Making Sense of Amniotic Membranes

Amniotic membranes are useful in treating certain ocular conditions, but if you’re confused about when to integrate them into your treatment plan, you’re not alone. These medical devices may seem pretty similar, but they’re actually quite distinct. This article breaks down the differences between the two main types of amniotic membranes and explains when it would be appropriate to consider the use of an amniotic membrane in the treatment of a particular patient or condition.

AMNIOTIC MEMBRANES: WHAT’S WHAT

The amniotic membrane is the inner lining of the placental tissue of a live donor. Pregnant patients are screened for communicable diseases before the tissue is harvested during an elective C-section in an FDA-approved protocol. Any donor cells that would cause graft rejection are removed via the preservation and sterilization processes, so nothing is left from the donor that retains the original cellular structure that would cause a reaction.

There are two main types of amniotic membranes used for ophthalmic purposes: cryopreserved and dehydrated (Table). Cryopreserved amniotic membranes have a shelf life of about 2 years and must be stored in a refrigerator or freezer. Dehydrated, or lyophilized (freeze- or air-dried), membranes have a shelf life of about 5 years. This type of membrane is useful if you are working in a location that doesn’t have refrigeration, electricity, or water (think military situations).

Application

Applying cryopreserved membranes is similar to inserting a regular contact lens: While the patient looks down, slip the membrane under the upper lid. It will settle and sit on the front surface of the eye (Figure). Many doctors tape the eye afterward to stabilize the membrane. The patient will need to return to your office in 2 to 10 days to have the polymethylmethacrylate (PMMA) ring removed.

It takes more time to place a dehydrated amniotic membrane, and there’s a bit of a learning curve to smoothing it out and making sure there are no wrinkles underneath it. Use a Weck-Cel sponge (Beaver-Visitec) to ensure all surfaces are dry; otherwise, the membrane will slide right off. Most doctors use a speculum to tamp down/rub the dry membrane on the surface of the cornea and then dry off the cornea with the Weck-Cel sponge, as well as the back of the bandage contact lens. Everything that’s dry has to stay dry. The dehydrated membrane will dissolve over time, but the patient will need to return to have the bandage contact lens removed.

Bandage contact lenses and dry or lyophilized amniotic membranes, which are freeze-dried, are indicated only for wound coverage. The cryopreserved amniotic membrane retains a key matrix component called heavy chain-hyaluronic acid/pentraxin 3 (HC-HA/PTX3). All by itself, HC-HA/PTX3 is the molecule that does the heavy hitting of actual wound healing. This is the only amniotic membrane option approved by the FDA to promote wound healing. (The other options are only approved for wound coverage.)

The HC-HA/PTX3 molecule works in a variety of pathways. Used in cryopreserved amniotic membranes, HC-HA/PTX3 promotes healing by preventing the growth of fibronectin, which prevents the ability to make scars. HC-HA/PTX3 also has antiinflammatory properties via suppression of TH-1 and TH-17, which are lymphocytes that specifically attack the ocular surface. (They’re the same TH-1 and TH-17 molecules that lifitegrast ophthalmic solution 5% [Xiidra, Bausch + Lomb] targets.) Additionally, HC-HA/PTX3 supports the healthy turnover of corneal epithelial stem cells.

Complications

One thing that can get tricky is if you have a patient who reacts to a dry or lyophilized membrane (eg, the membrane sticks to the cornea after it rehydrates). In this case, the only way of removing it is to mechanically scrape it off—or debride the membrane. If a patient isn’t tolerating a cryopreserved membrane, you can just pop it out like a contact lens.

The PMMA ring with the cryopreserved amniotic membrane isn’t very comfortable. Patients can usually tolerate it, but if you have a patient who is struggling with it and you need to repeat the procedure, you might consider switching to a dry or freeze-dried membrane.

Additionally, some patients (eg, those with blebs) aren’t candidates for a cryopreserved amniotic membrane. (Patients with blebs may experience the PMMA ring rubbing on the bleb, which is obviously something you want to avoid.) Also, patients with allergies to any of the ingredients in the cryopreserved solutions (eg, ciprofloxacin or amphotericin B) are not suitable candidates for a cryopreserved amniotic membrane.

INDICATIONS

For some doctors, bandage contact lenses may be the go-to for treating certain trauma cases, but before you reach for this option, take a moment to consider whether an amniotic membrane would be a better choice. Yes, amniotic membranes take an extra billing step and a bit of patient communication, but don’t deprive appropriate patients the healing benefits that come with their use.

In primary care settings, the most common uses for amniotic membranes are trauma or injury (eg, corneal abrasions) and herpetic lesions. Those who, like me, specialize in dry eye and don’t see as many urgent cases, are typically caring for patients with chronic conditions and, thus use amniotic membranes a bit differently.

Punctate Keratitis

If you have a patient with superficial punctate keratitis (SPK) that is not responding well or nonresolving, you can place a cryopreserved amniotic membrane to help keep that cornea healed for quite a few months. It’s usually not monotherapy for me in dry eye. I re-epithelialize moderate-to-severe corneas with the Prokera Slim (BioTissue) cryopreserved membrane, and then I try to protect that tissue by attacking the underlying causes of the patient’s dry eye. That’s the best way I’ve found to integrate an amniotic membrane into therapy. I find that many therapies are much more comfortable after using Prokera first because you’re not dealing with a cornea that’s hypersensitive and irritated. So, it tends to be first-line therapy for me in patients with punctate epithelial erosions or SPK of grade three or more.

Dry Eye

Several studies have shown that as few as 3 days of wearing a cryopreserved amniotic membrane can lead to about 3 months of dry eye symptom resolution.^1,2 This is great for patients who do not have the ability or the dexterity to instill eye drops or do any home therapy, but it won’t fix everything, because the root cause of their dry eye (eg, lifestyle factors, systemic disease, exposure) is still going to be there.

CONSIDER AMNIOTIC MEMBRANES IN YOUR TREATMENT TOOLBOX

Any time you have a cornea that could use some re-epithelialization and healing, consider an amniotic membrane. And if you have a patient with an ocular injury, think about reaching for a cryopreserved amniotic membrane. Keep in mind, too, that this treatment option has antibiotic properties for both Gram-positive and Gram-negative strains of bacteria, so if you’re concerned about a patient needing coverage, but you’re also worried about infection, an amniotic membrane may potentially be safer than a bandage contact lens. This is why they are great for wound coverage in herpetic cases and the like.

Consider a cryopreserved amniotic membrane over the use of a bandage contact lens if you’re looking for actual healing (rather than simply wound coverage) and for reducing scarring, as well as the risk of inflammation and infection.

Still craving additional insights on amniotic membranes? Outside of learning from your local rep, the American Academy of Optometry usually has a workshop at its annual national meeting, and that’s coming up in a few months, so keep an eye out.