Comparison Of Laser Epithelial Keratomileusis And Photorefractive Keratectomy For Myopia And Histopathological Study

Ametropia is a very common eye disease of mankind.With the rapid development of excimer laser,many kinds of surgical methods are used to correct ametropia,which includes photorefractive keratectomy(PRK),laser in-situ keratomileusis(LASIK)and laser epithelial keratomileusis(LASEK) etc. PRK has been used as the main method to treat low to moderate myopia while LASEK has been reported to be an excellent method to treat myopia in every level,especially to the high myopia.Object: We pursue the clinical investigation along with the animal of histopathological study to:1) Evaluate the effectiveness, safety, and stability of LASEK, and to compare it with conventional PRK for the purpose of choosing a better surgical method；2)To observe the morphological changes and the wound healing processes of the rabbit cornea which underwent LASEK or PRK.From these laboratory study,we hope to understand the corneal wound healing process after the excimer laser refractive surgery .Methods:1)The clinical part: In this prospective study , 70 patients with a manifest refraction of -2.25 to -9.75 diopters were treated and followed for 6 months. In each case, PRK was performed in 1 eye and LASEK in the other eye. The first eye treated and the surgical method used was randomized. Postoperative pain, epithelial healing time,manifest refraction, residual diopter and corneal haze were checked at both 3 and 6 follow up. We also use the confocal microscopy through focusing to get precise, repetitive, four-dimensional and clear images of the whole layer of cornea.2)The histopathological study part:52 New Zealand White rabbits were divided into 8 groups:normal control group(n=6),1 day, 7 days, 1, 3, 4, 5 and 6month groups(n=14).Every rabbit underwent LASEK in one eye while the other one with PRK.We use routine histological and immunohistochemical staining, Western Blot, transmission and scanning electron microscope to compare the wound healing prcess of corneal epithelium,its basement and the dynamic change of the type Ⅰ,Ⅲ,Ⅴand Ⅵ collagen in rabbit cornea of every time point.The results were analysised with image and data analysis software。Results:1)The clinical part :During the 6 month follow-up, there were no significant differences between-eyes in epithelial healing time or postoperative pain scores. For low to moderate myopia ,there were no significant differences in postoperative visual acuity 3 and 6 months comparing LASEK- and PRK-treated eyes. But for high myopia, LASEK appeared better than PRK in postoperative visual acuity and less corneal haze at 3 and 6 months time.2)The histopathological study part:①In LASEK treated rabbit eyes,the morphological study indicated that the level of corneal epithelial morphological changes,turbulent arranges of epithelium and epithelial incrassation were less than that of PRK,the time which corneal epithelial recover to normal was also significantly shorter than that of PRK.②Immunohistochemical staining and Western Blot both showed that after LASEK,the cornea wound healing with typeⅠandⅢcollagen were much faster than PRK,and the wound response was also much weaker.Whereas for type Ⅴand Ⅵcollagen,their dynamic changes were resemble between LASEK and PRK,they both reached the peak value at 3 month after the surgery,but LASEK group returned to normal earlier than PRK. The value of these two types of collagen after PRK were higher than LASEK.The changes of these four types of collagen may offer us at least partial explain to the difference of formation of corneal haze and refractive regression.③The ultrastructure changes of corneal epithelium,epithelial basement,collagen and fibroblast cell after LASEK were much less than PRK.Conclusions:1) The clinic part:① LASEK is a safe and effective method to every level of myopia,especially for high myopia.② The cornea epithelial flap may protect the wound and influece the wound healing of stroma,it may reduce the haze and stabilize the vision.③ LASEK can widen the indications of PRK.④ Confocal m...