SURGERY OPTIONS

Surgery has both diagnostic and therapeutic applications in the management of infectious keratitis and related ocular surface complications. Speaking at the 4th EuCornea Congress in Amsterdam, Harminder S Dua MD, discussed the role of various surgical techniques and provided an array of helpful tips.

Alcohol delamination of the corneal epithelium by applying 20 per cent alcohol to the area of interest on the cornea for 30-40 seconds offers a method of obtaining tissue for biopsy and may be therapeutic as well. The removed sheet of epithelium can easily be spread flat, and when fixed, gives very good morphology for histological examination (Figure 1). However, due to the toxicity of the alcohol, the specimen cannot be used for culture, said Dr Dua, chair and professor of ophthalmology, University of Nottingham, Queens Medical Centre, Nottingham, UK.

Discussing stromal biopsy, Dr Dua recommended acquiring two samples, one for microbiological assessment and the other for histopathology, and obtaining the histopathology specimen at the junction of the affected and unaffected tissue (Figure 2). The procedure can be performed using a skin biopsy punch, although depending on the depth of the infiltrate, it may be necessary to first raise a flap of the cornea before using the punch. If there is concern about inadvertently perforating through the cornea, an alternative technique is to create a superficial mark with a trephine, deepen the cut with a diamond blade and then use a crescent blade to shave off the base.

Dr Dua discussed some applications using tissue glues. Small perforations may be sealed using cyanoacrylate products. However, safety and success with this technique requires that surgeons use just a minimal amount of glue and first debride away any loose epithelium, otherwise the glue will fall off. In cases of corneal perforation with iris incarceration, Dr Dua described a technique involving a double drape tectonic patch. The first patch is applied without glue to cover the exposed iris and the second larger patch with glue is applied directly over it.

He also described the use of fibrin glue tissue adhesive to successfully address a persistent leak at the graft-host junction in an eye that had undergone a fourth penetrating keratoplasty (PK). The glue was injected at the graft-host junction and allowed to enter the anterior chamber underlying the leak. Dr Dua explained the idea occurred to him based on his experience using fibrin glue to manage leaking glaucoma filtering blebs, where he injects the glue in the bleb as an alternative to autologous blood. “This is an approach for surgeons to consider if they encounter a fluid leak post-PK, although my positive experience using it represents just a single case.”

Fibrin glue is also being used as an alternative to sutures in amniotic membrane transplantation and has advantages for causing less irritation and avoiding the need for suture removal. With respect to the use of amniotic membrane, its transplantation in eyes with active infectious keratitis may serve a dual purpose, acting both as graft tissue and as a drug reservoir. “Emerging evidence indicates that amniotic membrane transplantation may improve outcomes in eyes with treatment-refractory infectious keratitis, possibly because the material holds the topically applied antibiotic or antiviral agent and augments its delivery to the target site,” Dr Dua said (Figure 3).

He reminded corneal surgeons that deep anterior lamellar keratoplasty (DALK) is a useful alternative to PK when the indication for a graft procedure is post-viral scarring since eyes with viral keratitis have a high risk of rejection post-PK. However, it is important to evaluate corneal sensation in these cases, as it is a prognostic indicator. “Failure of the graft in eyes with viral keratitis is not necessarily due to rejection but rather may be associated with neurotrophic non-healing of the graft-host junction and related problems,” he said.

When performing a graft procedure in eyes with a history of herpetic infection, Dr Dua also reinforced the importance of antiviral prophylaxis to prevent viral recurrence. In patients who are undergoing a transplant procedure for infective keratitis and are in need of cataract surgery, he recommended following a staged approach if there is any suspicion of active infection, leaving the cataract operation for a later time. Dr Dua also discussed the use of fine needle diathermy using monopolar cautery as a method for occluding established corneal vessels and for treating lipid keratopathy, which is most often due to virus infectionrelated vascularisation (Figure 4).

“Some surgeons may wonder if anti- VEGF treatment is a better alternative for obliterating corneal vessels. However, anti-VEGF agents act only on vessels that are actively growing and do not affect established, mature vasculature,” Dr Dua said. Anit-VEGFs and fine needle diathermy can be combined. He concluded his review with a discussion of “advances” that go back to the past. He suggested that when all else fails for treating infection, surgeons may consider destructive techniques, including cryotherapy, cautery with silver nitrate, or use of povidone-iodine.

“These old methods may be useful to get rid of anything live, but in the effort to eradicate infection they will also kill the host cells. Collagen cross-linking for treatment of infective keratitis may prove to be a viable alternative,” Dr Dua said.