Corneal Ulceration

My pet’s eye is half-closed and there seems to be something in their eye

What is a corneal ulcer?

A corneal ulcer is damage to the corneal surface, which is the thin, clear covering of the eye. The cornea is made up of three layers: the outer epithelium, the stroma (which is thickest and acts as the scaffold) and the Descemet membrane. All three layers are transparent, allowing light to enter the pupil and create an image that our brain interprets as the sights we see around us.

How does a corneal ulcer occur?

The most common cause of an ulcer on the cornea is due to trauma. Damage may occur from a sharp object like a cat scratch or from your pet rubbing their eye on a rough surface. Damage can also occur from chemical irritation like getting shampoo in the eye or even if something rough gets caught under the eyelid, scratching the eye every time they blink.

Infections from viruses or bacteria can also lead to corneal ulceration. There are some systemic diseases that can lead to corneal ulcers such as diabetes mellitus, Cushing’s disease or low thyroid hormone levels (hypothyroidism).

Corneal ulcers can also occur due to lack of sufficient lubrication of the eye. This is a medical condition called keratoconjunctivitis sicca (KCS), commonly known as ‘dry eye’.

Some breeds such as the boxer can inherit a degenerative condition called epithelial dystrophy. Epithelial dystrophy causes a weakening of the outermost surface (epithelial layer) of the cornea, easily leading to corneal ulceration.

How bad is a corneal ulcer?

Damage to the cornea is characterised into three parts depending on the depth and severity of the injury.

The superficial injury to the outermost surface (epithelium) is called a corneal abrasion or erosion.

Damage that extends past the epithelium into the stromal layer is termed a corneal ulcer.

Injury that extends through the stroma and affects the final layer of Descemet membrane is called a Descemetocele. If this final layer is damaged and the outer surface of the cornea is ruptured, the globe of the eye will lose its structure the animal will lose their eye.

How do I know if my pet has a corneal ulcer?

Corneal ulcers are painful. If a pet has a corneal ulcer, they will usually keep their eye tightly closed, often tearing excessively and often pawing/rubbing at their eye. When the eye is opened, the white of the eye (the sclera) is often red and the area around the eye known as the conjunctiva may be pink due to the irritation and may be swollen. In the cases of large ulcers a depression or even a crater-like cavity can be seen on the surface of the eye. The outer edges of the ulcer absorb moisture from the tears and can appear cloudy or even white. This change is called corneal oedema and is sometimes the only sign that there has been damage to the surface of the eye.

Can a corneal ulcer be treated?

Yes. Corneal ulcers should be treated, even if they appear small and insignificant. Once the outer epithelium of the eye has been damaged, bacteria often take advantage of the opening and can start colonising the now vulnerable second or stromal layer. Once bacteria have a foothold they cause the ulcer to degenerate and enlarge, potentially to the point of loss of the eye. Corneal ulcers are not to be scoffed at.

What will the vet do if my pet has a corneal ulcer?

When the vet examines your pet’s eye they will use a fluorescein dye that will cause a colour change to show the presence of damage to the cornea. With a special ophthalmic light, this allows the vet to visualise the extent of the damage and also monitor the ulcer size once treatment has begun.

Corneal ulcers are usually treated with antibiotic eye drops and the vet may also prescribe eye drops or oral medication for pain. The vet may also include anti-inflammatory eye drops to reduce the swelling and inflammation in and around the eye. There are some eye drops for animals that contain cortisone, which should never be used when an animal has corneal ulceration. It is really important that you don’t just get drops from a friend whose animal had an eye condition and start putting that your animal’s eyes. Similarly, you should also not use just any human eye drops, as this medication may be contra-indicated. In South Africa, as a result of the pet population being significantly smaller than the USA or European markets, some pharmaceutical companies do not register their products here. This means that in some instances, the vet may have to rely on a human medication. This is called extra label use, and the vet will take care to use a product that is compatible with your pet.

Antibiotic eye drops are only active for a few hours and as such need to be applied often. Depending on the severity of the ulcer, this can be from every hour to every four hours. Other eye drops, such as Atropine eye drops are active for much longer and usually only need to be applied once or twice a day. The vet will give you proper instructions as to how often to use the medicine prescribed.

It is important to continue treatment as per the veterinarian’s recommendations and not discontinue treatment too early, even if you see improvement. Speak to the vet if you are unsure.

The vet will most likely demonstrate to you how to apply the eye drops during the consultation for the eye problem and ensure you are comfortable applying them yourself before you go home.

The vet may advise on the use of an Elizabethan collar, known as the ‘cone of shame’, to prevent your pet from scratching and doing more damage to an already injured eye. This prevents paws and sharp nails from reaching the eye and is recommended until treatment is complete or the pain is under control.

Will my pet need another visit after treatment has started?

Yes, most vets require a check-up one week after treatment is started unless an earlier one is needed. This is to re-stain the eye to monitor the progress of healing. Pet owners must keep a close eye on injured eyes. If your pet’s eye seems more painful or if a pus-like discharge develops, rather see the vet sooner.

Most ulcers and erosions heal quickly while others require a bit more time. If there is minimal improvement after two weeks, the vet may advise on additional treatments or surgery. Depending on the case, you may be referred to a veterinary eye specialist.

Can eye drops have negative side effects?

There may be negative side effects, but this occurs rarely. If your pet is sensitive to an ingredient in the eye drops, you may see a marked response of swelling and irritation around the eye. If your pet’s eye appears more angry and painful after the eye drops than before, stop using them and speak to your veterinarian about an alternative.

Atropine eye drops if prescribed will cause the pupil to dilate in the eye in which it is applied. This is a normal and expected response. This also means that the eye is more sensitive to light and your pet may squint when in bright light.

You may notice that your pet salivates a bit more after application of eye drops, especially cats. This is because eye drops are bitter and may drain into the sinuses and sometimes into the back of the throat. This is not an allergic reaction, but rather the response to tasting the bitter eye drops.

If ever your pet keeps their eyes half or totally closed when not sleeping, get them to the vet sooner rather than later as a deep corneal ulcer can destroy the eye.



Corneal Ulcers in Dogs by Ernest Ward, DVM, Viewed on 29 September 2020.

Corneal Ulcers and Erosions in Dogs and Cats by Wendy Brooks, DVM, DABVP, reviewed 10 Oct 2018, viewed on 29 September 2020.

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