Effect of amniotic membrane transplantation on rabbit conjunctival surface reconstruction at the recovering stage of alkali burn

AIM: (1) To investigate the effect of amniotic membrane transplantation (AMT) on rabbit conjunctival surface reconstruction with severe alkali burns. (2) To evaluate the possibility of AMT treatment for ocular alkali burns during recovering stage. METHODS: Animal models were established on 30 eyes of rabbits by creating severe alkali burns on the conjunctiva from the upper corneal limbus to the upper conjunctival fornix. Preserved human amniotic membrane transplantations and reconstruction of conjunctival fornix were performed at one week after injury (recovering stage). Epithelium growth of burned area after transplantation was observed using light microscope at 1, 2, 3, 4, and 8 weeks. Conjunctival tissue in transplantation area was collected at 1, 4 and 8 weeks. The ultrastructure of the collected tissue was studied by electron microscope. The results were compared with control group, which received only vitamin C subconjunctival injection and antibiotic eye drops as treatment for alkali burn. Exterior eye pictures were also taken at the end of the observation, the width from upper corneal limbus to the edge of upper fornix was measured. Data were analyzed statistically. RESULTS: (1) In the transplant group, conjunctival epithelium growth was observed in the area of AMT under both light and electron microscope 1 week after surgery. At the 4(th) week, conjunctival epithelium with goblet cells that resembled normal conjunctival tissues was observed in the whole amniotic membrane area. At the 12(th) week, the conjunctival epithelium on the amniotic membrane was well formed, and the connective tissue under the epithelium was loose at the fornix. No fibrosis was identified. In contrast, conjunctival epithelium necrosis was observed in the control group at 2 weeks after alkali burns. Reepithelization did not occur through the 12-week observation. Severe fibrosis with inflammatory cells infiltration was observed between 4 to 8 weeks. At the 12(th) week, fibrosis of the connective tissue at the fornix developed and there were no conjunctival epithelium covering the burned area. (2) In the transplant group, the conjunctiva in transplanted area had no scarring and appeared smooth at the 12(th) week. Upper fornix was reconstructed. The depth of fornix was 7.9 +/- 0.3mm (7.6-8.2mm), which was approximate to the normal depth 8.2 +/- 0.2mm (8.0-8.4mm, P>0.05). While in the control group, the burned area appeared rough with granuloma formation and severe scarring. Upper fornix became shallow. The depth of fornix was 3.1 +/- 1.7mm (1.0-4.5mm.), and significant difference was found between control and transplant group (P<0.01). CONCLUSION: Human amniotic membrane preserved in glycerin can promote cell adhering, migrating and differentiating of normal conjunctival epithelium. Reconstruction of conjunctival surface in early stage of alkali burn can be achieved by AMT. AMT can effectively prevent symblepharon formation.