SAEVA Congress 2018 Proceedings | 12-15 February 2018 | ATKV Goudini Spa
• Anti-scarring [ antifibrotic ]
• Anti-angiogenesis [ anti blood vessel proliferation which leads to scarring ] Endostatin , Thrombospondin-1 , TIMPs .
• Promotes epithelialisation - bFGF , HGF , EGF , NGF
• Reduction of patient pain
• Controlling apoptosis [ death ] of corneal epithelium cells .
• Anti-bacterial - bactericidin , b lysin , lysozyme , transferrin , lactoferrin .
Human amnion grafts are used regularly as a treatment option in medical ophthalmology and have been used very successfully in animal studies without observing any adverse effects of cross immunity challenges . It is believed , and has been shown for a number of species , that the similar advantages above will be achieved when using a cryopreserved amnion graft across the species barrier . The author has used equine amnion on cats and dogs with excellent results and human amnion on cats and dogs . Bovine cryopreserved amniotic membrane applied to dogs ’ corneal ulcers has shown to have statistically significant improved rates of healing when compared to normally treated dogs , those having a third eyelid flap and those receiving a contact lens as treatment options . It also appears that fetal tissues such as the amnion have very low immunity stimulation when placed on donor tissues or even incorporated into donor corneas .
The amnion graft tissue has two main components or layers of cells . It is the basement membrane of the amnion that promotes epithelial growth and differentiation , re-enforces the adhesion of basal epithelial cells and prevents epithelial cell death . The stromal matrix however suppresses TGF-β [ transforming growth factor ] signalling and the proliferation and myofibroblastic differentiation of normal corneal and limbal fibroblasts , thereby inhibiting the unwanted production of extracellular matrix and scarring of the cornea which can inhibit vision . This is a very important advantage compared to a conjunctival graft which would leave a serious scar on the cornea for life . Because amnion tissue reduces the concentration of inflammatory cytokines , it appears to reduce the severity of corneal melting , neovascularisation and improve the repairing ability of both epithelial and stromal defects .
A number of different graft techniques are available when using amnion . The most common is the “ inlay ” technique where the corneal bed is surgically trimmed and a piece of amnion is tailored to the size of the defect and sutured with its stromal side down with 7 / 0 vicryl sutures . This results in the amnion being incorporated within the host tissue as the upper basement membrane encourages migration of epithelial cells onto and over the membrane resulting in the amnion being incorporated into the host tissue .
The second option is an “ overlay ” or patch technique where the amnion is placed like a contact lens over the defect to be either left or removed later or if the amnion is secured with its basement membrane down it will prevent adhesion and incorporation into the defect . The host epithelium then grows under the amniotic membrane . The amnion either dissolves or can be removed later . Amnion can also be used in a stacked manner where sequential pieces are placed into the stromal defect and then covered by a larger piece .
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