From womb to wound

Use of amniotic membrane to treat injuries is growing.

By Anny M.S. Cheng, MD and Scheffer C.G. Tseng, MD, PhD

Treatment of diverse ophthalmic diseases by amniotic membrane transplantation (AMT) was first used more than 70 years ago. In 2005, U.S. law went into effect governing tissue-based products, and scientific and commercial interest in the membrane’s healing properties began to grow.¹ Development of different methods of tissue preservation helped to spur interest as well.²

This article will discuss recent advances to aid in regeneration.

Mechanism of action

The amniotic membrane (AM) shares the same cell origin as the fetus. Anatomically, the AM is the innermost membrane enwrapping the fetus in the amniotic cavity and extends from the fetal membrane. Histologically, AM consists of a single epithelial layer, a thick basement membrane and an avascular stroma. These findings suggest that AM, like fetal tissue, might not only promote healing but also facilitate regeneration.³

Adult wound healing is heralded by marked inflammatory responses involving many inflammatory cellular infiltrations derived from innate and adaptive immune responses. This wound-healing process is characterized by inflammation (acute phase), granulation tissue formation (intermediate phase) and scarring (chronic phase). Nonresolving inflammation and other pathological states lead to excessive scarring or nonhealing wounds.

Clinical ophthalmic indications

Surgeons transplant AM as either a permanent surgical graft or a temporary biological bandage/patch (Tables 1 and 2). When used as a permanent graft, AM fills in the tissue defect so that host cells grow over or into the membrane, which will subsequently be integrated into the host tissue. This mode prevents scarring so as to restore tissue integrity and function, including vision. In this mode, AM can be used as a single layer or multiple layers that are secured to the host tissue either by sutures or with fibrin glue (Figure 1).⁴

Figure 1. Preoperative (A, C) and postoperative (B, D) of representative patients with AMT and sealing the gap in primary (A, B) and recurrent (C, D) pterygium, respectively. The caruncle morphology is restored after surgery and motility restriction is also corrected.

AM can also be used as a temporary biological bandage/patch (Figure 2) to suppress acute or chronic host tissue inflammation so as to promote healing with minimal scarring. Occasionally, a patch and a graft are used together — the patch acts as a protective shield to ensure epithelialization of the AM graft.^{5, 6} The sutureless approach:

• Shortens the surgical time

• Permits topical anesthesia

• Eliminates suture-induced inflammation.

Figure 2. AM as patch graft with suture.

More importantly, this approach facilitates easy-access patient care by immediately delivering AM’s biological actions without delay. As a result, the in-tandem usage could radically change outcomes that require acute intervention, like chemical burns as well as Stevens-Johnson syndrome/toxic epidermal necrolysis.

Corneal surface reconstruction

When used as a graft (single layer or multiple layers), AM restores stroma loss and promotes the healing of persistent corneal ulcers including neurotrophic keratopathy, corneal stromal thinning and descemetocele. Compared to the conventional surgical treatments including lamellar/full-thickness corneal transplantation, tarsorrhaphy and conjunctival flap, AMT offers the advantage of avoiding potential allograft rejection and postoperative astigmatism of tectonic corneal grafts.^4,7

If the patient requires corneal transplantation, concomitant AMT can improve the success rate by reducing inflammation. Corneal perforations from 0.5 to 5 mm treated by AMT with or without additional tissue adhesive are reported to achieve high success rates as well.^4,7

Severe bacterial keratitis requires immediate treatment with intensive topical broad-spectrum antibiotics, which are potentially toxic to the corneal epithelium and contribute to a prolonged corneal epithelial defect. AM soaked with antibiotics prolongs the bactericidal effect, counterbalances the epithelial toxicity and exerts as-yet unclear antimicrobial effect. For patients with symptomatic bullous keratopathy caused by corneal endothelial decompensation, AMT can ameliorate pain, prevent recurrent erosion and microbial superinfection. Considering its approach, AM is likely more desirable than conjunctival flaps or tarsorrhaphy as it preserves a cosmetically more acceptable appearance.

For eyes with partial limbal stem cell deficiency, the remaining limbal epithelial stem cells can be expanded by AMT following conjunctivalized epithelium debridement to reconstruct corneal surface. For eyes inflicted with total LSCD, the transplantation of limbal epithelial stem cells is required. AM’s therapeutic abilities to restore a healthy limbal stromal niche also help with the success of transplanted autologous or allogeneic limbal grafts.^4,7

PERMANENT GRAFT

Conjunctival surface reconstruction

The integrated AM can be a part of the ocular surface or a tissue plane underneath (Tenon substitute in tenoplasty, muscle sheath substitute in strabismus surgery, scleral flap of a trabeculectomy). AM can facilitate healing with less inflammation and minimal scarring compared to conjunctival graft following removal of large conjunctival lesions such as tumors. Suppression of postsurgical inflammation with AMT along with sealing the gap between the resected conjunctiva and the remaining Tenon capsule after fibrovascular excision helps to avoid pterygium recurrence (Figure 2).⁸ Also, AM can help reconstruct bulbar conjunctiva and fornix following lysis of symblepharon or conjunctivochalasis.^4,7

Biological bandage

Self-retained AM has been successfully used in conditions including refractory ulcerative keratitis, neurotrophic keratitis, recurrent epithelial erosion, high-risk corneal grafts, acute chemical and thermal burns, acute Stevens-Johnson syndrome/toxic epidermal necrolysis, necrotizing scleritis, and partial or total limbal stem cell deficiency.^4,9 A recent study suggested another: refractory dry eye disease (DED)(Figure 3).¹⁰ AM is rich in nerve growth factor which helps treat DED by reducing inflammation and may facilitate the return of corneal nerves.^11,12

However, self-retained AM also works as a magnet to attract inflammatory cells from the ocular surface. Repeated use of self-retained AM can facilitate the speed of reducing inflammation.

Persistent epithelial defect (PED) is usually neurotrophic, which disrupts the neural reflexes that control tear secretion and blinking, resulting in a severe form of dry eye, epithelial breakdown and poor healing. Conventional treatments usually fail to promote healing and tend to leave a corneal scar. If the epithelial defect has minimal or no stromal loss, AM can be used as a biological bandage — its active wound healing components and nerve growth factor facilitate epithelial healing and help recover corneal sensitivity.⁴ AM is expected to stay in place for two weeks for epithelization to occur. If the AM dissolves before this period during which PED shows minimal improvement, it may indicate the presence of ocular surface exposure because of infrequent lid blinking and/or incomplete lid closure. Self-retained AM also facilitates adequate blinking because of the polycarbonate ring that stimulates blinking.¹⁰ This likelihood also explains why placement of self-retained AM facilitates the ocular surface recovery in DED not only in the treated eye but also in the untreated fellow eye.

Recurrent corneal erosion, common in corneal dystrophies such as epithelial basement membrane dystrophy and granular dystrophy, is typified by defective basement membrane (BM) adhesions and recurrent epithelium breakdown. Conventional treatments have high recurrence rates and carry the risk of developing haze. AM, however, contains inhibitors of matrix metalloproteinases that prevent degradation of the basement membrane. Furthermore, AM also contains an active matrix component (see To Freeze, page 44)) that is essential for reducing inflammation and scarring and for promoting regenerative healing.

Conclusion

Use of AM is safe and effective for ocular surface reconstruction, with a very low infection rate. Ophthalmologists have found additional ocular tissue sites on which they can use AMT as a treatment; so too have other specialists found AMT useful in their clinical and surgical practices.¹ OM

This article was supported in part by an unrestricted grant from Ocular Surface Research Education Foundation, Miami, Fla.

Dr. Schell reports he spoke on behalf of Katena at AAO 2015.

REFERENCES

About the Authors
	Anny M.S. Cheng, MD, served as the director of the ophthalmology department at the National Taiwan University Hospital, Yunlin branch from 2007-2013. Since 2014 she has been the associate clinician scientist at the Ocular Surface Center, Miami, and participates in product development and clinical trials for TissueTech, Inc.
	Scheffer C.G. Tseng, MD, PhD cofounded Bio-Tissue, Inc. in 1997 and serves as the chairman and chief scientific officer of TissueTech, Inc. He served as chair professor at Bascom Palmer Eye Institute, University of Miami School of Medicine, until 2002. His research focus during the last 12 years has been to identify the active biological components of human amniotic membrane, to develop alternative products in delivering the efficacies of its natural healing properties and to expand the benefits of its clinical applications. Contact him at: stseng@ocularsurface.com
	Financial disclosure: Dr. Tseng is the founder and a major shareholder of TissueTech, Inc., which holds patents on the methods of preservation and clinical uses of amniotic membrane graft and ProKera.