BLOG: Why do we use glue on the eye?

If you Google “ocular Super Glue” you mostly get entries about people accidentally instilling superglue into their eyes. It’s usually kids playing with glue or adults mistaking the tube of glue for their ocular ointment (which brings to mind ear wax drops into the eye).

But if you Google “ocular glue” you get entries about this month’s topic: corneal glue and other ocular sealants.

A lot of us have heard of the use of glue for corneal problems but have never seen it done or observed it in the eye. So, we’ll try to do more than just scratch the surface of this sticky topic (the only pun, I promise).

Corneal glue is used in cases of corneal perforation or in a progressive thinning where perforation is feared. Perforation is almost always caused by a trauma or an infection that has dangerously progressed. The goal of the glue is to restore the globe’s structural integrity; a wound leak can cause anterior chamber flattening, hypotony, choroidal detachment and infection/endophthalmitis. Glue can stop the perforation from expanding to a larger hole and allows the stroma to start to heal or form a scar. If the scar is central, then the patient might still be headed for keratoplasty in the future, but at least the glue could buy some time until the eye is less inflamed, giving the surgery a better chance at success.

Despite what you may have thought, corneal specialists do not use commercial “Super Glue” on the cornea, which is more toxic than other alternatives. Incidentally, Super Glue is still a registered trademark of Super Glue Corp. All of these types of adhesives are called cyanoacrylate glues, which were first developed in the early 1940s during work on materials for the war. The most commonly used cyanoacrylates in eye care are Histoacryl Topical Skin Adhesive (TissueSeal), Nexacryl (Tri-Point Medical), Isodent by SpofaDental (often used in dental procedures) and Dermabond by Ethicon (the sutureless skin adhesive). These glues are all cyanoacrylates, but the tissue adhesives have isobutyl or octyl groups of carbon bonded to the cyanoacrylate ester, whereas the commercial glue has a methyl group. Commercial cyanoacrylates are not recommended for corneal adhesion – in fact, no corneal adhesive is FDA approved – but the tissue adhesives mentioned previously are considered a standard treatment.

The technique of applying glue to the cornea can be summed up by the phrase, “Keep it dry and apply it fast.” The glue will start its polymerization (hardening process) when it gets wet. So, it’s imperative to keep the surface of the stroma dry, to allow the glue to bond with the stroma, as opposed to the glue solidifying before it can adhere to the perforation. It’s best to have the patient lying prone under a surgical microscope (so gravity can assist), but it can be done at the slit lamp. Topical anesthetic is administered and an eyelid speculum placed. Weck-cel sponges are used to débride the surrounding epithelium (as the glue does not adhere well to epithelial cells) and to keep the stroma as dry as possible. An aliquot of glue is drawn into a 30-gauge needle and placed in the (recently dried-off) corneal perforation, with care to not over-fill, as the glue expands as it solidifies. If too much glue is used, the glue will protrude too far anterior (or posterior) to the cornea. The glue starts to polymerize quickly, within seconds, depending on how much wetness is in the wound. Once the specialist determines that the glue is bonded to the perforation and is dry, the wound should be tested for Seidel’s sign, and a soft bandage contact lens is placed (as the surface of the glue is very hard and scratchy). The patient is prescribed aqueous humor suppressants (to keep the pressure on the plug lessened), artificial tears (to keep the contact lens from drying out) and antibiotics (to treat – or prevent – infection).

The contact lens is left on for as long as the glue is in place, and the glue is left on (ideally) until it spontaneously sloughs off. The glue is displaced anteriorly when the stroma zippers together or when scar tissue forms. In both processes, re-epithelialization occurs under the glue, further weakening its bond to the stroma. Complications include: the need to reapply the glue (because the original bond was too weak), giant papillary conjunctivitis (elevation of surface and contact lens over wear), iridocorneal adhesion (due to the glue escaping into the anterior chamber) and a secondary microbial infiltration around the glue (rare, but possible).

For the treatment of corneal perforations, there are also biologic glues (or fibrin glues) such as Tisseel Fibrin Sealant (Baxter) or Evicel Fibrin Sealant (Ethicon), which are FDA-approved for corneal application. These glues solidify less quickly than cyanoacrylates (which makes application easier), are softer and smoother, can be used under an amniotic membrane and may have faster healing times. Disadvantages of fibrins include a complex mixing process, cost, lower tensile strength and possible promotion of microbial growth (cyanoacrylates are bacteriostatic). There’s also ReSure ocular sealant (Ocular Therapeutix), a hydrogel (not a cyanoacrylate) recently approved for clear corneal incisions in cataract surgery.

Right now in the world of eye care, glues are used primarily in cases of perforation concern. However, even if you don’t routinely treat these cases, it’s important to understand this treatment modality. As sealant technology improves, its applications will only increase.

References:

Krachmer J, Mannis M, Holland E. Cornea. 3rd ed. Management of Corneal Perforations. Mosby Elsevier; 2011.

Kenyon KR. Ophthalmology. 1982;89:634-635.

Sharma A, et al. Ophthalmology. 2003;110(2):291-298.

Bhatia S. Ocul Surf. 2006;4:146-154.