The Experimental And Clinical Studies Of SBK

PartⅠHistopathologic and Wound Healing Characteristics of Corneas After Sub-BowmansKeratomileusisObjective To assess the proliferation of MFB and the expresion of a-SMA and TGF-β. To compare the morphologic and histopathologic changes in the rabbit cornea after SBK with PRK and LASIK Methods Twenty-seven adult New Zealand white rabbits were randomly assigned into group A, B and C. SBK was performed on the right eyes of rabbits in the group A, LASIK for group B and PRK for group C. All the left eyes were used as control. Eyeballs were enucleated and prepared for light microscopy examination in 7 days, 1m,3m after surgery. The expression ofα-SMA and TGF-βand the number of activated MFB were assessed using immunohistochemical staining. Results In the SBK group, corneal epithelium cells around the wound proliferated. The numbers of active fibroblasts were increased and thea-SMA, TGF-βwere expressed around the corneal flap and the corneal stroma. The positive expressions in SBK group are weaker than that in PRK group but stronger than that in LASIK group. Conclusion Ophthalmic pathology showed that SBK is improved in biomechanical and wound healing than conventional LASIK. However, most of the disadvantages caused by wound healing issues still remain compared to PRK.PartⅡTransmission Election Microscopy and Scanning Electron Microscopy Study of Corneal Stromal Flaps After Sub-Bowmans Keratomileusis Using MicrokeratomeObjective To observe the smoothness of corneal stromal bed, configuration of corneal flap side-cut, changes in keratocytes ultrastructure and changes in lamellar interweaving of the cornea after SBK. The visual quality and corneal biomechanics of SBK and LASIK are compared. Methods A flap was created in four eyes of normal human specimens,2 eyes for SBK group and 2 eyes for LASIK group. Six adult New Zealand white rabbits were randomly undertaken SBK microkeratome in one eye and conventional LASIK microkeratome in the other. Scanning electron microscopy was applied to observe the smoothness of corneal stromal bed and corneal flap side-cut configuration. Nine adult New Zealand white rabbits were randomly undertaken SBK microkeratome in one eye and conventional LASIK microkeratome in the other. And three rabbits without surgery were used as control. Eyeball was enucleated and prepare for transmission electron microscopy examination in 7 days,1 m, 3 m after surgery, ultrastructural changes in keratocytes and lameller were observed by TEM. Results The corneal stromal bed was more smoothy after a SBK microkeratome cut than after a conventional microkeratome cut. The corneal flap was shown to be an inverted side-cut in SBK group, while it was a standard side-cut in LASIK group. Transmission electron microscopy studies of SBK corneas showed significant changes in the direction of collagen fibrils, the degree of lamella interweaving, the activation of myofibroblasts, the crosslink of collagen and the keratocytes ultrastructure on 1 m after surgery. The changes of keratocyte ultrastructure and lamella in SBK group are prominent than that in LASIK group.Conclusion Comparing with the conventional LASIK, the more smoothy stromal bed maybe one of the reasons of better postoperative visual quality of SBK. SBK is better in maintaining corneal biomechanics than LASIK because of the strong wound healing induced by myofibroblasts and collagen lamella of the peripheral corneal flap wound.Part IIIClinical comparison study of SBK and LASIK for the treatment of high myopiaObjective To explore the efficacy and safety of SBK and LASIK for the treatment of high myopia. Methods High myopic patients more than-6.00D were treated randomly with SBK or LASIK.49 cases of 49 patients with average spherical equivalent of-7.93 D (range from-6.00 to-11.50 D) were treated with SBK, whereas 46 cases of 46 patients with average SE of-7.88 D (range from-6.00 to-10.00 D) were treated with LASIK. The uncorrected visual acuity, best corrected visual acuity, spherical equivalent, tear breakup time, corneal posterior diff were examined and recorded 1,3,6, and 12 months postoperatively. Residual stromal bed thickness and corneal flap thickness were measured during the operation. Results The mean corneal flap thickness was 108.2±11.6μm in the SBK group and 143.9±21.7μm in the LASIK group. There was significant difference in two groups. At 1,3,6,12 months postoperatively, the percentage of UCVA better than 1.0 was 95.9%,93.9%,91.8%and 91.8% in SBK group and 91.3%,93.5%,87.0% and 84.8% in LASIK group respectively. The percentage of spherical equivalent between±0.5D was 69.4%,73.5%,79.6%83.7% in SBK group and 63.0%,67.4%,69.6%,67.4% in LASIK respectively(χ2=0.428,0.422,1.263,3.428; p=0.513,0.516,0.261,0.064),showed no statistically difference. The main complications were 1 mild haze in SBK group and 2 mild refractory regression in LASIK group. BUT recover to preoperation in 3 months postoperation in SBK group while it was 6 months in LASIK group, During the operation the residual stromal bed thickness was 323.3±20.6μm in SBK group and 295.7±14.6μm in LASIK group, there was a significant statistically difference(t=7.480, p=0.038). At 12 months postoperatively, the corneal posterior diff was 0.037±0.011 m in SBK group and 0.049±0.012 mm in LASIK group, there was no significant statistically difference (t=-5.242,p=0.390). Conclusion SBK had the similar safety and efficacy with conventional LASIK. But the UCVA, SE, BUT, RSB and corneal biomechanical stability of SBK was superior to LASIK.PartⅣClinical Assessment of Visual Quality After SBK MyopiaObjective To detemine the photopic and mesopic contrast sensitivity and higher order aberrations of SBK for myopia with or without astigmatism. Methods It was a prospective randomized controlled study. Patients were divided into two groups,71cases (71 eyes) in SBK group.And 67 cases (67 eyes) in the conventional LASIK group. Only left eyes were analyzed. One year or longer after surgery, the results of the wave-front aberration, the photopic and mesopic contrast sensitivity of pre-and post-operation were recorded. The subjective visual performance after surgery was evaluated by the questionnaire. Results At 12 months post-operative, Preoperative characteristics of patients between SBK and LASIK groups was no statistical significance. One year after surgery, RMS of total HOA were 0.416±0.067μm in SBK group and 0.614±0.098μm in LASIK group(t=-13.922,p= 0.001). With regard to contrast sensitivity, SBK group achieved the preoperative levels at month 3-6 of follow up, while the LASIK groups achieved the preoperative levels at month 6-12 of follow up.When comparind the photopic and mesopic contrast sensitivity values between the two groups, the SBK group also obtained the statistically better results at low and moderate spatial frequencies. Subjective satisfication rate of SBK group was 96.2%, while 88.6% for control group. The difference was significant. Conclusion Comparing with conventional LASIK, SBK achieves a lower induceed HOA, a better and faster visual performance with contrast sensitivity test results, and a higher satisfication of patients.