Healthcare and Medicine Reference
In-Depth Information
In ophthalmology, AM has been used as a graft to replace the damage
stromal matrix with its epithelium up when it is expected to become covered
by host conjunctival or corneal epithelium; as a patch with its epithelium
down, which facilitates trapping of infl ammatory cells in the stroma,
reducing infl ammation; and in a combination of both.
Mechanism of action. The underlying physiologic mechanisms through which
AM confers benefi cial effects on the reconstruction of the ocular surface
have not been completely elucidated yet ( Table 2 ).
Table 2 This table summarizes the principal mechanisms of action of amniotic membrane
(AM).
Mechanisms of Action of Amniotic Membrane
Prolongs life span and maintains clonogenicity of epithelial progenitor cells.
AM expresses epidermal growth factor, nerve growth factor, hepatocyte growth factor,
and keratinocyte growth factor.
Facilitates the migration of epithelial cells, reinforces the adhesion of the basal epithelium,
promotes cellular differentiation, and prevents cellular apoptosis.
Promotes goblet cell differentiation when combined with conjunctival fi broblasts.
Inhibitory effects on various proteases, including decreased expression of MMP-1 and 2.
Decreases expression of IL-1, IL-2, IFN-γ and TNF-α.
Suppresses TGF-D signalling system and myofi broblast differentiation of normal
fi broblasts.
Decreases expression of VEGF.
MMP: matrix metalloproteinase. VEGF: vascular endothelial growth factor. TNF: tumour
necrosis factor. IFN: interferon.
Evidence indicates that AM modulates the level of various cytokines,
growth factors, enzymes, and receptors (Li et al. 2005). The three main
favourable properties of the AM are anti-infl ammatory, antiangiogenic and
antiscarring effects.
Clinical indications of AM . The clinical indications of conjunctival and corneal
diseases are summarized in Table 3.
Amniotic membrane as a graft for conjunctival surface reconstruction. Amniotic
membrane transplantation can be used to reconstruct the conjunctival
surface as an alternative to conjunctival graft after removal of large lesions
and to restore normal stroma and provide a healthy basement membrane
to promote epithelial proliferation and differentiation (Tseng et al. 1997).
Amniotic membrane transplantation as a graft for corneal surface reconstruction.
Studies on the effi cacy of AM to provide tectonic support in impending or
recent corneal perforation have yielded different and controversial results.
However, it is an excellent method when a corneal graft is not available
or in some perforations, especially those related to vasculitic peripheral
 
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