The Experimental And Clinical Studies Of LASIK With Ultra-thin Corneal Flaps

Part IThe experimental study on ultra-thin comeal flapswith KM—5000D microkeratomeObjective To develop the technique of making ultra-thin corneal flaps with KM— 5000D microkeratome. Methods KM —5000D microkeratome system for ultra-thin corneal flaps was designed and manufactured. Ultra-thin corneal flaps were made by KM —5000D microkeratome on 80 fresh pig eyes, 10 human eyes in vitro and 12 rabbit eyes in vivo. The facility of the microkeratome, the size and thickness of the flaps and the rates of abnormal flaps were observed. The samples of the human corneal flaps were examined under light microscope and scanning electronic microscope. Results The automatically rotating KM—5000D microkeratome system comprised three parts: micro-cut system, double electronic dynamic device and control panel. Performing on pig eyes, human eyes and rabbit eyes, the vaccum was able to keep the intraocular pressure stable at 65mmHg. The thickness and size of flaps in pig eyes were 87.85±4.64 μm and 8.8±0.42mm, 86.4 ± 5.13 μm and 7.5±0.55mm in human eyes, 62.08 + 3.70 μm and 7.96±0.30mm in rabbit eyes. The percentage of the abnormal flaps was 18.75%, 20% and 16.67% respectively. The rates of smooth performance with the keratome were 88.75%, 80.0% and 83.33% respectively. The samples of the human corneal flaps comprised epithelium, Bowman's membrane and anterior stroma under light microscopic examination. The margin of the flap was smooth and in good order under scanning electronic microscopic examination. Conclusion It is safe, effective and predictable to make ultra-thin comeal flaps by KM—5000D microkeratome. Making ultra-thin corneal flaps for LASIK could be under clinical studies.Part IIThe effects on corneal wound healing of LASIK with ultra-thin flaps andLASEK in rabbitsObjective To evaluate the corneal wound-healing response of LASIK with ultra-thin corneal flaps and LASEK in rabbits. Methods 32 adult New Zealand rabbitswere divided into 2 groups with 16 each. Two surgical procedures, LASIK with ultra-thin flaps and LASEK were performed on the right eye of each group, with the left eye as control. A myopic ablation of 10 diopters was performed in each group. Corneal wound-healing and histopathological changes of the ablation zone were studied through slit lamp, light microscope and transmission electronic microscope. The expression levels of collagen I, collagen III, fibronectin (FN) and transforming growth factor beta-1 (TGF-& 1) were investigated by immunohistochemistry and RT-PCR assays. Results In the group of LASIK with ultra-thin flaps, the corneas were clear without haze followed by slight wound healing and fast recovery. While in the group of LASEK, corneal wound healing was obviously delayed. There was haze in grade 1 (62.5%) and grade 2 (37.5%) in 1 month, with grade 0.5 (43.75%) and grade 1 (56.25%) in 3 months. 1 month and 3 months after surgery, proteins and mRNA of collagen III, FN and TGF- P 1 were expressed in the anterior corneal stromal layer in each group. But the expression was much higher in the group of LASEK (PO.05). The protein and mRNA expression of collagen I had no difference between the two groups (P>0.05). The mRNA expression of collagen I, collagen III, FN and TGF- 3 1 had no statistical difference between the groups of control and LASIK with ultra-thin flap in 3 months (P>0.05). Conclusion According to the animal experiments, it was suggested that the corneal wound-healing response of LASIK with ultra-thin flaps was much better than of LASEK.Part fflThe clinical study on LASIK with ultra-thin flaps and LASEK for extremelyhigh myopiaObjective To investigate the effects of KM—5000D microkeratome for LASIK with ultra-thin flaps and to evaluate the clinical efficacy, safety and predictability of LASIK with ultra-thin flaps for extremely high myopia. Methods 42 eyes of 26 cases with a spherical equivalent over -10 diopters were divided into two groups. 21 eyes of 14 cases received LASIK with ultra-thin flaps were included in group A. 21 eyes of 12 cases received LASEK were included in group B. The mean preoperative spherical equivalent was -14.23+ 2.28D and -12.85+ 2.28D respectively. Clinical efficacy and complications were observed and compared during and after surgery. Results The ultra-thin flap making by KM —5000D microkeratome was smooth and safe. There were no threatening complications for vision during surgery. The average flap thickness was 88.81 +2.75um. Postoperative visual acuity of group A recovered faster with less steroid use than of group...