The cornea is the clear part at the front of the eye. Its layered structure is vitally important to maintain a transparent pathway for light to pass into the eye, and so is critical for clarity of vision. The layers are known as the epithelium, stroma and endothelium.

The outermost layer is only 10-20 cells thick and is called the epithelium of the cornea. If this layer is damaged it is known as a corneal ulcer, and the exposure of nerve endings result in pain. Generally, this is seen in your pet as a watery eye, faster blink rate or holding the affected eye closed, and rubbing at the face. Usually a simple superficial corneal ulcer will heal very quickly; within seven days. This happens because the surrounding epithelial cells slide across and then stick to the layer beneath. 

Treatment of superficial ulcers mostly relies on lubrication and sometimes topical antibiotic medications. 

Although superficial ulcers should heal very quickly, in some cases this does not happen. This type of ulcer is called a ‘non-healing ulcer’ and can take a period of several months to heal, and even though superficial is still at some risk of corneal melt developing. In the case of non-healing ulcers, the epithelium tries to slide across but is unable to stick to the layer underneath and instead becomes ‘under-run’. Non-healing ulcers usually require some surgical procedure to promote healing. Treatment options include use of a corneal diamond burr, which can be performed conscious; or a surgical micropunctate keratectomy with or without nictitating membrane flap. The flap will cover the eye and remain in place for a period of up to three weeks. These under-run ulcers are most common in older pets.

The middle layer of the cornea is known as the stroma, and this is much thicker. Some breeds of dog – most commonly the ones with flat faces such as pugs and bulldogs – are prone to developing ulcers involving this deeper layer of the cornea, known as deep corneal ulcers. If this involves more than half of the stromal depth usually surgery is required to help them heal. Very deep ulcers are at risk of rupturing, and can lead to loss of the eye.

Treatment of deep corneal ulcers usually requires surgery, commonly involving a grafting procedure to provide nutrients for healing via blood vessels. Grafts also give some support to help reduce the risk of the eye rupturing. Grafts can either be created from the conjunctiva (pink tissue around the eye itself and the inner surface of the eyelids) of from healthy cornea via a corneo-conjunctival transposition. The graft is sutured in place with an exceptionally fine suture material, and is usually left in situ either permanently or semi-permanently, to improve the health of the cornea nearby. Depending on where the original ulcer was located, this may impact on vision slightly, but in this case the goal is to save the eye. Alternative treatments include the use of processed healing/assisting products such as collagen or amnion, and if the cornea is very unhealthy the use of corneal cross-linking may be employed.