Amniotic membrane embraced as versatile treatment for ocular surface disease

Several decades after its initial use, amniotic membrane transplantation has been embraced by many ophthalmologists as a safe, versatile and largely efficient method of treating ocular surface diseases and other conditions.

Amniotic membrane transplantation is used in conjunction with surgical procedures involving the cornea, conjunctiva and limbus. It is also used to support local tissues in glaucoma bleb surgery, strabismus surgery and orbital reconstruction.

Amniotic membrane, or amnion, is the inner layer of the placenta and comprises a thick basement membrane and avascular stromal matrix. It is currently available in cryopreserved and freeze-dried forms. It is avascular and biocompatible with multiple tissue types on the ocular surface.

Amniotic membrane transplantation was first used for ocular surface reconstruction following chemical injury in the 1940s but yielded inconsistent results. However, it was virtually rediscovered in the mid-1990s and has since been used in a growing range of indications. Amnion has largely supplanted autologous buccal mucosa harvested from the mouth and other allogenic tissue products.

Amnion can be used as a graft material or bandage contact lens to promote healing and minimize inflammation, as a scaffold to cultivate stem cells, or as a structural reinforcement material.

Corneal indications include persistent epithelial defect, recurrent epithelial erosion, corneal ulcer and perforation, inflammatory and infectious keratitis, bullous and band keratopathy, limbal stem cell deficiency, high-risk corneal graft, chemical injury, Stevens-Johnson syndrome and abnormal scarring after superficial keratectomy.

Amnion is a user-friendly tissue with great applicability, according to Kenneth R. Kenyon, MD. Image: Ashley Brito-New England Eye Center

Indications in conjunctival reconstruction are pterygium, symblepharon, conjunctivochalasis and tumors.

For some surgeons, amniotic membrane transplantation has supplanted conjunctival flaps and autografts as the preferred technique for repairing defects created by excision of pterygia or conjunctival tumors.

Sutureless grafting techniques, utilizing tissue adhesives, and other ongoing innovations promise to boost amniotic membrane as a primary and adjunct treatment in challenging or high-risk cases.

“Amniotic membrane is a unique tissue graft that is capable of promoting wound healing through sophisticated biological pathways,” Scheffer C.G. Tseng, MD, PhD, a leader in the biologics industry, said.

Thomas John, MD, OSN Cornea/External Disease Board Member, said amnion can be a viable alternative to native tissue in select cases.

“There will be a need to ensure coverage when the patient’s own conjunctiva is not available or the surgeon prefers not to use that tissue,” Dr. John said. “Then, amniotic membrane is a good source to surgically repair various conditions.”

Amnion is versatile and easy to use, Kenneth R. Kenyon, MD, OSN Cornea/External Disease Editor Emeritus, said.

“Mother Nature did a good thing when she gave us amnion. It’s a very user-friendly tissue that has great applicability,” Dr. Kenyon said. “Amnion has great utility for major ocular surface applications, especially in the settings of persistent epithelial defects, noninfectious corneal ulcers, and as a carrier or overlay for limbal stem cell grafts.”

Amnion’s safety is supported by a 20-year track record, careful screening protocols and strict quality control measures, Dr. Kenyon said.

“The donors are screened with the same rigor as are cornea donors,” he said. “The amnion is harvested during cesarean section and is kept preserved until the mother’s testing for hepatitis, HIV and other communicable disease testing are proven negative before its use. I’m not aware of any case of human disease being transmitted via an amnion graft. Bottom line, there’s no transmissible disease risk, even potentially, with amnion.”

Dr. Kenyon said he prefers fresh frozen tissue as opposed to freeze-dried material. He said his enthusiastic use of amnion in non-healing corneal surface disorders is balanced by his preference for conjunctival autografts in more straightforward situations, such as pterygia.

Amnion has various biochemical and biomechanical attributes that bolster its safety and applicability, Amar Agarwal, MS, FRCS, FRCOphth, OSN Asia-Pacific Edition Board Member, said.

Amar Agarwal

“Amniotic membrane is used for its anti-inflammatory and anti-angiogenic properties as well as its ability to promote epithelial differentiation, adhesion and migration,” Dr. Agarwal said. “It also has antibacterial, wound-protecting, pain-reducing and fibrosis-suppressing effects. It can be used as a graft where it fills defects and promotes epithelialization, or it can be used as a patch where it is used for its anti-inflammatory and anti-angiogenic properties. It may also be used as a patch-graft simultaneously according to the underlying condition being treated.”

Although the biomechanics and chemical composition of amniotic membrane are largely unknown, it is still highly desirable for a number of reasons, Dr. Agarwal said.

“It is easily obtainable, is relatively cheap and is easy to manipulate. Despite being an allograft, it has low immunogenicity and therefore does not cause rejection,” he said.

The cost of amniotic membrane compares favorably with that of other commercially available tissues, Dr. Tseng said.

“Amniotic tissue is more expensive, however, than autologous tissue such as buccal mucosa, as the amniotic tissue must be processed to follow [U.S. Food and Drug Administration] regulations as well as to ensure biological efficacy,” he said.

Amnion is eligible for Medicare and other reimbursement in many of its ocular surface indications, Dr. Kenyon said.

“As for the coding aspects, I believe it has been reasonably and appropriately defined in the U.S.,” he said.

Cornea and conjunctiva

Amniotic membrane is especially well-suited for use as an overlay graft or inlay graft, Dr. Kenyon said.

“From my perspective, amnion is especially useful as an adjunct to ocular surface surgery, No. 1 as a large-diameter overlay graft to assist with limbal allograft or in some cases autograft transplantation, and also as smaller-diameter inlay grafts in one or more layers to promote the healing of sterile corneal stromal ulcers and persistent epithelial defects,” he said.

Amniotic membrane has been used for persistent epithelial defects secondary to neurotrophic corneas, autoimmune disorders and limbal stem cell deficiency, Dr. Agarwal said.

“In these cases, amniotic membrane may act by inhibition of collagenases while at the same time providing collagen and a basement membrane for epithelial cells to grow on,” he said. “The amniotic membrane also provides growth factors, all of which provide a conducive atmosphere for epithelial cells to grow on.”

Amniotic membrane is used as a graft to fill the defect and replace stromal matrix loss in small corneal of scleral melts. Necrotic tissue and loose epithelial tissue are removed from the defect. Larger areas of melt require additional tissue replacement such as donor scleral patch graft, which in turn may be covered by amniotic membrane.

“This onlay provides anti-inflammatory effects and promotes wound healing,” Dr. Agarwal said.

Amniotic membrane grafts are also used to treat bullous keratopathy secondary to surgery or Fuchs’ dystrophy, Dr. Agarwal said.

According to Dr. John, clinicians should seriously consider using amniotic membrane when appropriate in cases of toxic epidermal necrolysis, a more severe form of Stevens-Johnson syndrome.

Thomas John

In 2002, Dr. John and colleagues published in Ophthalmology the first report on the use of amniotic membrane to treat toxic epidermal necrolysis, showing that a patient with this condition who underwent amniotic membrane transplant had 20/20 vision and normal tear function after 13 years of follow-up.

“If you never did that, there would be a good chance of losing vision and even losing the eye,” Dr. John said.

Many patients with toxic epidermal necrolysis or Stevens-Johnson syndrome undergo traditional treatment, which involves application of a lubricant and breaking of adhesion between the eyelids and the eye.

“You’re losing precious time because, after the first 10 to 14 days, you lose the opportunity to actually prevent the ongoing destructive process over time,” Dr. John said.

Amniotic membrane transplantation should be performed within 10 to 14 days of diagnosis, Dr. John said.

“Most emergency room physicians, internists and pediatricians who are in the front lines don’t really recognize this,” he said. “There are also a lot of ophthalmologists and eye care providers who are not aware that the timing is so important. This is really huge. To get this message out is of paramount importance. It is a difference between losing one’s eyesight and preserving one’s vision.”

Dr. Agarwal said that amniotic membrane has been shown to reduce the recurrence of pterygia, particularly in patients who lack sufficient conjunctival tissue for grafting.

“Nevertheless, conjunctival autograft has been shown to have a lower incidence of postoperative inflammation and recurrence than amniotic membrane transplantation,” Dr. Agarwal said.

Dr. Kenyon said that the efficacy of amniotic membrane vs. conjunctival autograft in pterygium surgery is uncertain.

“I realize that there are also schools of thought that like amnion for pterygium surgery, but having been involved for many years with conjunctival autograft technique, there is still no study that proves amnion to be superior,” Dr. Kenyon said. “Given its significant costs, I think my opinion is widely shared that conjunctival autografting is economically as well as clinically superior to amnion.”

Glaucoma, strabismus surgery

Amniotic membrane transplantation is used in glaucoma treatment as a spacer to reduce scarring in trabeculectomy, as a temporary patch or permanent graft to repair leaking blebs or fill in conjunctival tissue, and as a conjunctival replacement or tube covering in cases involving glaucoma tube exposure.

“I have used amnion on occasions to reinforce leaking blebs and to cover shunt tubes and the like,” Dr. Kenyon said. “But I must say that in that scenario, I do not think it is as useful as either conjunctival bridge and free grafts or as pericardium or preserved lamellar corneal tissue in reinforcing the thin conjunctival tissues.”

The downside is that amnion is neither strong nor durable enough to serve effectively in these situations that require a permanent structural reinforcement, Dr. Kenyon said.

“Amnion doesn’t have much tensile strength and certainly doesn’t have a great deal of staying power, so it is not a great substitute for settings where you really need to have a durable reinforcement for conjunctiva,” he said.

Dr. Tseng noted that thick membrane options with high tensile strength, such as AmnioGuard (Bio-Tissue), can be used in glaucoma surgery.

Bleb excision surgery may involve a lack of conjunctival tissue to construct a conjunctival autograft to cover the bleb excision site, Dr. Agarwal said.

“Excision of the bleb and direct re-suturing, conjunctival advancement or conjunctival autografts may be used, but these depend on availability of adequate mobile conjunctiva to cover the defect without shortening the fornix,” he said.

A bleb can be closed with an amniotic membrane graft, although superior results have been reported with conjunctival advancement.

“The amniotic membrane is used to cover the defect after excising the area of thin, avascular conjunctiva,” Dr. Agarwal said.

Dr. Kenyon also expressed mixed feelings about the use of amnion in strabismus surgery.

“Clearly, it does have some role. Some surgeons even use it to wrap a surgically operated rectus muscle to prevent it from adhering to the globe,” Dr. Kenyon said. “Again, I find that conjunctival free grafting works very well in these situations just for the same reasons that I find it preferred in pterygium surgery.”

Amnion as substrate material

Recent innovations include amniotic membrane being used to cultivate limbal stem cells, Dr. Kenyon said.

“As far as utilization of the grafts, probably the most novel new application is for ex vivo expansion grafts of limbal stem cells, where amnion can be used as a substrate for small explants of limbus to be grown out, either in a tissue culture setting or in an ‘amnion sandwich’ placed on the eye with very small explants of limbal autograft tissue that is allowed to spread between the lamellae of amnion,” Dr. Kenyon said. “That’s a very clever way of performing limbal stem cell autografting.”

Amnion is safe by virtue of being biologically inert and pliable, Dr. Agarwal said.

“The amniotic membrane is non-immunogenic and does not contain any actively replicating cells. It promotes epithelial adhesion and migration,” he said. “Hence, it is an ideal substrate for ex vivo expansion of limbal stem cells obtained via a small biopsy from the patient’s eye. Once expanded on the amniotic membrane sheet, this can be used to transfer the limbal stem cells to the patient’s eye. It has the advantage of not leading to iatrogenic limbal stem cell deficiency in the donor eye, as only a small biopsy is required.”

Dr. Tseng said that amnion can be a substrate for the cultivation of progenitor cells for conjunctival epithelium, corneal epithelium and limbus, oral mucosa and corneal endothelium.

“Currently this composite tissue is being transplanted to restore vision as well as the structure and the function of damaged ocular surfaces in humans,” Dr. Tseng said. “Further investigation should help us unravel other therapeutic potentials in the fields of reconstruction, tissue engineering and regenerative medicine.”

Tissue-cultured human amniotic epithelial cells are also in use, Dr. Agarwal said.

“Corneal collagen sheets seeded with amniotic epithelial cells obtained from human donor placentas are cultured ex vivo and have been used for treatment of various conditions such as persistent epithelial defects,” he said. “The advantage of this technique is that it is repeatable, fast, easy to perform and does not involve surgery.”

Fibrin glue, sutureless grafting

After excision of pterygium or malignant tumors, some surgeons prefer to affix amniotic membrane grafts with sutures while others prefer fibrin glue. Generally, smaller conjunctival flaps can be used to cover tumor excision sites, while amniotic membrane is used to graft larger defects resulting from the removal of larger tumors. Some surgeons use conjunctival autografts or advancement flaps with dissolvable sutures to cover pterygium removal sites.

Fibrin glue facilitates adhesion of amnion to the ocular surface, Dr. Kenyon said.

“It doesn’t have a great deal of tensile strength, but it’s still adequate, for example, to hold an amnion graft or, for that matter, a conjunctival graft in place for pterygium surgery or for larger diameter overlays in ocular surface stem cell grafting,” he said.

Sutureless amniotic membrane transplantation is gaining momentum because of its convenience and efficacy, Dr. Tseng said.

Scheffer C.G. Tseng

“There is a growing interest in performing sutureless amniotic membrane transplantation to decrease tissue manipulation and increase the surgical efficiency,” he said. “In this regard, fibrin glue is used in lieu of sutures to improve the outcome and avoid suture-related complications.”

Dr. John said fibrin glue can be used as a means to minimize suturing of transplanted tissue.

“Even at the present time, the combined use of amniotic membrane with tissue adhesive, I think, will continue to increase in popularity,” Dr. John said. “It decreases the number of sutures being used. As you know, sutures can be a source of inflammation, irritation, discomfort and pain. Although, in my opinion, you cannot completely eliminate sutures.”

One downside to fibrin glue is that edges of the glued area can detach; a judicious amount of suturing would be warranted in such a case, Dr. John said.

“Having a few sutures will help,” he said. “The combination of using amniotic membrane along with tissue adhesives is a good way to do these procedures. In addition to increasing the patient’s comfort, one may want to use a contact lens on the ocular surface. And, of course, you have to cover with topical antibiotics to prevent any potential ocular infection.”

Bandage contact lens, eye drop

The amnion-based product pipeline includes the ProKera bandage contact lens (Bio-Tissue), which underwent an FDA clinical trial among military personnel at the Walter Reed Army Medical Center. According to ClinicalTrials.gov, the device facilitated complete corneal re-epithelialization.

The ProKera device is comprised of cryopreserved amniotic membrane clipped into a thermoplastic ring set. Primary indications are corneal epithelial defects, high-risk corneal transplants, infectious keratitis and penetrating keratoplasty, according to the company’s website.

Dr. Kenyon said that ProKera is easy to insert and precludes the need for surgery.

“[The ProKera amnion] is clever because it allows the amnion to be slipped in much the way that a large contact lens would be. This obviates the need for going to the [operating room] for suturing or gluing,” Dr. Kenyon said.

ProKera can be applied in various clinical settings, Dr. Tseng said.

“The clinical efficacy of ProKera is highlighted in cases with severely compromised eyes such as acute chemical burns, acute Stevens-Johnson syndrome and infectious keratitis,” he said. “ProKera can also be used to treat persistent or recurrent epithelial defects and other diseases where suppression of inflammation and re-epithelialization of the corneal surface are necessary.”

Dr. Kenyon and colleagues at Keera, a biologic/pharmacologic firm in Italy, have developed lyophilized amnion membrane extract, an amnion-derived eye drop designed to treat persistent corneal defects secondary to herpes simplex or zoster, trigeminal nerve defect or diabetes. The product has successfully undergone clinical trials in Italy and is slated to enter the market in the European Union in the near future.

“It’s very exciting work,” Dr. Kenyon said. – by Matt Hasson

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References:

• Barton K, Budenz D, Khaw PT, Tseng SCG. Glaucoma filtration surgery using amniotic membrane transplantation. Invest Ophthalmol Vis Sci. 2001;42(8):1762-1768.
• Gregory DG. Treatment of acute Stevens-Johnson syndrome and toxic epidermal necrolysis using amniotic membrane: a review of 10 consecutive cases. Ophthalmology. 2011;118(5):908-914.
• Habot-Wilner, Z, Spierer A, Barequet IS, Greenbaum A. Use of amniotic membrane graft and corneal transplantation in a patient with bilateral keratomalacia induced by uncontrolled phenylketonuria. Cornea. 2007;26(5):629-631.
• John T, Foulks GN, John ME, Cheng K, Hu D. Amniotic membrane in the surgical management of acute toxic epidermal necrolysis. Ophthalmology. 2002;109(2):351-360.
• Kenyon KR. Amniotic membrane: mother’s own remedy for ocular surface disease. Cornea. 2005;24(6):639-642.
• Miri A, Al-Deiri B, Dua HS. Long-term outcomes of autolimbal and allolimbal transplants. Ophthalmology. 2010;117(6):1207-1213.
• Resch MD, Resch BE, Csizmazia E, et al. Permeability of human amniotic membrane to ofloxacin in vitro. Invest Ophthalmol Vis Sci. 2009;51(2):1024-1027.
• Seitz B, Das S, Sauer R, Hofmann-Rummelt C, Beckmann MW, Kruse FE. Simultaneous amniotic membrane patch in high-risk keratoplasty. Cornea. 2011;30(3):269-272.
• Strube YN, Conte F, Faria C, Yiu S, Wright KW. Amniotic membrane transplantation for restrictive strabismus. Ophthalmology. 2011;118(6):1175-1179.

• Amar Agarwal, MS, FRCS, FRCOphth, can be reached at Dr. Agarwal’s Eye Hospital, 19 Cathedral Road, Chennai 600 086, India; fax: 91-44-28115871; email: dragarwal@vsnl.com.
• Thomas John, MD, can be reached at 708-429-2223; fax: 708-429-2226; email: tjcornea@gmail.com.
• Kenneth R. Kenyon, MD, can be reached at Cornea Consultants International or Eye Health Vision Centers, 51 State Road, Dartmouth, MA 02747; 508-994-1400; fax: 508-992-7701; email: kenrkenyon@cs.com.
• Scheffer C.G. Tseng, MD, PhD, can be reached at Ocular Surface Research and Education Foundation, R&D Department, TissueTech, 7000 SW 97th Ave., Suite 213, Miami, FL 33173; 305-274-1299; fax: 305-274-1297; email: stseng@ocularsurface.com.
• Disclosures: Dr. Agarwal and Dr. John have no relevant financial disclosures. Dr. Kenyon is involved with Keera, developer of lyophilized amnion membrane extract. Dr. Tseng is medical director, Ocular Surface Research and Education Foundation Director, R&D Department, TissueTech. He has a financial interest in cryopreserved amniotic membrane and in the ProKera product distributed by Bio-Tissue.