What is the cornea?
The cornea is the clear, shiny membrane that makes up the front of the eyeball. The cornea is composed of four layers. The most superficial layer is the ‘epithelium’, which is comprised of several thin layers of cells. Below the epithelium is the ‘stroma’, which is the thickest layer. Below the stroma is a thin elastic layer called ‘Descemet’s membrane’, and the very thin inside lining of the cornea is called the ‘endothelium’. A corneal ulcer refres to damage to any or a combination of these layers of the cornea.
What is a corneal ulcer?
An erosion of a few layers of the epithelium is called a ‘corneal erosion’ If the damage extends into the stroma, it is called a ‘corneal ulcer’. If the ulcer extends to the level of Descemet’s membrane, it is called a ‘descemetocoele’. If the ulcer perforates, the liquid inside the eyeball leaks out, the eye collapses, and irreparable damage occurs.
What causes a corneal ulcer?
Corneal ulcers can be caused by trauma from:
- cat scratches
- chemical burns (from shampoos for example)
- bacterial and viral infections
- foreign bodies like grass seeds
- irritation from eyelid abnormalities.
Some breeds of dogs, such as Boxers, have genetic corneal abnormalities predisposing them to ulcers.
Corneal ulcers are painful. Shutting the eye or excessive blinking or spasm of the eyelids and a watery discharge are common signs. The pet may avoid bright light.
A corneal ulcer is diagnosed by examination and use of ‘fluorescein stain’, which adheres to ulcerated areas. Special lights will make the stain ‘fluoresce’. If the ulcer is very deep, samples may be taken for culture and cytology.
The appropriate treatment for a corneal ulcer depends on how deep it is. A superficial ulcer will generally heal without problems in three to five days. An antibiotic drop or ointment may be used during this time to prevent any bacterial infection. Sometimes, dead cells at the edges of the ulcer interfere with the healing process and need to be scraped away.
Deeper ulcers require more treatment. The cornea normally has no blood supply and healing occurs by migration of blood vessels from the sclera (the white of the eye). Surgical procedures for deeper ulcers are aimed at supporting and protecting the eye and bringing the blood supply to the corneal ulcer. This is achieved by temporarily stitching the ‘third eyelid’ across the eye or stitching the eyelids together. Once the ulcer is healed, the stitches are removed and the pet can use the eye again.
Very deep ulcer
Very deep ulcers require a conjunctival graft, in which a strip of the conjunctiva is sutured permanently into the ulcer, to fill the hole and bring in blood vessels. With time, these grafts gradually become more transparent. Along with surgical procedures, intensive treatment with both eyedrops and tablets may be needed to treat infection and inflammation of the cornea and internal parts of the eye. Sometimes, referral to an eye specialist may be recommended for deep ulcers with risk of perforation.
Corneal ulcers can progress quickly from superficial to deep ulcers. It is very important to have any eye problems checked early to avoid complications. Some eye medications can make ulcers worse, so do not apply any drops or ointments unless advised to do so by the veterinarian. The vet will need to monitor the ulcer regularly to ensure healing is progressing. Blood vessels that have migrated into the cornea during the healing process will remain afterwards. These gradually regress, but sometimes drops or ointments will be recommended to help the process along.
If you have noticed any of the symptoms of corneal ulcers in your pet, bring them to your nearest Greencross Vets immediately. The sooner the issue is treated, the greater the chance of healing.