Physicians placed the first fetal membrane on the eye over 70 years ago but poor outcomes, likely due to inefficient processing of the membrane, resulted in limited utilization until 1995. In the past 20 years, the use of amniotic membranes for conjunctival and cornea diseases has grown significantly.
The amniotic membrane is made up of a single-layer of epithelium, a thick basement membrane and an avascular connective tissue matrix. The membrane is a unique material containing various collagen types, extracellular matrix, specialized proteins, and healing growth factors. Amniotic tissue has little or no HLA-A, B and C antigens and therefore imparts low immunogenicity.
Consenting women donate the amniotic membrane when they deliver birth via Cesarean section. Donors are screened following FDA regulations and American Association of Tissue Banks standards. Clinicians test donor blood specimens for infectious diseases.
When placed on the eye, the amniotic membrane can act as a scaffolding for cell growth and promotes wound healing while exhibiting anti-inflammatory, anti-angiogenic, anti-fibrotic and anti-microbial benefits.
Although the membranes are effective, they have traditionally been limited to use in the operating room where the membrane was either sutured in place or applied with a bioadhesive. Recent advances have given clinicians two types of amniotic membranes that are commercially available for in-office use.
Cryopreserved sutureless amniotic membranes undergo a slow freezing process to -80º C using a preservation medium. The slow freeze is important to prevent ice formation on the membrane. This technique preserves many of the cellular components. The membrane is stored frozen and then brought to room temperature at the time of use.
ProKera (BioTissue) is an example of this type of membrane (see photo 1). This is an FDA approved Class II medical device in which the membrane is clipped between two clear, flexible thermoplastic rings. The ring is designed to provide maximum contact of the membrane with the eye.
There are three levels of ring thicknesses with the thicker rings used for more severe diseases. A thicker ring allows more layers of the amniotic membrane to be applied which extends the treatment time. These membranes are permeable so topical medications can be used concurrently. Patients often report foreign body sensation, but it is usually tolerable (see photo 2). The Prokera Slim has the thinnest, most comfortable ring with a membrane thickness of 100 microns.
The rate that the membrane is digested varies with a quicker absorption being noted with more serious disease. Once the membrane is absorbed, the ring must be removed. The FDA approves keeping the membrane on the eye for up to 30 days, but physicians usually remove it sooner.
Dehydrated amniotic membranes are prepared by using low-heat vacuum to retain devitalized cellular components. These membranes can be stored at room temperature for up to five years. An example of this type of membrane is AmbioDisk (IOP Ophthalmics). This dehydrated tissue in the shape of a disc is very lightweight and care must be used when handling the delicate tissue which is only 35 microns thick (see photo 3). It is placed directly on the eye and held in place with a contact lens. The membrane is usually absorbed within a week, at which time the contact lens can be removed.
Amniotic membrane can also be dried, pulverized and at the time of use reconstituted in sterile saline for topical use. There is some preliminary research suggesting that this amniotic membrane extract can provide similar results to that of an actual graft, but more convenient.
Because these membranes can now be used in a clinical setting, the use has become widespread in managing of a number of diseases. The list includes chemical burns, corneal abrasions, persistent corneal defects, corneal ulcers, limbal stem cell deficiency, Stevens Johnson syndrome, various forms of keratitis (e.g. filamentary), and dry eye syndrome.
Amniotic membranes are useful in the management of dry eye syndrome in which the etiology is often multifactorial but ocular surface inflammation is an important factor. The membrane placed on the eye aborts this inflammatory process. Because the membrane is also rich in nerve growth factor it can help with corneal nerve regeneration which may be important in some dry eye patients.
In a survey of 160 dry eye patients who were treated with amniotic membranes, 95 percent reported the membrane healed their eyes, 93 percent said they felt better and 76 percent said the membrane worked better than previous treatments.
A recent success story from our clinic comes by way of using an AmbioDisk in a 51 year female patient. A year ago she suffered a corneal abrasion which healed but the corneal epithelium was not well attached and she has suffered frequent, extremely painful recurrent corneal epithelial erosions. She is also diabetic and immunosuppressed due to medications following an organ transplant thereby making healing even more difficult. An AmbioDisk was placed on the eye and she has not had a recurrence since and reports markedly improved ocular comfort.
The convenience and effectiveness of these sutureless amniotic membranes are helping to improve outcomes of a wide variety of ocular conditions and the future looks bright for continued growth of this treatment option.
Tammy Than, MS, OD, FAAO is a Professor of Optometry in the UAB Department of Optometry. In 2015, the American Optometric Association honored Than as the AOA Optometric Educator of the Year.