Amniotic Membrane Transplant
Amniotic membrane is the innermost layer of the placenta consisting of a thick basement membrane and an avascular stromal matrix. It can been used as a graft and as a dressing to facilitate ocular surface reconstruction and to promote healing.
Amniotic membrane, or amnion, is the innermost layer of the placenta and consists of a thick basement membrane and an avascular stromal matrix. Amniotic membrane transplantation has been used as a graft or as a dressing in different surgical subspecialties. In the field of ophthalmology, this tissue has been used as a tissue bandage for cornea infections and sterile melts, and to reconstruct the ocular surface for various procedures.
Live fetal membrane which included both amnion and chorion was first documented by De Rotth in 1940 for use in conjunctiva reconstruction. A very low success rate was reported. During the same year, Brown used rabbit peritoneum as a temporary patch for ocular surface burns which Sorsby later modified with human amniotic membrane in 1946 and 1947. In 1995 Kim and Tseng reintroduced the idea of amniotic membrane for ophthalmic use which has since become increasing more popular.
Mechanism of Action
The basement membrane component of amniotic membrane is similar in composition to the conjunctiva. For this reason, current theory suggests that amniotic membrane augments support for limbal stem cells and cornea transient amplifying cells. Clonogenicity is maintained which promotes both goblet and non-goblet cell differentiation while excluding inflammatory cells and their protease activities.  Furthermore, it suppresses myofibroblast differentiation of normal fibroblasts to reduce scar and vascular formation. This action assists healing for conjunctiva reconstruction, epithelial defects, and stromal ulceration.
After surgical removal of the pterygium a conjunctiva defect remains. This defect could be left alone to heal by secondary intention, sutured directly via primary closure, grafted with a conjunctiva autograft, or grafted with amniotic membrane. With intraoperative steroid injections in the surrounding tissue defect, amniotic membrane transplantation has a comparable recurrence rate to conjunctiva autograft.The application of mitomycin-C does not further reduce the recurrence rate according to some studies.  There are many conflicting reports regarding the rate of postoperative pterygium recurrence after the use of amniotic membrane. Amniotic membrane could be considered when the size of the operative defect would be problematic for direct closure or conjunctiva autograft. 
Reconstruction of the Conjunctiva Surface
In addition to pterygium surgery, Amniotic Membrane Transplantation (AMT) has been used for other conjunctiva reconstruction techniques. Conjunctiva tumors have been removed and the remaining defect was revised with amniotic membrane. Surgical use of AMT for the revision of scars and symblepharon have been reported. In cases of conjunctivochalasis that fail medical therapy, AMT has been used to reconstruct the ocular surface.Scleral melts have been treated in conjunction with cadaveric sclera and overlying AMT with good success.  One report indicates that a leaking trabeculectomy bleb can be revised with amniotic membrane. 
Limbal Stem Cell Deficiency
Amniotic membrane can be used in cases of partial and total limbal stem cell deficiency. In cases of total limbal stem cell loss AMT alone will not suffice and needs to be used in conjunction with allogeneic stem cell transplantation. For cases of partial limbal stem cell loss, amniotic membrane has shown to enhance epithelialization and improve vision with and without allogeneic limbal cell transplantation.
Newer techniques include using autologous and allogeneic stem cells cultivated in the laboratory on amniotic membrane and then transplanting this combined tissue onto severely damaged corneas with no endogenous stem cells.     
Amniotic membrane has been used for both infectious and sterile ulcers with thinning and perforation. For ulcers with significant tissue loss, amniotic membrane may be applied in layers to build thickness to the defect. Such an intervention is intended to retard protease activity and to provide bulk for the defect in the hopes of promoting faster healing and avoiding cornea transplantation. It can provide a temporizing measure before cornea transplantation or possibly suffice as a permanent treatment.
Many reports in the literature illustrate the use of human amniotic membrane harvested from placenta at the time of caesarean section and preserved until use on the ocular surface. Cryopreserved amniotic membrane is available and commonly used and retains the histological and morphological properties of fresh tissue. AMT can be surgically attached to the ocular surface by absorbable or non-absorbable sutures. Biological tissue adhesive has also been used to attach AMT to the ocular surface.
Allogeneic tissue has an implicit risk of infectious disease transmission. In general, amniotic membrane is procured from potential donors undergoing caesarean section who have been screened for communicable disease, such as: HIV, hepatitis and syphilis. The placenta is cleaned with a mixture of balanced salt solution, penicillin, streptomycin, neomycin and amphotericin B. The amnion is separated from the chorion by blunt dissection under sterile conditions, attached to nitrocellulose paper strips and stored in glycerol solution. The tissue is either stored in that solution for fresh use or cryopreserved at a temperature of -80 degrees Celsius. Currently, there are no published reports of communicable disease transmission from AMT.
One report exists of a sterile hypopyon after repeated transplantation of human amniotic membrane on cornea surface.
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