The cornea is the transparent front of the eye made up of 3 layers. A corneal ulcer occurs when some of the outer layer of the cornea is damaged exposing the second layer or even deeper. This may occur due to tear production issues, eyelid dysfunction, trauma, foreign material, congenital abnormalities or infectious causes (e.g. Feline Herpesvirus).
Corneal ulcers are either simple or complicated.
A simple corneal ulcer involves only the corneal epithelium, often heals within 7 days, and does not involve underlying layers.
A complicated corneal ulcer involves the underlying stroma layer and can persist for a longer time. They can develop if there is a delayed normal healing process or if there are factors that can further cause deterioration of the cornea. Secondary bacterial or viral infections, other eye issues such as cataracts, and systemic disease such as Diabetes are just some of the factors that can worsen these ulcers. Sometimes, very severe infection can cause an ulcer to ‘melt’, meaning that the layers are destroyed progressively. These are very difficult to treat and carry a poor prognosis.
Ulcers can vary in appearance depending on the depth, severity and chronicity. Simple ulcers might not be visible to the naked eye. In some cases, you will see visible damage to the cornea and blue-grey discolouration. The animal may be squinting or holding the eye closed and the eye itself may appear red or irritated.
The most common method of testing is via fluorescein staining. The veterinarian is likely to first put a few drops of local anaesthetic into the affected eye to numb it, followed by a green coloured stain called fluorescein. If there is damage to the cornea it will light up green using this stain (moreso under a blue light). It is normal for the stain to drip out of the nostrils as this indicates a patent tear duct.
If a corneal ulcer is infected, or melting, then further testing such as cytology, and culture and sensitivity may be required. This means that samples from the eye (such as the discharge) are collected, examined under the microscope, and potentially cultured in the laboratory to determine the specific infectious organisms.
Whereby trauma is suspected no further diagnostics may be required. However if another underlying causes is suspected, the vet may suggest testing tear production, checking for anatomical abnormalities (such as eyelashes growing in the wrong place and rubbing onto the eye), certain nerve reflexes (such as blinking), using a forcep to look under the conjunctiva and third eyelid tissues for foreign bodies, and even full blood and urine laboratory tests especially if there are other signs of systemic illness.
A topical antibiotic ointment may be prescribed by your veterinarian and is usually sufficient to prevent further or secondary infection, especially for superficial simple ulcers. Systemic pain medication and/or anti-inflammatory medication may be required. If a foreign body is found, it will be removed. However, some patients may require sedation or general anaesthetic to perform this procedure safely.
In more complicated cases, the frequency of ointment application might be increased, and oral antibiotics may be indicated. Underlying causes such as feline herpesvirus and systemic disease e.g. Diabetes may also need to be treated or better managed. Surgical therapy is an option if the ulcer is complicated, melting, deep or simply not responding to medical therapy. This could involve debridement of the surface to stimulate healing, a conjunctival flap or graft to provide corneal support and a direct blood supply, and sometimes even a third eyelid flap (which is where the third eyelid tissues are used to temporarily cover the ulcer like a bandage).
Moreover, if the patient is likely to rub at his or her eye, then we may also recommend an Elizabethan collar to prevent this self-trauma while the ulcer is healing.
Monitoring will also depend on the severity of the ulcer and the individual, but in general, we would recommend a recheck usually in 5 to 7 days, or earlier if you have concerns. This is to make sure that the ulcer is responding well to treatment and to prevent complicated ulcers from forming. If you have any further questions, please always feel free to contact your vet first to discuss.