21/09/14
  
Amniotic Membrane Transplantation
Miércoles, 17 de Junio de 2009 00:00

Amniotic membrane transplantation (AMT) was first used by Kim and Tseng for corneal surface reconstruction in a rabbit model of total limbal deficiency.
Tsubota et al later described the use of amniotic membrane with limbal allograft transplantation in patients with ocular cicatricial pemphigoid and Stevens-Johnson Syndrome.

Amniotic membrane grafts have also been used as an alternative to conjunctival flaps in treating persistent and refractory corneal epithelial defects and ulceration. The procedure has been used to create a limbal barrier in pterygium surgery and for conjunctival surface reconstruction following excision of tumors, scars and symblepharon.

The amniotic membrane is a thick basement membrane and avascular stromal matrix.  Lee and Tseng theorize that these features are crucial to successful transplantation.  The basement membrane facilitates migration of epithelial cells, reinforces adhesion of basal epithelial cells and promotes epithelial differentiation.  The basement membrane is also important to prevent apoptosis. As only the substrate without cells is employed, there is no adverse reaction of rejection.

Human amniotic membrane is prepared and preserved according to the method originally described by Lee and Tseng and by Tseng and Prabhasawat et al.

  1. Human placenta is obtained shortly after an elective cesarean section delivery from an individual pre screened for HIV, hepatitis, and syphillis. 
  2. The Placenta is cleaned of blood and washed with sterile phosphate buffered saline solution containing penicillin G 50 mg/ ml, streptomycin 50 mg/ml, neomycin 100 mg/ml and amphotericin B 2.5 mg/ml.
  3. The amnion is separated from the rest of the chorion by blunt dissection and flattened onto a nitro-cellulose paper with the epithelial basement membrane surface facing away from the paper.
  4. The paper with adherent amniotic membrane is then cut into 3x4 cm sheets and stored before transplantation at -800C in a sterile vial containing Dulbecco modified Eagle medium and glycol at a ratio of 1:1 (vol./vol.).
  5. The recipient eye is prepared the same way as for other surface reconstruction procedure that is peritomy, excision of perilimbal conjunctiva for 5-7 mm and superficial keratectomy. Preserved amniotic membrane is transferred to cover the recipient eye surface defect with the basement side surface facing up. The membrane is anchored to the surrounding tissues with 10-0 nylon sutures. It is then covered by a bandage contact lens.

In a study employing amniotic membrane with and without limbal allograft transplants and penetrating keratoplasty, Tseng et al demonstrated that in eyes with chemical burns (n=14); Stevens Johnson Syndrome, toxic epidermal necrolysis or pseudopemphigoid (n=5); contact lens induced keratopathy (n=3); aniridia (n=3); multiple surgical procedures (n=2); atopy (n=2); and unknown cause (n=2), all amniotic membrane covered eyes (except for two eyes with atopy) showed rapid epithelialisation (2-4 weeks) and reduced inflammation, vascularization and scarring.

For the mean follow up of 15.4 months, 25 of 30 eyes showed visual improvement ranging from 1 to 6 lines. Corneal graft rejection occurred in 9 of 14 eyes and reversible early limbal allograft rejection in 3 of 21 eyes. They concluded that AMT alone is sufficient for partial limbal deficiency with superficial involvement and is superior to allo-limbal transplantation (ALT) since it is not necessary to administer cyclosporine. ALT, however, is needed for total limbal deficiency, and AMT in this situation helps reconstruct the perilimbal stroma with reduced inflammation and vascularisation.

Lee and Tseng performed AMT in 11 eyes for persistent epithelial defects with ulceration and obtained successful reepithelialization in 10 of 11 eyes. One patient's wound failed to heal because of preexisting corneal perforation pursuant to severe rheumatoid arthritis.

The judicious evaluation and management of ocular surface disorders is a challenging task. Currently available therapeutic options are able to rehabilitate the ocular surface in a reasonably large proportion of eyes. Ongoing research into the regulatory mechanism of limbal stem cells may open up exciting frontiers leading to an enhancement of our therapeutic armamentarium in successfully managing these disorders.

Good night,

LL
Luis W. Lu, MD, FACS
Director, Elk County Eye Clinic
Senior Staff Member, Pennsylvania Eye Consultants
www.elkcountyeyeclinic.com