The Experimental And Clinical Studies Of Epi-Lasik With On-Flap And Off-Flap On Myopia Correction

There has been more and more interest in epipolis laser in situ keratomileusis(Epi-LASIK) for its many advantages such as applying to the patients whose cornea was thin, corneal curvature was comparatively large, eye easy was traumatic.As one of surface ablation modalities, Epi-LASIK was expanding the range of excimer laser in therapying ametropia. At the same time, in this operation corneal irritation symptoms and corneal haze were lessened apparently than in photorefractive keratectomy(PRK)and laser subepithelial keratomileusis(LASEK). Some complications related with laser in situ keratomileusis(LASIK) such as free flap,broken flap, corneal epithelium implantation, iatrogenic cornea extention,et al could be avoided in this operation, so it is safety and effectivity in Epi-LASIK therapying myopia. In On-flap Epi-LASIK, corneal epithelium flap was repositioned after laser remotioning corneal stroma, however, some doctors of in and outside the country discarded the corneal flap on purpose which called Off-flap Epi-LASIK. There were no final conclusions at international if there were differences and what differences of On-flap Epi-LASIK and Off-flap Epi-LASIK. In our study, animal experiment and clinical research were done to contrast this two modus operandi. Through setting up the animal models of on-flap Epi-LASIK and off-flap Epi-LASIK in histopathology and molecular biology to study the effects of different way of corneal epithelium wound healing and making prospective studies for this two operation, different clinical effectiveness was made to provide the basis for the selection of a suitable surface ablation modality in photorefractive corrections.Part I To study the different way of corneal epithelium wound healing and the early inflammatory response of cornea on On-flap Epi-LASIK compared to Off-flap Epi-LASIK in rabbitsObjective:To evaluate the effect of different way of corneal epithelial wound healing and the early inflammatory response of cornea on On-flap Epi-LASIK compared to Off-flap Epi-LASIK in rabbits.Methods:34healthy Albino white rabbits(68eyes)were used as experimental animals and32of them were randomly divided into4groups (1d,3d,5d,7d) with one eye for On-flap Epi-LASIK and the other eye for Off-flap Epi-LASIK and2of them without treatment were served as blank controls.The way of the corneal epithelium wound healing was observed at1,3,5,7days after surgery by light micrograph and transmission electron microphotograph after On-flap Epi-LASIK and Off-flap Epi-LASIK. The immunohistochemical technique was used to detect the number of the apoptotic cells in the corneal stroma and the expressions of both Basic fibroblast growth factor(bFGF) and proliferin Ki-67in the corneal stroma.Results:1. Different feature of the epithelial healing:Light micrograph and transmission electron microscopy demonstrated that at the first day after surgery the epithelial flap was getting a little thinner and the basement membrane of the corneal epithelium in On-flap Epi-LASIK specimens conjuncted with stroma tightly, the microvilli on the epithelial surface reduced, a small number of the basal cells showed edema. The above indicated that the cell viability of epithelial flap was still better in a proper way. At the third day after surgery, the edema of the epithelium flap in the On-flap Epi-LASIK specimens reached to peak. The perinuclear space was expanded and there was the edema of the chondriosome too. At the fifth day after the surgery,the edema of epithelium in the On-flap Epi-LASIK specimens resolved gradually and the microvilli on the epithelial increased than before. At the seventh day after surgery, some epithelial cells of outer layer necrosised and ablated gradually. At the first day after surgery, there was one layer of neogenesis corneal epithelium cell covered the filed of operation in Off-flap Epi-LASIK specimens. At the3to5days after the surgery, the new corneal epithelium increased layer by layer to4-5epithelial cell layers and the microvilli on the epithelial surface increased without obvious edema of epithelium. At the seventh day after the surgery the epithelium cells were5-6sheets and the epithelium cell accreted with the stroma well. The epithelium cell basilar membrane were both integrity. The alignment of the fiber in the corneal stroma is regularity.2. Keratocyte apoptosis:At the first day after surgery, no difference in TUNEL positive cells were seen between specimens of On-flap Epi-LASIK and Off-flap Epi-LASIK(P>0.05);There was a significant difference for the more number keratocyte apoptosis in On-flap Epi-LASIK compared to Off-flap Epi-LASIK specimens at3,5days after surgery (p<0.05); At the seventh day after surgery, there was no TUNEL positive cells both in On-flap Epi-LASIK and Off-flap Epi-LASIK.3. Expression of bFGF in the cornea:There was no statistically significant difference in the expression of bFGF in the corneal stroma between On-flap Epi-LASIK and Off-flap Epi-LASIK specimens at1,7days after surgery (P>0.05).But there was a significant increase in the expression of bFGF in the corneal stroma of Off-flap Epi-LASIK compared to On-flap Epi-LASIK specimens at3,5days after surgery (p<0.05). 4.Expression of Ki-67in the cornea:There was no statistically significant difference in the expression of Ki-67in the corneal stroma between On-flap Epi-LASIK and Off-flap Epi-LASIK specimens at7days after surgery (P>0.05). But there was a significant increase in the expression of Ki-67in the corneal stroma of On-flap Epi-LASIK compared to Off-flap Epi-LASIK specimens atl,3,5days after surgery (p<0.05).Conclusions:There were the specific way of both the epithelium removal and epithelium healing in Off-flap Epi-LASIK comparing to On-flap Epi-LASIK.Therefore, Off-flap Epi-LASIK possibly has a potential advantage over On-flap Epi-LASIK in reducing inflammatory response and irritation symptoms in prophase and the forward incidence of corneal Haze after surface ablation laser refractive surgery.PartⅡ Clinical study of removing or reserving the epithelial flap on myopia correction by Epi-LASIKObjective:To compare the advantages and disadvantages on low-to-moderate myopia and high myopia of removing or reserving epithelial flap during epipolis laser in situ keratomileusis (Epi-LASIK) and to offer references in selecting refraction surgery styles.Methods:A prospectively, double-masked and randomized study was performed on192eyes of96patients including112eyes of low-to-moderate myopia(A group) and80eyes of high myopia(B group). When getting the agreement of each patient, one eye underwent On-flap Epi-LASIK (A1,B1group) randomly and the other eye had Off-flap Epi-LASIK(A2,B2group). All eyes wore bandage contact lens after operation. Corneal irritation symptoms and time of corneal healing were observed after operation;Visual acuity, refractive and corneal haze were evaluated within6months postoperatively. The data was statistical analysis by paired t-test.Results:1. Pain:On post operative day1, the difference of subjective mean pain of group Al and group A2with group B1and group B2were not statistically significant (P>0.05);On post operative day2,3and5, the difference of group Al and group A2with group B1and group B2were statistically significant (P<0.05).2. Corneal irritation symptoms:On post operative day1, the difference of corneal irritation symptoms of group A1and group A2with group B1and group B2were not statistically significant(P>0.05);On post operative day2,3and5, the difference of group Al and group A2with group B1and group B2were statistically significant (P<0.05).3. Corneal epithelial healing time:The mean time of epithelial healing in groupAl and groupA2was4.56±1.12days and3.02±0.63days respectively, there was significant difference between two groups (P <0.05); The mean time of epithelial healing in groupBl and groupB2was4.92±1.38days and2.96±0.51days respectively, there was significant difference between two groups (P<0.05)4. The uncorrected visual acuity (UCVA):The mean UCVA on post operative day7of groupAl was lower than groupA2and the difference was statistically significant (P<0.05); The mean UCVA on post operative day7of groupBl was lower than groupB2and the difference was statistically significant (P<0.05);The difference of UCVA of groupAl and groupA2at1st,6th month was not statistically significant (P>0.05); The difference of UCVA of groupB1and groupB2at1st,6th month was not statistically significant (P>0.05)5. The mean spherical degree and the mean cylindrical degree:The difference of mean spherical degree of groupAl and groupA2with groupBl and groupB2at1st,6th month postoperatively was not statistically significant (P>0.05);The difference of mean cylindrical degree of groupAl and groupA2with groupBl and groupB2at1st month postoperatively was statistically significant (P<0.05);The difference of mean cylindrical degree of groupAl and groupA2with groupBl and groupB2at6th month postoperatively was not statistically significant (P>0.05)6. Haze:On the developing of corneal haze after the operation, there were not statistical difference between groupAl and groupA2at the1st and6th month respectively (P>0.05), but there were statistical difference between groupBl and groupB2at the1st and6th month respectively (P<0.05).Conclusions:1.To both low-to-moderate myopia and high myopia,the Off-flap Epi-LASIK seem to reduce pain and other uncomfortable symptoms in early postopertative period and shorten the epithelial healing time and increase the cornea transparence with better UCVA.2. To both low-to-moderate myopia and high myopia, the uncorrected visual acuity improved gradually at1st,6th month postoperatively whether removing or reserving the epithelial flap.3. There were difference between low-to-moderate myopia and high myopia of corneal haze at1st,6th month postoperatively in On-flap Epi-LASIK and Off-flap Epi-LASIK. To low-to-moderate myopia, there was no difference of corneal haze at1st,6th month postoperatively in On-flap Epi-LASIK and Off-flap Epi-LASIK.But to high myopia,the corneal haze of On-flap Epi-LASIK was obviously slighter than that of Off-flap Epi-LASIK.