the anterior surface of the cornea was consistent with that of the whole cornea,showing a significant increase in postoperative Z40,Z31,Z3-1(negative),and Z3-3 compared to before surgery(all P<0.05).The posterior surface of the cornea showed a significant increase in postoperative Z40(negative),Z31(negative),and Z3-1(all P<0.05).The changes in spherical aberration,coma,and oblique trefoil on the anterior surface and whole cornea of the LASIK Xtra group before and after surgery were significantly greater than those in the LASIK group(all P<0.05),and the changes in vertical coma on the posterior surface of the cornea were also significantly greater than those in the LASIK group(P=0.004).5.At 3 months after surgery,both groups showed significant thickening of the average corneal epithelium in the central 2mm zone and 2-5mm diameter zone compared to before surgery(all P<0.001),with the most significant thickening in the paracentral inferotemporal section,and the average corneal epithelium in the 5-6mm zone significantly thinning compared to before surgery(all P<0.05).There was no significant difference in the changes of corneal epithelial thickness of all sections and topographical thickness variability between groups within a diameter range of 6mm(all P>0.05).[Conclusion:]1.In terms of vision and refractive outcome:in the early postoperative period,LASIK Xtra is safe and effective in correcting myopia,and its effect is comparable to LASIK.2.In terms of corneal morphology:In the early postoperative stage,the changes in corneal anterior surface morphology of LASIK Xtra are similar to LASIK,while the changes in posterior surface morphology are more stable than LASIK.Although there was a more significant increase in corneal asymmetry after LASIK Xtra compared to LASIK,no morphological manifestation of keratectacia was observed in the early postoperative stages of both procedures.3.In terms of corneal densitometry:In the early postoperative stage,the corneal densitometry value of LASIK decreases compared to before surgery.The change in densitometry values before and after LASIK Xtra surgery is less or even greater than that of LASIK,with the difference mainly concentrated in the 0-10mm full diameter range of the anterior and middle layers,which is also the surgical area and CXL action area.Although LASIK Xtra can increase corneal densitometry and reduce corneal transparency compared to LASIK,it does not affect postoperative visual acuity or increase complications such as corneal haze and diffuse lamellar keratitis.4.In terms of corneal higher-order aberrations:In the early postoperative period,compared with LASIK,LASIK Xtra does not increase the total higher-order aberrations at all levels of the anterior and posterior surfaces of the cornea,as well as the whole cornea.In addition,the specific aberrations of the anterior surface and whole cornea of LASIK Xtra are consistent,manifested as significant increases in spherical aberration,horizontal coma,vertical coma(negative),and oblique trefoil.The posterior surface has a certain aberration compensation effect on the anterior surface.The increase in spherical aberration,coma,and trefoil after LASIK Xtra surgery may be related to the changes in corneal morphology regularity and biomechanical properties caused by combined prophylactic CXL.5.In terms of corneal epithelial remodeling:In the early postoperative stage,the characteristics of corneal epithelial remodeling response after LASIK Xtra surgery are similar to LASIK,with significant thickening of the central and paracentral corneal epithelium compared to before surgery.Among them,the thickening is most obvious in the paracentral inferotemporal section,and the mid-peripheral zone is significantly thinner than before surgery.Compared with LASIK,LASIK Xtra does not additionally induce corneal epithelial hyperplasia. |
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