Indolent ulcers, also known as spontaneous chronic corneal epithelial defects (SCCEDs), non-healing ulcers, recurrent epithelial erosions and Boxer ulcers etc. most commonly occur in middle-aged to old dogs. They are occasionally seen in cats. Clinically they present as superficial erosions which are not infected and fail to heal by the usual epithelial wound healing process. They can occur in any breed but are often associated with certain breeds, such as the Boxer, Staffordshire Bull Terrier and Corgi. Ophthalmic examination reveals that the ulcer is surrounded by a rim of non-adherent epithelium. The application of fluorescein characteristically results in seeping of the stain under this layer, giving a fainter slightly 'fuzzy' green edge to the defect (Figure 1). Dogs with this condition show varying amounts of blepharospasm and corneal neovascularisation, and if left untreated or inappropriately treated the ulcers can persist for weeks or even months. The underlying problem here is failure of the sheets of migrating epithelial cells to form a new basement membrane and therefore permanent attachment to the underlying stroma. Histological studies demonstrate the presence of a superficial acellular hyaline zone in the area of the erosion.

Figure 1. Characteristic fluorescein staining pattern of an indolent ulcer.

The aim of therapy is to disrupt or remove the abnormal basement membrane using a keratotomy or keratectomy. As well as removing the abnormal matrix these procedures also damage the corneal stroma and stimulate the stromal wound-healing response. This promotes fibroblast involvement and good epithelial cell adhesion. Scaring and vascularisation can occur as a result of these therapies but this is not always a bad thing, as once the epithelium has covered the defect it usually subsides spontaneously.

At the very least debridement of the loose epithelial sheets should be performed. This can be done under topical anaesthesia and can then be followed up with one of the techniques to disrupt the anterior stroma. These include punctate and grid keratotomy as well as phenol cautery (no longer routinely used but still a useful technique). These may need to be repeated several times before the ulcer is fully healed (Figure 2). Various studies have been published describing these different procedures and between 70% and 90% healing rates have been reported. In those cases that still fail to heal a superficial keratectomy performed under general anaesthesia, using magnification (preferably an operating microscope) is recommended. In the hands of an ophthalmologist this will result in 100% heal rates within 7–14 days postoperatively. Placement of a contact lens post keratotomy or keratectomy subjectively improves the patient's comfort level. Third eyelid flaps are also used in some cases but have the disadvantage of preventing visualisation of postoperative events.

Also described but not routinely used to treat these ulcers are thermal keratoplasty and cyanoacrylate tissue adhesive.

Medical treatment should be used as an adjunct to surgery but on its own will not result in resolution of these defects. Pain relief is important because patients with these superficial lesions can be very uncomfortable. Systemic non-steroidal anti-inflammatory drugs are recommended for this. Antibiotic cover should be used following keratotomy and keratectomy as, although the ulcers are not usually infected, bacteria can be introduced into the ulcer by the procedure. Systemic antibiotics are favoured by the author as frequent application of topical therapy can be both irritating for the patient and may slow down the healing response due to the presence of preservatives and wetting agents which are toxic to epithelial cells.

In summary, as soon as the diagnosis of indolent ulcer is made debridement and keratotomy should be performed ideally under topical anaesthesia, with or without sedation. If the ulcer does not heal after a few of these procedures (usually three in the author's hands) then a superficial keratectomy is recommended.

Figure 2. (A) Ulcer post phenol having had a previously unsuccessful grid keratotomy. (B) The same ulcer 7 days later fully healed.