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Keywords:

  • amniotic membrane;
  • equine;
  • cornea;
  • conjunctiva;
  • keratitis;
  • graft

Abstract

  1. Top of page
  2. Abstract
  3. History of amniotic membrane transplantation (AMT)
  4. Scientific basis of clinical application
  5. Indications for AMT
  6. Procurement and surgical techniques
  7. Case series
  8. Materials and methods
  9. Results
  10. Conclusions
  11. References

Amniotic membrane transplantation (AMT) is an effective clinical therapy for reconstruction of the ocular surface in human and veterinary patients. Amnion is avascular and strong, contains antiangiogenic and antiinflammatory properties and growth factors, and has properties that prevent or decrease fibrosis in healing tissue. Indications for its use are steadily growing and include grafting to replace diseased, missing or excised tissue, patching to support diseased tissue during the healing process and as a substrate for the expansion of epithelial cells for transplantation to the cornea. AMT through a combination of mechanical and biologic factors can preserve the integrity of the globe, optimize the visual outcome, and minimize scarring in severely diseased corneas.


History of amniotic membrane transplantation (AMT)

  1. Top of page
  2. Abstract
  3. History of amniotic membrane transplantation (AMT)
  4. Scientific basis of clinical application
  5. Indications for AMT
  6. Procurement and surgical techniques
  7. Case series
  8. Materials and methods
  9. Results
  10. Conclusions
  11. References

The innermost layer of the placenta, the amniotic membrane or amnion consists of a thick basement membrane and an avascular stromal matrix. This relatively acellular material is very strong and has properties that make it uniquely suited to use as a wound patch or graft.1,2 It has a long history of use throughout the body as a wound dressing or surgical patch. It was first used in skin grafting in 1910 and was subsequently found to be useful in the management of burns, the creation of surgical dressings and the reconstruction of, among other things, the oral cavity, bladder, vagina, tympanic membrane and various joints.3 It has been proven to significantly expedite the healing of wounds compared to controls and other dressings. Its first appearance in the literature for ocular use was in 1940 when a description was made of the use of a fresh full-thickness fetal membrane consisting of both amnion and chorion for reconstruction of the conjunctiva defects and repair of symblepharon.3 The success rate in that case series was low, probably due to the inclusion of the chorion. A few years later, in 1946 and 1947, a chemically processed amniotic membrane was employed as a temporary patch for acute ocular burns.4,5 This membrane consisted of amnion alone and was referred to as amnioplastin. It had to be repeatedly applied; however, its use was a remarkable success resulting in shorted hospitalization stays, improved comfort and lessened scarring.4,5 The use of amnion for ophthalmic indications was not pursued further for many years after the advent of amnioplastin and, in fact, no references appear in the literature again until the 1990s.

Amnion was reintroduced for ophthalmic use in 1995 by Kim and Tseng when they described the transplantation of preserved human amniotic membrane for surface reconstruction in severely damaged rabbit corneas.6 In this rabbit model of limbal stem cell deficiency in which the corneas had become conjunctivalized due to the lack of corneal epithelial cell progenitors, the investigators had considerable success reconstructing corneas by replacing the conjunctivalized surface with human amnion.6 This success prompted renewed interest in amniotic membrane for ophthalmic use and since then it has been used for as a therapy for, among other things, corneal burns and ulcerations of many types, corneal and conjunctival reconstruction following the excision of neoplasia and as a carrier for supporting the growth and expansion of epithelial cells.7–21 In recent years, amnion has become the most widely used tissue for ocular surface reconstruction in human ophthalmology.2,22

Scientific basis of clinical application

  1. Top of page
  2. Abstract
  3. History of amniotic membrane transplantation (AMT)
  4. Scientific basis of clinical application
  5. Indications for AMT
  6. Procurement and surgical techniques
  7. Case series
  8. Materials and methods
  9. Results
  10. Conclusions
  11. References

Amniotic membrane transplantation is an effective clinical therapy for ocular surface pathology for many reasons. It has a unique combination of properties, including the ability to facilitate the migration and differentiation of epithelial cells and the reinforcement of cellular adhesion of those same cells, the ability to modulate stromal scarring and the ability to decrease ocular surface inflammation.1,2,22,23 It has also been shown to have anti-angiogenic and anti-microbial effects.22–25

Amniotic membrane consists of three basic layers, an epithelial monolayer, a thick basement membrane and an avascular, hypocellular stromal matrix. The epithelium is usually damaged and nonviable, if not completely denuded, by the preparation, preservation and storage procedures, so is not usually a consideration for therapeutic procedures.22,26

Amniotic basement membrane compositionally resembles that of conjunctiva, making it a nearly ideal material for ocular reconstruction.1 It is a network of reticular fibers that are closely compacted lending it considerable tensile strength. The fact that this basement membrane provides support to the fetus for the length of gestation stands as testimony to its might. It has structural integrity, transparency and elasticity and is known to promote epithelial cell migration, adhesion and differentiation. It has in common with basement membranes of normal cornea and conjunctiva, types IV, V and VII collagen, fibronectin and laminin 1 and 5 which facilitate corneal epithelial cell adhesion and anchorage to stroma.1,7,22 It is a superior substrate for the growth and proliferation of epithelial cells and their progenitors. It allows them to maintain their normal morphology and differentiation, prevents epithelial cell apoptosis, prolongs their lifespan and, in the case of progenitor cells, maintain their clonogenicity.1,23–25 These properties allow that this tissue may be transplanted directly onto recipient corneas to replace limbal stem cell deficiencies, facilitate epithelialization of long-standing ulcerations and repair corneas damaged from a variety of insults.

The stromal side of the membrane consists of a loose matrix of fibroblasts, proteoglycans, glycoproteins and collagen and is rich in fetal hyaluronic acid.1,2,22–25 It has been shown to suppress transforming growth factor-beta (TGF-β) signaling and the proliferation and myofibroblastic differentiation of normal corneal, limbal and conjunctival fibroblasts.1,24,25 This action explains why AMT can reduce scar formation after ocular surface reconstruction and injury. Several growth factors have been identified in the stromal matrix of amnion including hepatocyte growth factor, transforming growth factor, epidermal growth factor and keratocyte growth factor which may contribute to this scar reduction action. Several of these growth factors may also support reepithelialization following AMT.1,24,25 The amnion stromal matrix also has the ability to suppress the expression and activity of certain inflammatory cytokines that originate from the ocular surface epithelia which are often present in abundance on the diseased ocular surface including IL-1α, IL-2, IL-8, interferon λ, tumor necrosis factor-β, TNF-α, basic fibroblast growth factor and platelet derived growth factor.1,2,24,25 This explains some of the anti-inflammatory properties of AMT. The stromal matrix also decreases ocular inflammation by attracting and sequestering inflammatory cells that infiltrate the diseased ocular surface. Those inflammatory cells are inactivated when they are stimulated into rapid apoptosis. The decrease in the presence and activity of inflammatory cells may also be caused by reduced levels of pro-inflammatory cytokines and chemokines and will in turn decrease their further recruitment. Additionally, forms of natural inhibitors of various proteases, inhibitors of metalloproteinases, especially matrix metalloproteinase (MMP)-2 and MMP-9, and nitric oxide synthase and potent anti-inflammatory proteins including IL-10 and IL-1 receptor antagonists have been found in amniotic stroma.1,24,25 Various anti-angiogenic substances have been recognized in amnion as well.26

Corneal neovascularization is a nonspecific response of the cornea to inflammation and may be initiated during various insults and diseases including both infectious and sterile corneal wounds, and immune-mediated reactions. The exact mechanisms of corneal neovascularization have not been fully worked out, but it is understood that migration, proliferation and differentiation of endothelial cells are upregulated by various growth factors that are liberated during inflammation. These same pro-inflammatory chemicals are suppressed in the presence of AMT. This previously described anti-inflammatory action is one way in which amnion decreases corneal neovascularization. Another is via the release of soluble anti-angiogenic factors from the epithelial and mesenchymal cells of amniotic membrane, including interleukin-1 receptor antagonist, all four types of tissue inhibitors of metalloproteinase (TIMP), collagen 18, IL-10, thrombospondin-1, and pigment epithelium-derived factor (PEDF).7,26 These factors decrease vascular endothelial cell proliferation. AMT has been noted to prevent and induce regression of corneal neovascularization in clinical cases.26

There is evidence that amniotic membrane has diverse properties against bacterial and viral infections.7 The fact that the chorioamnion prevents the spread of bacteria from the maternal to the fetal suggests that it may function as a physical barrier against infection. Additionally, various compounds that promote anti-microbial immunity can be induced in amnion, including various interleukins, interferons, TNF-α, activin A, inhibin A, pre-B-cell colony-enhancing factor and leukemia inhibitory factor, particularly amnion that has been exposed to infectious agents, certain cytokines and hormones.7,22–24 Freshly isolated amnion displays constitutive immunity against many viral infections and it contains its own interferon, which differs from IFN-α, β and λ or TNF.7,23 Amnion is also able to store antibiotics and release them over several days.7

Indications for AMT

  1. Top of page
  2. Abstract
  3. History of amniotic membrane transplantation (AMT)
  4. Scientific basis of clinical application
  5. Indications for AMT
  6. Procurement and surgical techniques
  7. Case series
  8. Materials and methods
  9. Results
  10. Conclusions
  11. References

Based on the mechanisms of action and observed clinical effects described above, the use of AMT in ophthalmology is indicated in many situations including as a graft for surface reconstruction of both the conjunctiva and cornea, as a patch for either surface or as a carrier for the growth or expansion of epithelial cells for transplantation.7–23,27 The list of potential indications for AMT in ophthalmology continues to grow (Table 1).

Table 1.   Indications of AMT in human or veterinary ophthalmology
  1. AMT, amniotic membrane transplantation.

Conjunctival surface reconstruction
Ocular surface neoplasia (both)
Pterygium surgery (human)
Chemical burns (both)
Cicatrizing conjunctivitis (both)
Symblepharon release (both)
Fornix formation (human)
Lid reconstruction (both)
Socket reconstruction (human)
Entropion correction (human)
Bleb leakage or revision (human)
Filtering surgery (human)
Corneal surface reconstruction
Ocular surface neoplasia (both)
Persistent epithelial defects (both)
Nonhealing stromal ulcers (both)
Deep stromal ulcers or descemetoceles (both)
Neurotrophic keratopathy and ulceration (human)
Partial or total limbal stem cell deficiency (both)
Bullous keratopathy (both)
Infectious keratitis, viral, bacterial, fungal, parasitic (both)
Preventing scarring following refractive keratectomy (human)
Stevens Johnson syndrome (human)
Melting ulcers (both)
Scleral melt (both)
Band keratopathy (both)
Substrate for expansion of epithelial cells (both)

Because of the therapeutic effects described above, it is reasonable to consider the use of AMT to restore normal stroma and provide a healthy basement membrane for renewed epithelial proliferation and differentiation. In conjunctival reconstruction, AMT may be used as an alternative to conjunctival grafting following removal of large conjunctival lesions such as pteryigium, symblepharon and neoplasms.7–23 It may be used to repair leaking filtration blebs and can be used to line the posterior surface of the eyelids for blepharoplasties and orbit reconstructions.7,27

The anti-inflammatory and anti-angiogenic properties of amnion make it an ideal substance to mitigate the destructive forces at work in instances of keratitis and keratopathy. By decreasing the concentration of inflammatory cytokines, AMT may decrease the severity of corneal melting and corneal neovascularization and improve the likelihood of organic reparation of both epithelial and stromal defects. It can perform protective functions in corneas that have been structurally compromised by disease or keratectomy. By modulating the products of corneal fibroblasts, it can decrease scarring and improve clarity.1,7,24–26 It has been used as a treatment for corneal ulcerations of many types, including those occurring as the result of limbal stem cell deficiencies.8,14 Since the amniotic basement membrane can accommodate proliferating and differentiating epithelial cells, it has been used in human ophthalmology for the production of replacement epithelium and its progenitors ex vivo.7,13,22 The clinical possibilities in this realm have not been explored in veterinary medicine, but hold significant promise. AMT can promote healing of persistent epithelial defects from various etiologies and more structurally compromising ulcers as well.9 This therapy in human ophthalmology is considered superior to the placement of conjunctival grafts and tarsorrhaphy as it provides a more cosmetically acceptable outcome. AMT may be used as a temporary approach to improve patient comfort while awaiting corneal transplantation. In veterinary ophthalmology, it has resulted not only in superior cosmetic outcomes, but has also permitted greater potential for vision compared to the more traditional therapy of conjunctival grafting.

Although there are relatively few reports in the literature regarding the use of AMT for corneal or conjunctival reconstruction in veterinary patients, those that have been published describe positive outcomes similar to those describe in human beings.28–33 In experimentally induced corneal ulcers in dogs, amniotic membrane has resulted in enhanced healing with shorter times to resolution and less scar formation compared to controls and it has been used successfully as a tectonic graft in the repair of full-thickness corneal lesions.31,33 In horses, it has been used with great success in clinical cases of ulcerative keratitis and keratomalacia to preserve globe integrity and a clear visual axis and as an adjunct in the reconstruction of the cornea and conjunctiva following excision of surface neoplasms.28,29 It has also been used sucessfully in clinical cases of keratomalacia, ankyloblepharon and following resection of neoplasia in dogs and cats.32 AMT is a versatile surgical technique in both human and veterinary ophthalmology with a constantly expanding list of potential indications.

Procurement and surgical techniques

  1. Top of page
  2. Abstract
  3. History of amniotic membrane transplantation (AMT)
  4. Scientific basis of clinical application
  5. Indications for AMT
  6. Procurement and surgical techniques
  7. Case series
  8. Materials and methods
  9. Results
  10. Conclusions
  11. References

In human ophthalmology, amniotic membrane is obtained from prospective donors undergoing Caesarean section who are negative for communicable diseases such as HIV, hepatitis and syphilis. This tissue is then processed for storage and maintained in banks. Several protocols exist for processing amnion, but all include washing the placenta with a balanced salt solution and a cocktail of anti-microbial drugs (usually 50 μg/mL penicillin, 50 μg/mL streptomycin, 100 μg/mL neomycin and 2.5 μg/mL amphotericin B) under sterile conditions.7,22 The fetal component of the placenta, which consists of the amnion and the chorion, forms the limits of the sac that encloses the fetus with the amnion forming the innermost layer of the sac.1 The amniotic epithelial monolayer is adjacent to the fetus while the spongy stromal matrix sits adjacent to the chorion. The amnion is separated from the chorion by blunt dissection, which is usually relatively easy since the amniotic stroma is only loosely connected to the chorion.1 The amnion is recognized as the avascular portion. It is then cut to a manageable size and placed epithelial side up on nitrocellulose paper. The amnion may then be placed in media, usually a mixture of glycerol and Dulbecco Eagle's Medium, and frozen at −80º until further use. Amnion may also be freeze-dried or lyophilized for storage.7,22

The most frequent use of AMT in veterinary ophthalmology to date has been in the equine eye due to the relative ease of procuring and handling equine amnion compared to that of small animals and the severity of the corneal disease experienced by horses.28,29 However, equine amnion has also been used successfully in corneal and conjunctival reconstruction in small animal patients.30–33 We have had success using the guidelines concerning procurement and processing of tissue reported by the Food and Drug Administration for our equine placentas.6,7,28,29 Although we do not screen donor mares for specific diseases or infections, we take care to use amnion harvested aseptically from healthy placentas from healthy mares with no known history of transmissible disease. The case series below will describe the use and outcomes of AMT in 58 clinical equine cases.

There are three basic principles for the application of AMT upon which the surgical technique chosen for an individual case is based.7,22

Inlay or graft technique

In this procedure, the amnion is tailored to the size of the defect and is meant to act as a scaffold for epithelial cell migration. This graft then becomes integrated into the host tissue. The amnion is secured with its basement membrane up to allow migration of surrounding epithelial cells onto the membrane (Fig. 1).

image

Figure 1.  The use of AMT for a melting corneal ulcer in a horse. (a) Melting corneal stromal ulcer at presentation. (b) Immediate post-operative photograph of the eye in Figure 1a with a double application of amniotic membrane. The first layer covers the corneal wound in an inlay or graft fashion, while the outer layer has been applied as an overlay or patch. (c) One month after AMT surgery. Once this vascular granulation tissue clears, the scar that remains is mild.

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Overlay or patch technique

The patch technique utilizes amnion as a sort of biologic contact-lens in order to protect the healing surface of the defect below it. The patch may also reduce inflammation by its barrier effect against the chemical mediators in the tear fluid. When used as a patch, the amnion is either secured to the cornea with its basement membrane side up and it either falls off or is removed or it may be secured with the basement membrane side down which presents adhesion and incorporation of the patch (Fig. 2).

image

Figure 2.  AMT may be used as an adjunct to corneal transplantation. (a) This malacic cornea had perforated necessitating surgical stabilization. (b) This is an immediate post-operative photograph of the eye from (a), which had undergone penetrating keratoplasty with an overlay patch of amniotic membrane. (c) The appearance of the eye 1 month after AMT. Moderate scarring is present, but still actively remodeling.

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Filling-in or layering technique

Multiple pieces on amnion trimmed to the size of the defect are placed within the depth of the ulcer crater. A larger graft is secured to the edges of thee defect in and inlay fashion. An additional and larger patch may be placed atop the graft to help preserve the deeper layers for a longer duration.

In preparation for surgical placement of amniotic membrane, the eye should be prepped routinely with an anti-microbial wash, usually dilute betadine, and a topical anesthetic agent. Loose epithelium surrounding an epithelial or stromal defect or over an area of bullous keratopathy should be debrided with forceps, microsurgical sponges and a microsurgical blade. Any diseased or fibrotic conjunctiva or cornea should be completely resected prior to placement of the graft or patch. Once the wound or defect is adequately prepared, the amnion should be trimmed to the desired size and oriented atop the lesion. It can be difficult to orient the amnion if it comes off of its nitrocellulose sheet. The stromal surface can be identified by the presence of vitreous-like strands that can be raised by a sponge.

In human ophthalmology, 10–0 nylon or another small gauge nonabsorbable suture material is used to anchor the amniotic membrane to the globe.2,22,23 Typically, simple interrupted or continuous sutures will be used on any graft-type applications. Most grafts are fashioned so that the graft is 1 mm larger than the defect to which it is to be applied. Patch applications usually involve even larger pieces of amnion and are usually sutured to the limbus, again with 10–0 nylon or its equivalent. Conjunctival lesions are given to rapid healing, therefore, 8–0, 9–0, or 10–0 Vicryl, an absorbable suture material, is used to affix the amnion to the lesion. Conjunctival lesions involving the fornix will require a larger suture for fixation, something on the order of 4–0 or 5–0 Vicryl or chromic gut.22 In most of our equine cases, the amniotic membrane was affixed to the corneal or conjunctiva with either 7–0 or 8–0 Vicryl in a simple interrupted or continuous pattern. A smaller gauge needle and absorbable suture (8–0 or 9–0 Vicryl) would be appropriate for the use of AMT in small animals. Sutureless techniques are in constant development in attempt to improve the ease of application, decrease the time required for application and anesthesia if it is indicated, and to improve patient comfort. Fibrin glues are in development and have shown significant promise in the arena of human ophthalmology. Their great cost at present is a contraindication to their use in veterinary ophthalmology. We have had some success with using minute quantities of surgical tissue glue to apply amniotic membrane and synthetic corneal replacement material in our veterinary patients.

Post-operative care for both human and veterinary cases consists of continued medical therapy for the primary disease process and topical anti-microbial therapy until the epithelium has healed. Most human patients receive bandage contact lenses to improve retention of the membranes and improve post-operative comfort.7 Topical prednisolone is usually used as well in human ophthalmology.22,23 Its use would be concerning and perhaps even contraindicated in many veterinary cases. Post-operative monitoring in either human or veterinary cases can continue as it would prior to the application of amnion with slit-lamp examination, although the cornea may be difficult to appreciate through the initially opaque membrane.

The most common and serious complications of AMT are the spread of an underlying infection to adjacent cornea or the anterior chamber in cases of infectious keratitis and the failure of the AMT to be retained.2,7,22,23 In cases of extensive ocular disease, the membrane may either dissolve or be sloughed, necessitating its replacement.2,4,5,7,22 Post-operative infections in initially sterile cases receiving AMT in humans is relatively low at 1.6%.7 Calcification of the AMT in humans occurs in 12.8% of cases, but has not been recognized to date in our veterinary cases.7 In equine ophthalmology, progression of the primary corneal disease despite the AMT is the most concerning and common complication. In contrast to the placement of a conjunctival graft, there is no stabilizing vascular supply transplanted to the site of disease. Therefore, the immediate post-operative period in AMT is delicate as the disease for which therapy is indicated is often quite severe. Frequent and thorough post-operative follow-up is recommended. In equine ophthalmology, AMT offers the advantage of a potentially much less dense and sight-limiting scar over the traditional therapy of a conjunctival graft.

Processed amnion is commercially available for human ophthalmology and amnion extracts and amnion tissue within contact-lens conformers are being used in human patients and may be a reasonable goal for veterinary applications in the future.

Case series

  1. Top of page
  2. Abstract
  3. History of amniotic membrane transplantation (AMT)
  4. Scientific basis of clinical application
  5. Indications for AMT
  6. Procurement and surgical techniques
  7. Case series
  8. Materials and methods
  9. Results
  10. Conclusions
  11. References

Corneal disease is the most frequent presenting complaint for equine patients presenting to the ophthalmology department at the Veterinary Medical Center of the University of Florida. Over the last few years, we have been utilizing AMT as a therapy for severe keratopathy in our equine patients. The following is a description of the equine cases we have to date with follow-up greater than 6 months, the indication for which AMT was performed, and the cosmetic and visual outcomes thereafter.

Materials and methods

  1. Top of page
  2. Abstract
  3. History of amniotic membrane transplantation (AMT)
  4. Scientific basis of clinical application
  5. Indications for AMT
  6. Procurement and surgical techniques
  7. Case series
  8. Materials and methods
  9. Results
  10. Conclusions
  11. References

A retrospective study of 58 equine cases that presented to the University of Florida Veterinary Medical Center with severe keratopathy which were treated with AMT in addition to medical therapy was performed. Medical records were reviewed and data regarding signalment, indication for surgery, visual outcome and cosmetic outcome were recorded.

Visual status was determined at the final post-operative examination in all cases and was characterized by the presence or absence of a menace response, ability to track an object or subject on the side of the affected globe and the subjective behavioral responses observed by the owner. Cosmetic outcome was determined by subjective assessment of the percentage of corneal surface area with significant residual scarring, fibrosis, vascularization and pigmentation. Corneal scarring was classified as mild, moderate or severe. Mild scarring was determined to be less than one-third of the total surface area of the cornea and was faint with minimal fibrosis, ghost vessels and little to no pigmentation and was judged to cause minimal to no visual deficits (Fig. 3). Moderate scarring was one-third to one-half of the entire surface area of the cornea with some fibrosis, neovascularization and pigmentation of less than half of the scarred area (Fig. 4). Moderate scarring was noticeable to the casual observer, but did not impair functional vision. Severe corneal scarring affected the majority of the cornea and was observed to severely limit or prohibit vision entirely. Globes that became phthisical or were enucleated were included in the severe category.

image

Figure 3.  AMT may be used to stabilize melting ulcers of extreme size. (a) Complete melting ulcer in a foal. The entire cornea was affected. (b) This is the eye 18 months after surgical placement of amniotic membrane as a patch. Mild scarring remains.

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image

Figure 4.  AMT provides physical and biochemical support for the cornea. (a) The ulcer on this foal’s eye was large, encompassing the majority of the cornea and was bulging ominously. (b) This is the eye 3 weeks after AMT for treatment of its melting corneal ulcer.

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Results

  1. Top of page
  2. Abstract
  3. History of amniotic membrane transplantation (AMT)
  4. Scientific basis of clinical application
  5. Indications for AMT
  6. Procurement and surgical techniques
  7. Case series
  8. Materials and methods
  9. Results
  10. Conclusions
  11. References

Fifty-eight cases were identified that had received AMT for some sort of globe or sight threatening keratopathy. Thirty cases were female and 28 were male, neuter status undetermined. Nine breeds were represented including thoroughbred, Quarter Horse, warmblood, Standardbred, Welsh Pony, Tennessee Walking Horse, Arabian, American Paint Horse and Belgian Draft. The ages ranged from 1 month to 22 years of age with a median of 6.7 years.

Of these 58 cases, 31 were treated for melting ulcers or bullous keratopathy, 13 had AMT performed in conjunction with penetrating keratoplasty, 12 received AMT following keratectomy for a superficial neoplasm and 2 received AMT following keratectomy for biopsy and treatment of an immune-mediated keratitis (Figs. 5 and 6). Pre- and post-operative medical therapy for all cases consisted of the systemic nonsteroidal anti-inflammatory medication flunixin meglumine, topical atropine, topical autologous serum and topical antibiotics and anti-fungal agents. The dosage and frequency of these medications varied with the severity of the disease process and the response to therapy.

image

Figure 5.  Amnion not only has anti-inflammatory properties, it also has some anti-microbial properties. (a) This infected corneal stromal ulcer was accompanied by severe uveitis. (b) Six weeks after AMT, the ulcer had healed and the cornea was remodeling.

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image

Figure 6.  Scarring following keratectomy for surface neoplasma can be reduced with the use of AMT. (a) The appearance of a corneal squamous cell carcinoma prior to resection. (b) The immediate post-operative appearance of the eye following keratectomy and placement of amniotic membrane in an inlay or graft fashion. (c) Three months after AMT following keratectomy for a corneal neoplasm, the amniotic membrane has been incorporated into the host’s cornea and scarring is minimal.

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At the final post-operative examination, visual status was assessed and 53 affected eyes were determined to be sighted. The five eyes that were not sighted had either severe corneal scarring preventing vision, had secondary intraocular damage resulting in phthisis bulbi with cataract formation and extensive posterior synechia or were enucleated because of endophthalmitis.

The extent of corneal scarring was used to determine the cosmetic outcome. Mild corneal scarring was present in 40 eyes (69%), all of which were deemed to have excellent cosmesis, barely noticeable to the casual observer. Moderate corneal scarring was present in 14 eyes (24%), all of which were characterized as having acceptable cosmesis. Unacceptable cosmesis occurred in four eyes (7.0%), one of which had extensive corneal scarring that prevented sight, two of which became phthisical and one of which was enucleated secondary to endophthalmitis. The eyes that were ultimately characterized with moderate or severe scarring were the most severely affected by primary disease (Fig. 7).

image

Figure 7.  AMT can be useful in potentially catastrophic cases of corneal disease that would be rendered non-visual by conjunctival grafting. (a) This case of fungal keratitis required surgical stabilization with penetrating keratoplasty and a corneal transplant. AMT was performed following replacement of the diseased cornea as a patch. (b) The eye 1 month after penetrating keratoplasty and AMT. Corneal scarring is significant, but would continue to diminish with time. The eye was sighted following resolution.

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Conclusions

  1. Top of page
  2. Abstract
  3. History of amniotic membrane transplantation (AMT)
  4. Scientific basis of clinical application
  5. Indications for AMT
  6. Procurement and surgical techniques
  7. Case series
  8. Materials and methods
  9. Results
  10. Conclusions
  11. References

The utility of AMT in the healing of ocular surface defects is undeniable. Its uses and indications are constantly evolving and expanding in both the human and veterinary ophthalmology arenas. In many cases such as the more severely affected described above, the traditional therapy of placing a conjunctival graft upon a corneal wound or defect would render a sighted or a potentially sighted globe blind. AMT should be considered as a treatment option in cases that require ocular surface reconstruction for the treatment of corneal and conjunctival defects both organic and surgically induced.

References

  1. Top of page
  2. Abstract
  3. History of amniotic membrane transplantation (AMT)
  4. Scientific basis of clinical application
  5. Indications for AMT
  6. Procurement and surgical techniques
  7. Case series
  8. Materials and methods
  9. Results
  10. Conclusions
  11. References
  • 1
    Niknejad H, Peirovi H, Jorjani M et al. Properties of amniotic membrane for potential use in tissue engineering. European Cells and Materials 2008; 15: 8899.
  • 2
    Dua HS, Azuara-Blanco A. Amniotic membrane transplantation. British Journal of Ophthalmology 1999; 83: 748752.
  • 3
    Trelford JD, Trelford-Sauder M. The amnion in surgery, past and present. American Journal of Obstetrics and Gynecology 1979; 134: 833845.
  • 4
    Sorsby A, Sorsby HM. Amniotic membrane grafts in caustic burns of the eye. British Journal of Ophthalmology 1946; 30: 337345.
  • 5
    Sorsby A, Haythorne J, Reed H. Further experience with amniotic membrane grafts in caustic burns of the eye. British Journal of Ophthalmology 1947; 31: 409418.
  • 6
    Kim JC, Tseng SCG. Transplantation of preserved human amniotic membrane for surface reconstruction in severely damaged rabbit corneas. Cornea 1995; 14: 473484.
  • 7
    Heiligenhaus A, Heinz C, Schmidz K et al. Amniotic membrane transplantation for the treatment for corneal ulceration in infectious keratitis. In: Essentials in Ophthalmology Corneal and External Eye Disease. (eds ReinhardT, LarkinF) Springer Berlin Heidkeberg, New York, 2007; 1536.
  • 8
    Tseng SCG, Prabhasawat P, Barton K et al. Amniotic membrane transplantation with or without limbal allografts for corneal surface reconstruction in patients with limbal stem cell deficiency. Archives of Ophthalmology 1998; 116: 431441.
  • 9
    Lee SH, Tseng SCG. Amniotic membrane transplantation for persistent epithelial defects with ulceration. Archives of Ophthalmology 1997; 123: 303312.
  • 10
    Kruse FE, Rohrschneider K, Volcker HE. Multilayer amniotic membrane transplantation for reconstruction of deep corneal ulcers. Ophthalmology 1999; 106: 15041511.
  • 11
    Chen HJ, Pires RTF, Tseng SCG. Amniotic membrane transplantation for severe neurotrophic corneal ulcers. British Journal of Ophthalmology 2000; 84: 826833.
  • 12
    Meller D, Tseng SCG. Conjunctival epithelial cell differentiation on amniotic membrane. Investigative Ophthalmology and Visual Science 1999; 40: 878886.
  • 13
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