Corneal Clarity

A Lifeline for the Sick Ocular Surface

By Thomas John, MD

Damaged, malfunctioning, compromised or devitalized ocular surface tissue needs to be replaced with an alternative tissue source in order to achieve regeneration, ocular surface re-stabilization and to improve the quality of vision and patient comfort. With such a focus, regenerative medicine is clearly the next new horizon of medical treatments. While waiting for this horizon to materialize fully, we need to take advantage of the current options that are available to treat ocular surface diseases. One such treatment modality is the use of amniotic membrane (AM).

Grabbing the “Eye-Line”

If placenta is the “life-line” for the growing fetus, then amniotic membrane may be the “eye-line” for compromised ocular surface. Clinicians are always interested in the ocular surface because it is essential for the visual quality of their patients. In the United States, two types of AM are commercially available: cryopreserved and freeze-dried. AMs are used for a variety of ocular-surface diseases, including pterygium, symblepharon, ocular surface burns, compromised glaucoma blebs, strabismus surgery, toxic epidermal necrolysis (TEN) and Stevens-Johnson syndrome (SJS).

While the patient's conjunctiva may be considered for the most part superior to any amniotic membrane, such auto graft tissue may not be readily available due to scarring from previous surgeries, or to past disease processes. Please note that while the use of AM shortens surgery time (there is no need to harvest donor conjunctiva), it does increase the cost of such procedures.

AM History

As early as the 1900s, fetal membranes were used in skin transplantation to treat skin burns with positive results. However, it was not until the mid-1940s that AM was first used on the ocular surface. It took another half a century before it began to emerge as an ophthalmic surgical treatment modality. AM has inherent benefits of promoting wound healing by accelerating surface epithelialization at the same time that it has a dampening effect on angiogenesis, scarring and inflammation. Such properties, along with AM's commercial availability, have contributed to its increased use in the ophthalmic surgical field. It covers the span of ocular surface surgery — conjunctiva, limbus and the cornea.

On the corneal surface, AM can help promote healing of a persistent epithelial defect, while in the limbal region it can assist in limbal stem-cell transplantation or in ex-vivo expansion of limbal stem cells for transplantation. On the conjunctiva, it can help deepithelialized surface from adhering and causing symblepharon and fornix foreshortening by lining the two opposing de-epithelialized surfaces.

The How-To

The question then arises, how do I use AM? There are several approaches to the surgical techniques, depending on the indication. For persistent epithelial defect without stromal loss, a single layer of AM may be attached to the corneal surface with non-absorbable, 10-0 nylon sutures, with or without concurrent use of tissue adhesive such as fibrin glue. For stromal loss, such as a sterile corneal ulcer, the AM may be folded on itself to fill the defect, and held in place with sutures and a second layer placed on top, much like a protective layer (Figure 1). For stem cell transplantation, AM may be used as a carrier sheet, or a two-layered AM with stem cells in between the AMs, in a sandwich technique. On the conjunctival surface, following pterygium excision, the bare sclera may be covered with an AM transplant.

Figure 1. Multi-layered approach of AM transplantation in corneal melt with central Descemetocele.

In more extensive conjunctival loss as in SJS, TEN or alkali burn, more extensive covering of the ocular surface is carried out with suture anchoring of the AM deep in the fornix. While fibrin glue can be used to decrease or eliminate sutures in some cases, keep in mind the limited tensile strength of fibrin glue and the potential for partial tissue detachment postoperatively.

Researchers in Europe are exploring the use of AM extract to promote ocular surface healing while dampening inflammation. The extract is a lyophilized powder, which is used as an eye drop after reconstitution with sterile saline solution. It is not now available in the US. This approach takes the treatment from the operating room to the physician's office.

Thus, regarding ocular surface management, the present is good, and the future may be even better… stay tuned! OM

Thomas John, MD, a world leader in lamellar corneal surgery, is a clinical associate professor at Loyola University at Chicago, and in private practice in Oak Brook, Tinley Park and Oak Lawn, III. E-mail him at tjcornea@gmail.com.