EyeWorld India June 2013 Issue

52 EWAP CORNEA June 2013 extremely useful tool for the ocular surface surgeon, but it is not a magic wand,” said Darren G. Gregory, MD , associate professor, University of Colorado Hospital and Eye Center, Aurora, Colo., USA. Surgeons must be aware of both its benefits and limitations. If the ocular surface “is very disordered, amniotic membrane is not going to fix everything,” and surgeons still need to address other surface issues, whether with punctal plugs or mucous membrane grafts (to provide the lid with a more normal architecture). If the patient presents with a more superficial problem, using the membrane as a biological corneal bandage (ProKera) would likely be successful, Dr. Tseng said. “But if there’s tissue loss of any significance, using cryopreserved amniotic membrane (AmnioGraft) as a surgical graft in the affected area allows surgeons to put whole cells into the defect,” he said. Although both AmnioGraft and ProKera are cryopreserved membranes, the applications are different, said Esen K. Akpek, MD , associate professor of ophthalmology, and director, Ocular Surface Diseases and Dry Eye Clinic, Wilmer Eye Institute, Johns Hopkins University, Baltimore, Md., USA. When the defect involves both the conjunctiva and cornea, she uses ProKera. “It helps avoid shrinkage of the conjunctiva after the acute onset of the trauma, whatever that trauma may be—infection or inflammation, alkali burns or thermal burns,” she said. Conversely, in cases of non-healing epithelial defects, infectious keratitis or ulcers, where the infection has resolved but healing issues remain, “I like to use the cryopreserved membrane without the ring (AmnioGraft).” A significant amount of tissue loss in the corneal stroma necessitates “some substance to plug a frank perforation, and in those cases I like to use the heat- dried version (Ambio5) because it’s about 110 µm thick, so there’s a lot of substance to it.” Views from Asia-Pacific Hungwon TCHAH, MD Professor, University of Ulsan, Asan Medical Center 388-1 Pungnab-dong Songpa-gu, Seoul, Korea Tel. no. +82-2-30103680 Fax no. +822-2-4706440 hwtchah@amc.seoul.kr T he amnion comprises the three innermost layers of the placenta: a single epithelial layer, a thick basement membrane, and an avascular stroma. The basement membrane serves as biological scaffold, and the stroma sequesters a wide range of growth factors, such as EGF, TGF-a,-b1, -b2 and -b3, KGF, HGF, bFGF, VEGF, and PDGF. Thus, amniotic membrane has been widely used for various ocular surface disorders as a patch in corneal surface reconstruction, a graft in corneal and conjunctival surface reconstruction, and an adjunct to limbal transplants. The fresh, non-preserved amniotic membrane is certainly rich in growth factors, but residual cellular components of the donor may induce an immune reaction after amniotic membrane implantation. In addition, it is not easily available at the time of operation. Thus, preserved forms of amniotic membrane are commonly used. There are two representative forms of amniotic membrane available according to the preparation method: 1) cryopreserved form and 2) dried form, either freeze- (lyophilized) or heat-dried. The biological constituents, including growth factors and the structure of the cryopreserved amniotic membrane, closely resemble fresh, non-preserved amniotic membrane. Because this cryopreserved amniotic membrane is thicker than the dried forms and has more tensile strength, it would be more appropriate for deep tissue defects and bandage purposes. Freeze- or heat-dried forms of amniotic membrane macroscopically appear more fragile than the cryopreserved material. Lyophilization may cause protein denaturation and changes in tissue structure. A diminishing level of growth factor TGF-a, -b1, -b2 and -b3, VEGF, PDGF-A and -B, KGF, bFGF, EGFR and TGF-b2 receptors is reported in lyophilized denuded AM treated with γ -irradiation compared with cryopreserved amniotic membrane. 1,2 However, dried forms of amniotic membrane are thinner and more transparent due to the removal of water; this could make vision better than with thicker, cryopreserved amniotic membranes. In addition to the three categories in which amniotic membrane makes the most sense according to Kimberly C. Sippel, MD, another option for treatment may be considered. A multilayered amniotic membrane transplantation can be performed in cases of associated corneal thinning or corneal melts. Rodriguez-Ares et al. reported that multilayered amniotic membrane transplantation was effective for treating corneal perforations with diameters less than 1.5 mm, 3 while Kim et al. reported on the effectiveness of fibrin glue-assisted augmented amniotic membrane transplantation in corneal perforations more than 2 mm in greatest dimension. 4 Recently, the method of pulverizing the amniotic membrane and applying it to eyes with surface disorders has been introduced and has shown hopeful results. In conclusion, amniotic membrane use in ophthalmic surgery is expected to provide an alternative for corneal and conjunctival reconstruction in many clinically challenging situations in the future. Reference 1. Mehta JS, Riau A, Tan DT, Beuerman RW. Analysis of matrix proteins, growth factors and membrane surface in commercial available freeze-dried amniotic membrane. Proceedings of ARVO 2008 Annual Meeting; 2008 April 27–May 1; Fort Lauderdale, USA. Invest Ophthalmol Vis Sci . 2008;49:E-Abstract 5745. 2. Bhatia M, Pereira M, Rana H, et al. The mechanism of cell interaction and response on decellularized human amniotic membrane: implications in wound healing. Wounds . 2007;19:207–17. 3. Rodriguez-Ares MT, Touriño R, Lopez-Valladares MJ, et al. Multilayer amniotic membrane transplantation in the treatment of corneal perforations. Cornea. 2004;23:577-83. 4. Kim HK, Park HS. Fibrin glue--assisted augmented amniotic membrane transplantation for the treatment of large noninfectious corneal perforations. Cornea. 2009;28:170-6. Editors’ note: Prof. Tchah has no financial interests related to his comments Amniotic - from page 50