The Design Of One-piece Nonpenetrating Keratoprothesis And Animal Experiments

Objective: To establish rabbit dry eye model, and evaluate validity and stability of the method. The aim of the study is to evaluate biological response of rabbit cornea to microporous Poly(2-hydroxyethyl methacrylate) (PHEMA) and porous Polymethyl methacrylate(PMMA). Then we developed new types of one-piece nonpenetrating PHEMA and PMMA keratoprothesis (Kpro) (the latter including KproⅠand KproⅡ). To evaluate application value of the newly-designed Kpro, we implanted it to corneas of dry eye rabbits and observed clinical responses, then discussed the design, the surgery techniques and postoperative, complications.Materials and methods: (1)Surgery was performed on 14 New Zealand rabbits' right eyes by removing the lacrimal gland, the tertiary eyelid and the Harder's gland and burning the fornical conjunctiva with 50% trichloride acetic acid. ShirmerⅠtest and rose Bengal staining were taken on day 1, 3, 5, 7, 10 and 15 after surgery. We compared the condition of the right eye before and after surgery. Enucleation was performed 3 weeks after surgery and the excised cornea and conjunctiva were observed by light microscopy, transmission and scanning microscopy for examining the morphologic change of the superficial epithelial cells. Meanwhile the right eye was compared with the left one. (2) 12 dry eye rabbit were individed into two groups on random. Disc of microporous PHEMA or porous PMMA was implanted into the right cornea separately. Rabbits were sacrificed 0.5, 1, 2 months after surgery, for examining the excised cornea by light microscopy and transmission microscopy. (3) It was successful to develop PHEMA Kpro by polymerizing and agglutinating with PHEMA particulates and it was also successful to develop PMMA Kpro by cutting and polishing. Our Kpro includes anterior, posterior piece and central optic, and the figure was similar to the one of "工". (4) Surgery techniques: firstly make corneal pocket, secondly trephine the anterior central corneal lamella, thirdly buried the posterior piece into the lamellar pocket, fix the central optic through the hole of trephination and fix the anterior piece to the surface of anterior corneal lamella. It is no need to fix the Kpro with suture. (5) PHEMA Kpro was implanted to three dry eye rabbits, numbering NO.1, NO.2, NO.3, and then clinical outcomes were observed. (6) PMMAⅠKpro was implanted to NO.1, NO.2 and NO.3 dry eye rabbits and PMMAⅡKpro was implanted to NO.4 and NO.5 rabbits. Then we observed the clinical outcomes.Results: The values of SchirmerⅠtest before surgery was 18.1±3.6mm, but the values of SchirmerⅠtest after surgery decreased gradually and stably and all of the values were below 5mm five days after surgery. The values of SchirmerⅠtest showed significant difference before and after surgery. Before operation the result of 1% rose Bengal staining was negative, but it became positive on 7 days after surgery and the extent of staining was aggravated along with time. The examination of cornea and conjunctiva by light, transmission and scanning eletron microscopy revealed abnormal. (2) Within one week after surgery, the symptoms of the right eye were ameliorated evidently. By two weeks after implantation, corneal fibroblast cells and deposition of collagens were found in the pores of PHEMA and PMMA material, migrating forward to the center of materials gradually. (3) Surgery techniques are feasible: the posterior piece was buried into lamella pocket, central optic was fixed through the hole of trephination and anterior piece was fixed to the surface of the anterior cornea lamella. (4) PHEMA Kpro group. NO.1 and NO.2: the anterior piece turned up and region between central optic and posterior piece dehisced on the first day after surgery. Kpro had been retained for only one day and displaced and extruded at last. NO.3: the similar instance occurred and the Kpro had been retained for six days after surgery. (5) PMMA Kpro group. Corneal staphyloma and leakage of aquous humor occurred to NO.4 rabbit on three days after surgery because of trephine through the posterior corneal lamella during operation. The thing was aggravated on seven days after surgery and so we ended observation of NO.4 rabbit. The rest of PMMA Kpro have been retained during the experiment without severe complications such as corneal melting, aqueous humor leakage and extrusion. So far, the Kpro of NO.1 has been retained for more than four months. During experiment the posterior corneal lamella keep transparence basically except for NO.2 rabbit.Conclusion: (1) It is successful to establish dry eye rabbit model by removing the lacrimal gland, the tertiary eyelid, the Harder's gland and burning the fornical conjunctiva with 50% trichloride acetic acid.(2) Even under dry eye condition, PHEMA and PMMA have favorable biological compatibility, permitting corneal fibroblast cells ingrowthing and collagens depositing into the porous.(3) It is successful to develop PHEMA Kpro by polymerizing and agglutinating with PHEMA particulates.(4) It is also successful to develop PMMA Kpro by cutting and polishing.(5) Surgical techniques are feasible: the posterior piece is buried into lamella pocket, central optic is fixed through the hole of trephination and anterior piece is fixed to the surface of the anterior cornea lamella.(6) To reestablish the vision of dry eye rabbit model, PHEMA maybe not the suitable material.(7) The PMMA Kpro can be retained to the cornea of the dry eye rabbit stably without severe complications, at least in short time.(8) The design of PMMAⅡKpro may be more reasonable than the one of PMMAⅡKpro, because the former can ameliorate the nutrition metabolizability, but there is no enough evident between the clinical outcomes of two types...