Amniotic Membrane for the Eye: Tissue and Surgical Methods

Amniotic membrane has become a valuable tool in ophthalmology due to its ability to promote healing and reduce inflammation. Derived from the innermost layer of the placenta, it provides a biologically active surface that supports tissue regeneration, making it effective for treating various eye conditions.

Its use in ocular procedures has expanded with advancements in preservation techniques and surgical applications. Understanding how this tissue is processed and applied clarifies its benefits and limitations in clinical practice.

Tissue Composition And Structure

The amniotic membrane consists of three primary layers: the epithelium, basement membrane, and stroma. The epithelial layer, often removed during processing, contains progenitor cells that aid tissue regeneration. Beneath it, the basement membrane serves as a scaffold for epithelial cell migration, closely resembling the native basement membrane of the cornea and conjunctiva. This similarity enhances cellular adhesion and proliferation, making it particularly useful in reconstructive eye procedures.

The stromal layer, the thickest component, is rich in extracellular matrix proteins such as collagen types I, III, IV, and VII, which provide tensile strength and structural integrity. It also contains glycoproteins and proteoglycans that regulate hydration and create an optimal healing environment. Additionally, the stroma harbors bioactive molecules, including epidermal growth factor (EGF), transforming growth factor-beta (TGF-β), and hepatocyte growth factor (HGF), which modulate inflammation, promote epithelialization, and inhibit fibrosis. These properties help reduce scarring and enhance corneal surface restoration.

A significant feature of the amniotic membrane is its low immunogenicity, due to the absence of vascularization and antigen-presenting cells. This allows it to be used as a graft with minimal risk of rejection. Anti-inflammatory cytokines such as interleukin-10 (IL-10) and tissue inhibitors of metalloproteinases (TIMPs) further suppress excessive inflammation and prevent extracellular matrix degradation, fostering ocular surface healing while minimizing complications.

Collection, Preparation, And Storage

Amniotic membrane is obtained from donor placentas from healthy individuals undergoing elective cesarean sections, minimizing microbial contamination and ensuring tissue integrity. Donor screening follows stringent guidelines set by regulatory bodies such as the U.S. Food and Drug Administration (FDA) and the American Association of Tissue Banks (AATB). This includes serological testing for infectious diseases like HIV, hepatitis B and C, and syphilis, along with maternal medical history assessments to ensure safety.

Once collected, the placenta is transported under sterile conditions to a processing facility, where the amniotic membrane is carefully separated from the chorion. This dissection requires precision to preserve the basement membrane, which facilitates epithelial adhesion and migration. The isolated tissue undergoes multiple washes with balanced salt solutions containing antibiotics and antifungals to eliminate contaminants. Some protocols incorporate additional decontamination steps using broad-spectrum antimicrobial agents or gamma irradiation, though these must balance microbial safety with preserving bioactive components.

Preservation techniques vary based on intended use, with cryopreservation and dehydration being the most common. Cryopreservation stores the membrane at ultra-low temperatures with cryoprotectants like dimethyl sulfoxide (DMSO) or glycerol to prevent ice crystal formation, preserving biological activity. Dehydration methods, such as air-drying or lyophilization, extend shelf life and simplify storage but may alter biomechanical properties, necessitating rehydration before use.

Types For Ophthalmic Use

Preservation methods influence the structural integrity and biological activity of the amniotic membrane, determining its suitability for different ophthalmic applications. The three primary forms used in clinical practice are cryopreserved, dehydrated, and reconstituted, each offering distinct advantages and limitations.

Cryopreserved

Cryopreserved amniotic membrane is stored at ultra-low temperatures with cryoprotectants like glycerol or DMSO to prevent ice crystal formation. This method preserves the extracellular matrix and bioactive molecules, including EGF and TGF-β, which promote epithelialization and modulate inflammation. Studies show that cryopreserved membranes retain high biological activity, making them effective for treating persistent epithelial defects, corneal ulcers, and chemical burns. However, the need for specialized freezing equipment and controlled thawing can limit accessibility in some clinical settings. While prolonged freezing may degrade some bioactive components, cryopreserved amniotic membrane remains a preferred choice for cases requiring maximal regenerative potential.

Dehydrated

Dehydrated amniotic membrane undergoes air-drying or lyophilization to remove moisture, allowing extended shelf life at room temperature. It is often packaged in a sterile, ready-to-use format, making it convenient for surgical and office-based applications. While dehydration preserves the collagen matrix, some bioactive factors may be reduced or altered. Despite this, dehydrated membranes still provide significant anti-inflammatory and anti-scarring benefits, making them useful for pterygium surgery, conjunctival reconstruction, and dry eye disease. Rehydration is required before application, and handling characteristics may differ from cryopreserved versions, with some clinicians noting increased stiffness. Nevertheless, the ease of storage and availability make dehydrated amniotic membrane a practical option for various ophthalmic procedures.

Reconstituted

Reconstituted amniotic membrane is derived from processed amniotic tissue that has been enzymatically or chemically treated to create a biologically active matrix. This form is often used in amniotic membrane extracts, eye drops, or bioengineered scaffolds for targeted ocular therapies. Unlike intact membranes, reconstituted formulations deliver soluble growth factors and extracellular matrix components in a controlled manner. Research has explored their potential in treating neurotrophic keratitis and severe dry eye disease, where bioactive molecules enhance corneal healing. However, processing methods can alter the membrane’s native structure, and therapeutic efficacy may vary. While still an emerging area, reconstituted amniotic membrane products represent a promising avenue for expanding clinical applications.

Surgical Methods

The integration of amniotic membrane into ophthalmic surgery requires precise placement to maximize its therapeutic potential. Techniques vary depending on the severity and location of the ocular defect, with the membrane serving as either a temporary dressing or a permanent graft. When used as a patch, it is placed epithelial side up, allowing bioactive components to modulate inflammation and promote epithelial migration without direct tissue incorporation. This method benefits acute conditions such as chemical burns and persistent epithelial defects, where immediate surface protection and anti-inflammatory effects are needed. When applied as a graft, the stromal side contacts the ocular surface, facilitating cellular integration and long-term structural support. This approach is used for corneal thinning, conjunctival reconstruction, and ocular surface stem cell deficiency.

Securing the membrane impacts surgical outcomes. Traditional suturing with absorbable sutures provides stability but can cause irritation and prolong recovery. Fibrin glue has become a preferred alternative, offering secure attachment while reducing surgical time and postoperative discomfort. Studies show that fibrin-based adhesives enhance graft adherence and minimize inflammation, particularly in pterygium excision and conjunctival reconstruction. Additionally, newer sutureless techniques using self-retaining amniotic membrane devices enable in-office applications for conditions such as dry eye disease and neurotrophic keratitis, eliminating the need for surgical fixation.

Indications In Ocular Procedures

Amniotic membrane is used in a variety of ophthalmic treatments due to its regenerative properties and ability to modulate inflammation. It addresses both acute injuries and chronic degenerative conditions, with application guided by the severity of epithelial damage, stromal involvement, and risk of scarring. By providing a biologically active scaffold, it facilitates epithelial migration, suppresses excessive inflammation, and supports long-term tissue remodeling.

One of its most well-documented applications is in managing persistent epithelial defects and corneal ulcers, where standard therapies may fail to promote re-epithelialization. Studies show that amniotic membrane transplantation accelerates healing by maintaining hydration and releasing growth factors that stimulate epithelial proliferation. In chemical and thermal burns, early intervention reduces stromal melting and prevents limbal stem cell deficiency, which can lead to severe ocular surface instability. It also aids conjunctival reconstruction after pterygium or symblepharon excision, lowering recurrence rates by modulating fibroblast activity. Emerging research continues to explore its efficacy in neurotrophic keratitis, Stevens-Johnson syndrome, and severe dry eye disease, broadening its therapeutic applications in ophthalmology.