MAMC Journal of Medical Sciences

REVIEW ARTICLE
Year
: 2015  |  Volume : 1  |  Issue : 3  |  Page : 126--130

Amniotic membrane in ophthalmology: A versatile wonder


Arushi Garg, Kirti Singh, Ankush Mutreja, Keerti Wali, Mainak Bhattacharjee 
 Division of Glaucoma, Guru Nanak Eye Centre, Maulana Azad Medical College, New Delhi, India

Correspondence Address:
Ankush Mutreja
241 DDA SFS Flats, Sector 9, Pocket 1, Dwarka, New Delhi - 110 045
India

Abstract

Amniotic membrane is a unique biological product that has been in use for a myriad of bodily conditions, both ophthalmic and non-ophthalmic. However, the ophthalmic use are still increasing day by day. Its unique properties like anti-inflammatory, antimicrobial, antifibrotic, antiangiogenic and source of growth factors make it into a biological bandage which can be life-saving to the eye. Harvested from the human placenta, it has found extensive use in ocular surface reconstruction, chemical injury to the eye, corneal perforation, persistent epithelial defects, ocular surface neoplasia, pterygium surgery, trabeculectomy, glaucoma bleb repair and lid surgeries, to name a few. This article outlines in detail the properties and utility of amniotic membrane.



How to cite this article:
Garg A, Singh K, Mutreja A, Wali K, Bhattacharjee M. Amniotic membrane in ophthalmology: A versatile wonder.MAMC J Med Sci 2015;1:126-130


How to cite this URL:
Garg A, Singh K, Mutreja A, Wali K, Bhattacharjee M. Amniotic membrane in ophthalmology: A versatile wonder. MAMC J Med Sci [serial online] 2015 [cited 2020 Oct 24 ];1:126-130
Available from: https://www.mamcjms.in/text.asp?2015/1/3/126/166298


Full Text



 Introduction



Amniotic membrane (AM) is the translucent innermost layer (amnion) of fetal membranes forming the placenta, attached loosely to the chorionic plate. Lately this unique biological product has achieved fame and a special place in the various sub-specialties of ophthalmology. Use of AM was first advocated by Davis in 1910 for skin transplantation.[1] Soon, reports emerged of its use as a dressing in burns,[2] nonhealing ulcers,[3] vaginal reconstruction,[4] repair of abdominal herniation,[5] and prevention of post-surgical adhesions.[6] Its use in ophthalmology was reported by Sorsby and Symons [7] way back in 1946.

 Histopathology



The structure of this ectodermal derivative comprises an inner layer of epithelial cells on a basement membrane, which is attached to a connective tissue membrane. The avascular membrane is about 0.02–0.5 mm thick and consists of five layers from within outwards:[8]

Epithelial monolayer of cuboidal or columnar cells Tough basement membrane of reticular fibers, which provide tensile strength. This basement membrane is one of the thickest human membranes and is resistant to current cryopreservation techniques. It closely resembles conjunctival basement membrane Avascular stroma composed of three layers: (a) Compact layer of a complex reticular network devoid of cells. (b) Fibroblast layer, the thickest layer of AM composed of fibroblasts in a loose reticular network. (c) Outermost spongy layer, forms the interface between amnion and chorion.

 Properties



Wound healing properties of AM and its influence on the local milieu depend on viability of cells in its structure. This gives rise to differences between freshly harvested AM and preserved AM, the latter being an inert tissue with little or no viable cells.

The properties of AM, which make it a viable option for use in the following conditions are further elaborated.

Tissue replacement

Transparency, structural integrity, and tensile strength make AM a favored tissue replacement in ocular surface reconstruction. It functions as a biological bandage to cover areas of denuded epithelium, stimulates healing, and relieves pain. Fresh AM has been found to harbor messenger Ribo Nucleic Acid (mRNA) for anti-angiogenic and anti-inflammatory factors.

Substrate for epithelial growth

Basement membrane of amnion contains collagen Type IV, V and VII along with fibronectin and laminin, similar to corneal and conjunctival basement membrane. Collagen Type V helps in anchorage of epithelial cells to stroma, whereas basement membrane promotes cell migration, adhesion, differentiation and prevents apoptosis of epithelial cells, thus facilitating re-epithelialization in persistent epithelial defects. It also promotes nongoblet cell differentiation of conjunctival epithelial cells. This property of AM has been utilized for in-vivo re-epithelialization of denuded epithelium as well as ex-vivo culture of epithelial sheets.

Source of growth factors

Both epithelium and stroma in fresh as well as preserved AM express mRNA for various growth factors, including epidermal, hepatocyte, basic fibroblast, transforming growth factor (TGF)-α and β-1,2,3, which promote epithelialization.[9]

Anti-inflammatory

AM expresses mRNA for interleukin-1 (IL-1) receptor antagonist and IL-10 cytokines, which are potent inhibitors of inflammation.[10] It also reduces neutrophilic infiltration and thereby keratocyte death. A barrier effect is provided and inflammatory cells are sequestered from the ocular surface.

Anti-fibrotic

AM is rich in fetal hyaluronic acid which suppresses TGF-β signaling pathway, thus preventing fibroblast activation. It also modulates production of actinin, suppresses tissue matrix metalloproteinases and keratocyte apoptosis, all of which inhibit scarring. This property is used when AM is utilized as a safer alternative to Mitomycin C (MMC) as an anti-fibrotic in glaucoma filtration surgery.

Anti-angiogenic

Its anti-inflammatory properties along with expression of certain anti-angiogenic factors such as thrombospondin, endostatin, and tissue inhibitors of metalloproteinases (TIMP) by epithelial and mesenchymal cells impart potent anti-angiogenic effects.

Anti-microbial

Both amnion and chorion demonstrate anti-microbial activity against Group A hemolytic streptococci, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa. Amniotic fluid also shows presence of anti-microbial factors such as bactericidin, betalysin, lysozyme, transferrin, lactoferrin, and IL-6. The barrier effect of the membrane contributes to its anti-bacterial effect.

Lack of immunogenicity

Amnion cells were initially believed to not express HLA-A, B, C, or DR antigen, making it immunologically inert. However, recent studies have shown that amnion epithelial and mesenchymal cells do express all Class 1 major histocompatibility complex (MHC) markers, but do not express any Class 2 MHC markers. Preserved human AM is immunologically inert, although fresh AM may induce a mild inflammatory reaction due to some viable cells.[11]

 Surgical Technique of Using the Amniotic Membrane



Fresh AM can be used freshly after harvesting from placenta of donor ensuring sero-negativity for communicable diseases such as HIV, hepatitis, and syphilis. This is usually possible with elective caesarean cases. The other method is to use commercially available AM cryopreserved at −80°C. Cells in both fresh and preserved AM are nonviable.

The membrane is utilized in three ways:

Inlay or graft: In this method AM is used as a scaffold (substrate) for surrounding epithelium to grow over. In the process AM gets incorporated into host tissue. The membrane needs to be tailored to size of defect and is anchored epithelium side up. It is used as such in cases of chronic, nonhealing epithelial defects Onlay or patch: In this method AM is used to cover raw ocular surface as a biological bandage to allow epithelialization to occur beneath it. Here, the membrane is applied epithelium side down and during the epithelialization process AM eventually falls off. The stroma acts as a mechanical barrier between inflammatory cells from ocular surface. It is used in this manner in cases of acute inflammation and is anchored to ocular surface with 8–0/10–0 vicryl or nylon sutures using quilting sutures after episcleral tacking around the limbus Filling in or layering: This is performed in cases with deep defects with stromal thinning where entire depth of defect is filled with small pieces of amnion and finally covered with larger patch graft.

The stromal side of the AM can be surgically differentiated from the epithelial side by the rough, sticky texture of the stroma, which raises vitreous-like strands to a dry merocel sponge, unlike the shiny and smooth appearance of the epithelial side.

 Indications of Amniotic Membrane Grafting



Ocular surface reconstruction

Acute chemical and thermal burns, toxic epidermal necrolysis, Stevens-Johnson syndrome

AM applied as a patch helps to restore corneal surface and clarity, reduce inflammation, promote re-epithelialization, relieve pain, prevent corneal and conjunctival scarring and formation of symblepheron. It gives best results if performed within 7–10 days of the acute event. It is commonly applied in cases with chemical injuries to the cornea in our country [Figure 1]A and [Figure 1]B.{Figure 1}{Figure 2}

Chronic ocular surface inflammation with limbal stem cell deficiency

This condition is seen in chronic ocular burns, ocular cicatricial pemphigoid (OCP) with ongoing inflammation, symblepheron formation, limbal stem cell deficiency (LSCD), and persistent epithelial defects. In all these conditions, AM is used in conjunction with limbal stem cell transplantation (LSCT) to reform corneal surface and promote re-epithelialization. After release of symblephera, AM is sutured into the fornices with fornix forming sutures and anchored up to the lid margin in order to form adequate fornices. It is also sutured to the limbus with episcleral bites and to bulbar conjunctiva for proper coverage. Patients with partial LSCD have been found to benefit from AM grafting alone, while those having total LSCD require both AM grafting and LSCT.[12]

Corneal surface restoration

Pseudophakic bullous keratopathy with epithelial erosions

For this condition AM is used as a patch graft for cases with poor visual potential as a palliative measure or as a temporary measure for cases with pseudophakic bullous keratopathy waiting for keratoplasty to relieve pain due to epithelial erosions.[13]

Persistent epithelial defects

Secondary to keratoconjunctivitis sicca, neurotrophic keratopathy and microbial keratitis. The underlying mechanism is LSCD and AM has been used successfully as an inlay graft to provide a substrate for epithelium to grow, or as an onlay patch to facilitate epithelialization by acting as a bandage against inflammation.[14]

Corneal perforation

It has been used in conjunction with tissue adhesives (cyanoacrylate glue and human fibrin glue) to seal small nontraumatic corneal perforations.[15],[16]

Corneal ulcers, peripheral ulcerative keratitis

It has been successfully used to treat nonhealing corneal ulcers in the form of a multi-layered filler to fill the crater and covered with an inlay graft, followed by an onlay patch.[17] The anti-inflammatory, anti-microbial and anti-angiogenic, effects of AM are employed to reduce inflammation and buy time before keratoplasty, or to reduce progression of stromal lysis in bacterial and herpetic ulcers [18] [Figure 2].{Figure 3}

Recurrent corneal erosions

AM has been investigated for use in recurrent corneal erosions to aid epithelialization.[19]

Shield ulcers in vernal keratoconjunctivitis

AM grafting combined with surgical debridement of mucus plaque has been shown to be very effective in treatment of shield ulcers.[20] The membrane promotes epithelialization and improves cell adhesion to basement membrane.

Band-shaped keratopathy

Use of AM with superficial keratectomy and Ethylenediaminetetraacetic acid (EDTA) application has proved to stabilize the ocular surface, reduce epithelial irregularity, and relieve pain.[21]

Photorefractive and phototherapeutic keratectomy

Animal models have shown that Amitotic membrane transplantation (AMT) following photorefractive keratectomy (PRK) reduces inflammation, corneal haze, and stromal infiltration without affecting epithelial healing.[22] One human study has shown moderate effect of AMT with phototherapeutic keratectomy in reducing corneal haze, subepithelial fibrosis and regression following PRK.[23]

Ex-vivo expansion of limbal epithelial cells

The de-epithelialized basement membrane of amnion serves as an effective substrate for corneal limbal epithelial cells to grow and form an epithelial sheet due to increased epithelial cell adhesion. A small 2 mm × 2 mm explant of limbal stem cells is cultured on an acellular amnion carrier using human corneal epithelial cell medium, 10% fetal bovine serum or autologous serum for 10–15 days. This produces an expanded epithelial sheet when an adequate sized (4–6 clock hours) limbal autograft is not available (in cases with bilateral LSCD with limited healthy limbus available). This cultured epithelium when transplanted onto the corneal surface gets easily integrated into host tissue, reduces risk of iatrogenic LSCD in donor eye, is easy to handle, and gives excellent outcomes.[24]

Conjunctival reconstruction

Symblepheron and cicatrizing conditions of conjunctiva

In cicatricial disorders of conjunctiva like OCP, cicatrizing conjunctivitis, Steven-Johnson syndrome and symblepheron, AM has shown favorable outcomes in reformation of fornix, preventing recurrence of symblepheron, restoring ocular surface, providing cosmesis, and improving patient comfort.[25]

Ocular surface squamous neoplasia and conjunctival tumours

It has been utilized for conjunctival reconstruction after extensive resection of conjunctiva for benign and maligmant ocular surface tumors, including ocular surface squamous neoplasia (OSSN), conjunctival melanoma, lymphoma and even conjunctivochalasis. Use of AM allows larger conjunctival resections to be made, allows better detection of tumor recurrence underneath, reduces donor site morbidity and improves cosmesis. Long-term results of management of OSSN with partial sclerectomy, alcohol epitheliectomy, conjunctival resection, cryotherapy, application of MMC, and conjunctival reconstruction with AM transplant have shown excellent results.[26]

Pterygium

First reported after pterygium surgery in 1997, use of AM reduced recurrence rate of the condition when compared with conjunctival autografts.[27] AM grafting has been selectively advocated either in combination with conjuctival autograft (CAG) or limbal cell autograft (LCAT), especially in recurrent cases, or in primary double-headed pterygium, or when there is a need for extensive resection or preserving the superior conjunctiva for future glaucoma surgery [Figure 3].{Figure 4}

Glaucoma surgery

AM has been used as an alternative to standard anti-fibrotic agents like MMC in glaucoma filtration surgery to prevent scarring under the scleral flap or inner wall of the bleb. It reduces fibroblast growth and delays healing response in rabbit models.[28] Intraocular pressure control is similar to that using MMC, with better morphology, reduced vascularity and increased longevity of the bleb [Figure 4].{Figure 5}

The membrane has also been used as an adjunct to cover glaucoma valve implants and in trabeculectomy in cases with conjunctival scarring and shortening. The use of AM as an alternative to conjunctival advancement has been studied in repair of bleb leakage [29],[30] and has been found to be a suitable alternative in the long-term, although the blebs repaired with AM alone are thinner and more prone to early re-leakage [Figure 5].{Figure 6}

Lid and orbital surgeries

Cicatricial entropion

It has been used in surgical correction of cicatricial entropion secondary to trachoma, OCP, thermal or chemical burns to cover bare tarsus in a lid-split procedure to ensure re-epithelialization.[31]

Other uses

It has been used to replace conjunctiva in lid reconstruction, to prevent extrusion of orbital implant, in punctal occlusion and in reconstruction of grade 2 and 3 contracted sockets.[32]

 Precautions



AM grafting is however not without its share of risks. Suture granulomas, premature dissolution of membrane, mild immunological reaction with fresh AM, calcification, and transmission of viruses and bacteria (more with fresh AM than cryopreserved AM) are some complications that have been occasionally experienced. Over a decade of use in the ophthalmology department the authors have not noted any of the above mentioned complications with use of cryopreserved commercially available AM.

Recently, self-retained suture-free AM (Prokera; Bio-Tissue, Inc.,) has been developed, which is still undergoing research. It consists of a piece of cryopreserved AM assembled inside a polymethylmethacrylate symblepheron ring, the stromal side facing the cornea. It can be worn over the cornea as a symblepheron ring, and delivers all the therapeutic benefits of AM.

 Conclusion



AM transplantation is a safe and effective modality of treatment for a large variety of ophthalmic disorders and a panacea for many vision-threatening conditions. Its field of application is increasing day by day. Newer methods are being researched in order to improve its application to the ocular surface and delivery of therapeutic benefits and to make it more comfortable for the patient.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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