amniotic membrane, or amnion, comprises the innermost layer of the placenta.
Amniotic membrane transplantation (AMT) has been used in many different
types of reconstructive surgery1. Davis in 1910 reported the
use of fetal membranes as a skin substitute. AMT became important because
of its ability to diminish the occurrence of adhesions and scarring, its
ability to enhance wound healing and epithelialisation, and its antimicrobial
potential. In particular, the amniotic membrane expresses incomplete HLA-A,
B, C, and DR antigens 2, which may account for the fact that
immunological rejection after transplantation has not been observed.
1940, De Roth used a fresh fetal membrane (ie both amnion and chorion)
as a graft for conjunctival surface reconstruction with limited success
Sorsby et al 4,5 in 1946 and 1947 reported the successful use
of amniotic membrane as a patch graft in the treatment of acute ocular
burns. Interest in AMT then waned and it was not until Kim and Tseng 6
successfully reintroduced the concept, that interest in AMT was revived.
amniotic membrane consists of a single layer of cuboidal epithelial cells,
a thick basement membrane and an avascular stromal matrix, loosely attached
to the chorion.
placenta provides amniotic membrane for ophthalmic use - sufficient for
20-30 transplants. In addition, amniotic membrane is easily stored (so
that there is an abundant supply). In the United Kingdom in 1997, a human
amniotic membrane bank, based at The North London Tissue Bank, was established
for provision of amniotic membrane in ophthalmic surgery. This was followed
in 1999 by the formation of AMT users group (AMTUG) to establish clinical
and research collaboration and guidelines for fire procurement, processing
and distribution of amniotic membrane. East Grinstead and Nottingham also
established (1996) amniotic membrane banks for local use.
membrane is harvested from consenting seronegative (hepatitis B and C virus,
syphilis and human immunodeficiencv virus) maternal donors during elective
caesarian section. Under sterile conditions, the placental membrane is
washed in a balanced salt solution (BSS) to remove clots and debris. The
membrane is then bathed in a cocktail of antimicrobial medium for 24 hours,
followed by a second wash in BSS. Subsequently, the amnion is separated
from the chorion and divided into pieces measuring approximately 2cm2 and
mounted, stromal side down, onto nitrocellulose cards. The membrane is
then placed in a plastic container, and stored in 50% glycerol at -80°C
for up to 2 years. Serological tests are repeated on the maternal donor
six months after delivery before its release for clinical use.
Clinical Effects and Mechanisms of Action
membrane has been found to:
of cytokines, growth factors and protease inhibitors, such as IL-4, 6 and
IO; EGF, FGF, TGF, HGF, and 2-macrobulin, have been found in cryopreserved
amniotic membranes. The presence, concentration and action of these substances
may account for most of the observed clinical effects and its mechanisms
(7) of action such as:
a normal epithelial phenotype
the adhesion of tissues
Use In Ophthalmology
of inflammatory cells with anti-protease activities
of TGF-signalling system and myofibroblast differentiation of normal fibroblasts
of the life span and clonogenicity of epithelial progenitor cells
of non-goblet cells epithelial differentiation
of goblet cell differentiation when combined with conjunctival fibroblast
membrane can be used in a number of indications, either as a 'substrate'
to replace the damaged ocular tissue or as a 'patch' (biological dressing),
or a combination of both as summarised below:
stem cell deficiency (partial or total): combined with stem cell graft
bleb leakage or revision
the time of surgery, the container with amniotic membrane is thawed at
room temperature just before its use, and the membrane is rinsed three
times in BSS. The membrane is then gently separated from the nitrocellulose
paper with blunt forceps.
is not performed in a universal manner. There have been contradictory reports
concerning the right way to place the amnion on the ocular surface. The
membrane can be sutured to the ocular surface with its epithelium-basement
membrane side up and the stromal side in contact with the eye (preferred
technique) or stromal side up, away from the eye. The stromal side of the
membrane is sticky, similar to vitreous and the epithelial basement membrane
side is shiny and non-sticky.
amniotic membrane is then gently spread on to the ocular surface and trimmed
to the appropriate shape and size (See photo). In cases of corneal pathologies
(eg persistent epithelial defect) the membrane is secured in place using
10-0 nylon interrupted sutures to the cornea. There is a consensus that
in corneal/limbal diseases (eg chemical injury) a membrane much larger
than the affected area is needed. In these cases, a combination of intercepted
10-0 nylon sutures to the conjunctiva/episclera and a 11-0 nylon continuous
suture (ie purse string bedding suture just outside the limbus) is usually
required, although 10-0 Vicryl suture can also be used. In conjunctival
surgery the amnion is used as a substrate to cover the defect after removal
of the affected tissue. In those circumstances where reconstruction of
the conjunctival fornices is needed, a spacer (eg retinal band) is used
to maintain the fornices until epithelialization has occurred. Amniotic
membrane becomes indistinguishable from conjunctival tissue once covered
by the epithelium.
therapeutic contact lens is routinely used, at the end of the operation,
to protect and keep the amniotic membrane in place and also for comfort.
Occasionally, a tarsorrhaphy may also offer additional protection. The
sutures and contact lens are often removed after 2 to 4 weeks. Recommended
post-operative topical treatment consists of preservative free antibiotic
and corticosteroid drops.
addition to the above surgical techniques, there has been an increasing
interest in the experimental transplantation of tissue-cultured limbal
stem cells and amniotic membrane onto the cornea for treatment of ocular
surface pathologies. Studies in animals and human beings have provided
experimental evidence to support this theoretical approach. 9,10
membrane, when used as a biological dressing (eg chemical injury), usually
disintegrates within 2 to 4 weeks after the operation. The membrane will
however, become incorporated in the ocular tissue when used as a substrate
replacement (eg corneal ulceration, pterygium surgery, symblepharon lysis
and conjunctival surface reconstruction).
has been successfully used in ophthalmic surgery, but not without complications.
Post-operative infection, although rare, is one of the risks associated
with this procedure. The amnion cm also become loose or dislocated as a
result of loose/broken sutures. Haemorrhage under the membrane and early
disintegration of the membrane have also been observed. Lack of its beneficial
effect may also occur possibly related to problems with processing.
membrane has been successfully used in a number of procedures for restoration
of the ocular surface. As its mechanism of action becomes more fully understood,
its application will become more refined, with more appropriate usage of
this valuable technique. The full potential of this technique is not known,
thus randomised prospective studies are needed.
C. Figueiredo, on behalf of AMTUG
Victoria Infirmary Newcastle upon Tyne
JD, Trelford-Sauder M. The amnion in surgery, past and present. Am J
Obstet Gynecol 1979;134:833-845.
CA, Adinolfi M, Welsh KI, Leibowitz S, McColl 1. Immunogenicity of human
amniotic epithelial cell after transplantation into volunteers, Lancet
Roth A. Plastic repair of conjunctival defects with fetal membrane. Arch
A, Symons HM. Amniotic membrane grafts in caustic burns of the eye. Br
J Ophthalmol 1946;30:337-45.
A, Haythorne J, Reed H. Further experience with amniotic membrane grafts
in caustic burns of the eye. Br J Ophthalmol 1947,31:409-18.
JCI, Tseng SCG. Transplantation of preserved human amniotic membrane for
surface reconstruction in severely damaged rabbit corneas. Cornea
SCG, Tsubota K. Amniotic Membrane Transplantation for Ocular Surface Reconstruction.
In: Ocular Surface Diseases: Medical and Surgical Management Ed.
Holland EJ and Mannis MJ, Sringer, in press, 2001.
D, Pires RTF, Mack RJS, Figueiredo FC et al, Amniotic membrane transplantation
for acute chemical or thermal burns. Ophthalmology 2000, 107:980
N. Inatomi, Quantock AJ et al. Amniotic membrane as a substrate for cultivating
limbal epithelial cells for autologous transplantation in rabbits, Cornea
2000; 19:65 71.
RJF, Li L-M, Chen I-K. Reconstruction of damaged corneas by transplantation
of autologous limbal epithelial cells. N Eng J Med 2000;343:86 93.
J Ophthalmol 1947;31:409-18.
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