The amniotic membrane (AM) is the innermost layer of the placenta, a thin, translucent tissue that encloses the developing fetus. Its natural function is to form the amniotic sac, providing a protective barrier against trauma and infection while facilitating fetal growth. This tissue promotes a regenerative environment, making it a valuable resource in medicine. It was first used for skin grafting in the early 1900s. Its use in ophthalmology began in the 1940s for ocular surface reconstruction, with widespread adoption occurring after the 1990s following the development of modern preservation techniques.
Biological Healing Properties
The therapeutic effect of the amniotic membrane (AM) promotes healing without scarring through cellular and molecular actions. A significant mechanism is its potent anti-inflammatory action, mediated partly by heavy chain hyaluronic acid/pentraxin 3 (HC-HA-PTX3) in the extracellular matrix. This complex suppresses the activation and migration of inflammatory cells, such as neutrophils and lymphocytes, at a wound site. The AM’s cells also secrete factors that encourage macrophages to switch from a pro-inflammatory (M1) to an anti-inflammatory (M2) state, helping to resolve swelling and redness.
The amniotic membrane actively prevents the formation of scar tissue, known as fibrosis, which can cloud the cornea and impair vision. It inhibits the activity of fibroblasts, the cells responsible for depositing excessive collagen that leads to scarring. The tissue contains anti-fibrotic molecules, such as tissue inhibitors of metalloproteinases (TIMPs) and transforming growth factor-beta 3 (TGF-β3). TGF-β3 is important because it counteracts TGF-β1, a molecule that stimulates scarring, promoting regeneration similar to scarless fetal healing.
The membrane functions as a regenerative scaffold, providing an ideal substrate for the growth and migration of the eye’s epithelial cells. The AM’s epithelial layer contains a basement membrane rich in structural proteins like laminin and collagen. This structure closely resembles the natural basement membrane of the cornea, acting as a physical anchor for the patient’s epithelial cells to spread and cover the defect. The AM is also a reservoir of growth factors that stimulate the proliferation and differentiation of these cells, accelerating the resurfacing of the damaged ocular surface.
Conditions Treated
Amniotic membrane transplantation is a proven treatment for a wide range of ocular surface diseases and injuries that resist conventional therapies.
The AM is used to treat:
- Persistent epithelial defects (PEDs), which are non-healing corneal wounds that risk infection or perforation. The AM acts as a biological bandage, shielding the defect while promoting cell migration.
- Severe surface damage caused by chemical or thermal burns, mitigating inflammation and scarring that can lead to vision loss.
- Non-infectious corneal ulcers, providing structural support to thinning tissue and encouraging ulcer closure.
- Pterygium, a fleshy growth on the conjunctiva. The AM is employed during surgical removal to reconstruct the surface and reduce the likelihood of recurrence.
- Severe dry eye syndrome unresponsive to standard treatments, stabilizing the ocular surface by providing a regenerative environment.
Preparation and Application Methods
The therapeutic material is sourced from the placenta of healthy, screened donors following elective Cesarean sections. Strict protocols test the donor tissue for transmissible diseases, ensuring the final product is safe for human transplantation. The membrane is preserved using one of two methods: cryopreservation or lyophilization. Cryopreservation involves freezing the tissue in a solution, which retains more biologically active components, such as growth factors and the anti-inflammatory HC-HA-PTX3 complex. Lyophilization, or freeze-drying, results in a thinner, more shelf-stable product, though it may alter some of the tissue’s natural biological properties.
The application technique depends on the specific ocular condition being treated, generally falling into two categories.
Surgical Grafting
For deep, chronic defects requiring long-term structural support, the membrane is applied as a surgical graft. It is secured with fine sutures or fibrin glue, acting as a permanent basement membrane substitute that is slowly incorporated into the host tissue.
Sutureless Application
For less severe or temporary conditions, a sutureless application is often used. The AM is mounted onto a conformer ring, sometimes described as a biological contact lens. This self-retaining device can be placed in an office setting, providing a temporary protective and healing barrier. The membrane is naturally resorbed by the body over a period ranging from a few days to several weeks, depending on the preservation method and the defect’s severity.