What is the amniotic membrane?
The amniotic membrane is a semi-transparent avascular tissue that comes from the placenta. It is isolated under strictly sterile conditions after labour and it is processed in a health authority-approved tissue bank.
It may take the format of a cryopreserved coating that can be implanted in the eye after defrosting, or a freeze-dried powder which, after being prepared in sterile conditions, can be used as eyedrops. It can also take the format of a freeze-dried coating for direct implantation in the eye.
The amniotic tissue is ideal as a frame for epithelial growth. It is known to have antiangiogenic, anti-inflammatory and antibacterial properties. It helps to heal wounds. El tejido amniótico es ideal como armazón para el crecimiento epitelial.
The amniotic membrane is also used in laboratories to cultivate cells, like scaffolfing in tissue engineering.
What are the indications for this surgical procedure?
An amniotic membrane transplant is indicated in emergency cases of severe chemical burn and cases of acute Stevens-Johnson syndrome, when there is an imminent perforation of the eye.
It is also indicated as a substitute for conjunctival tissue after resection of a large pterygion, in cases of recurring pterygion where there isn't enough healthy conjunctiva to use as an autograft.
It can also be used in cases of ocular surface tumours to cover the open area. It can also be used to correct eyelid abnormalities, like in cases of previous chemical burns, cicatricial pemphigoid and Stevens-Johnson syndrome.
It can be implanted in the cornea in cases of persistent epithelial defects, bullous keratopathy, calcific band keratopathy, profound corneal ulcers and small corneal perforations.
How is the procedure performed?
Under sterile conditions, after defrosting the cryopreserved amniotic sac, the surgeon measures the size of the defect to cover, cuts and adapts the membrane to the right size, then places it on top of the conjunctival or corneal tissue.
It can be applied with very fine sutures or with tissue adhesive. The surgeon may use one or various layers of the membrane, depending on the thickness required for each case.
Results
The cosmetic results are excellent since it combines with the colour of conjunctiva which is semi-transparent. After a few weeks, the membrane reabsorbs and is covered by the patient's own epithelium.
Possible risks
Like in any other case of ocular surface surgery, one of the risks is infection. Other risks include the implant sliding down, complete reabsorption of the amniotic membrane, the non-healing of the ulcer and recurrence of the disease, especially in chronic cases like herpetic keratitis, neurotrophic ulcers, Stevens-Johnson syndrom, cicatricial pemphigoid or Sjogren's syndrome.