August 2019

CORNEA

Pharmaceutical Focus
Ocular uses of amniotic membrane


by Maxine Lipner EyeWorld Senior Contributing Writer


Dehydrated amniotic membrane is trimmed with scissors to an appropriate size to use as a graft after pterygium removal.
Source: John Hovanesian, MD

 

From pterygium surgery to Stevens- Johnson syndrome and more, amniotic membrane has a definite niche in ophthalmic practice. Amniotic membrane has two main roles, according to Darren Gregory, MD. “It can act like a bandage and provide an anti-inflammatory effect, or it can serve as a tissue substitute to fill a hole and provide a foundation that epithelium can grow onto,” he said.
For acute Stevens-Johnson syndrome, Dr. Gregory finds that amniotic membrane can be a real game-changer in preventing severe scarring complications. The membrane helps to quell inflammation and allow damaged conjunctiva to heal in with a relatively normal mucosal epithelium. “But there’s a window of opportunity in the first week of the disease when it is most effective,” Dr. Gregory said.
Edward Holland, MD, finds that for recurrent or very large pterygium where there might not be enough conjunctiva to do a free conjunctival graft, amniotic membrane can be a good conjunctival substitute. This is also true for ocular surface reconstruction such as limbal stem cell transplantation with a bare area of sclera that needs to be covered and in corneal surface reconstruction, especially where there’s thinning and concern about potential perforation, he noted. He also uses amniotic membrane when he must scrape a large area of the cornea that can lead to slow healing, such as some cases of Salzmann’s nodules. “I think the amnion makes the patient more comfortable when they have a large defect,” Dr. Holland said. It also reduces secondary neovascularization, he finds.
Amniotic membrane can mistakenly be used in limbal stem cell failure. “It doesn’t supply limbal stem cells,” Dr. Holland said, adding, however, that when there is partial failure of two or three clock hours in which you want to scrape away abnormal corneal epithelium, it can be used to cover the area and allow healthy corneal epithelium to grow before conjunctiva invades.
For pterygium surgery with amniotic membrane, John Hovanesian, MD, finds it exerts an antifibrotic and anti-inflammatory effect that reduces the risk of recurrence. Adding this to the equation with mitomycin-C reduces the regrowth rate from 50% to around 5%, he noted.
The two different forms of amniotic membrane include cryopreserved and dehydrated. “With cryopreservation the tissue is frozen; it requires cold temperatures to maintain it, which creates a little more difficulty with shipping and storage, but it’s effective,” Dr. Hovanesian said. The dehydrated form is dried and terminally radiated to kill any contaminants but then is shelf-stable. “Because of that, there’s a lower cost,” he said. “There’s not any real evidence that one is better than the other. Experienced clinicians usually say it’s up to the physician which type of material they prefer handling and which is more comfortable for the patient.”
Dr. Holland doesn’t think the dehydrated form works quite as well. “If it’s a sight-threatening case and I want the best amnion, I use cryopreserved,” Dr. Holland said. “But if it’s a persistent epithelial defect and we’re using it for a smaller corneal lesion, then I use the dehydrated form because of its convenience.”
The self-retained cryopreserved form of amniotic membrane is known as Prokera (Bio-Tissue), and the dehydrated form is known as AmbioDisk (Katena). With Prokera, a plastic ring is attached to the amniotic membrane, which is stretched across it like a drumhead, Dr. Hovanesian noted. With AmbioDisk, dried amniotic membrane is paired with a soft contact lens. Dr. Hovanesian finds both work well but has concerns that more patients experience pain with Prokera because of the ring. “These eyes are almost always inflamed and when you put a foreign object on top of that, they often will react,” he said.
Dr. Gregory pointed out that while the self-retained amniotic membrane is quick and easy to apply, it’s not always the best way to use the membrane. For example, in Stevens-Johnson syndrome, Prokera doesn’t cover enough of the eyes to be fully effective on its own, he said. Prokera can be used to cover the cornea, but in cases where there is extensive conjunctival sloughing, he will cover those areas with a sheet of amniotic membrane fixated with sutures. Fibrin glue can be used to attach amniotic membrane, but it does not work as well if some of the membrane extends over areas of intact epithelium, as is often the case in Stevens-Johnson syndrome.
Another form sometimes used is amniotic fluid drops, which have benefits for patients who have a non-healing epithelial defect such as a neurotrophic ulcer. “I’ve had patients who have partial limbal stem cell deficiency and they have a hard time maintaining a healthy epithelial layer on the cornea,” he said, adding that while he has only tried this in a handful of cases, it seems to have helped heal epithelial defects when other significant measures have not.
Overall, in Dr. Hovanesian’s view, if physicians treat ocular surface disease and pterygium, using amniotic membrane will advance the standard of care that they offer patients.

About the doctors

Darren Gregory, MD
Associate professor of ophthalmology
University of Colorado, Denver

Edward Holland, MD
Professor of ophthalmology
University of Cincinnati

John Hovanesian, MD
Harvard Eye Associates
Laguna Hills, California

Contact information

Gregory
: Darren.Gregory@ucdenver.edu
Holland: eholland@holprovision.com
Hovanesian: jhovanesian@harvardeye.com

Financial interests

Gregory
: None
Holland: BioTissue
Hovanesian: Katena

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