Our eyesight is possibly one of the most precious senses we have, and that goes for your pet too. But one of the most common requests we have is for ‘over the counter’ medication for a ‘runny eye’.  Apart from regulations that restrict us from dispensing medicine without having properly examined a patient and diagnosed a problem, we wouldn’t want to run the risk of causing damage. If given the wrong treatment a simple eye infection could become a corneal ulcer. The occurrence of corneal ulcer is common, particularly in dogs and cats that are flat faced such as Pugs, French bulldogs, Persian cats etc.

What is a corneal ulcer?



To understand how a corneal ulcer occurs we need to take a quick look at the anatomy the eye.

As we can see in the diagram above the cornea is the transparent layer that forms the front of the eye.

The cornea itself has three distinct layers:


  • The outer epithelium
  • The stroma
  • The endothelium (inner most layer)

A corneal ulcer occurs when there is a break in the outer layer, the epithelium, of the cornea.

Symptoms you may see in your pet:

• Runny eye
• Squinting
• Sensitivity to light
• Yellowy green discharge
• Cloudy eye


Ulcers can occur for a variety of reasons such as:

• Trauma
• Foreign body
• Rubbing or pawing at the eye
• Eyelashes rubbing on the eye
• Entropion =eyelid rolling in – common in certain breeds
• Dry eyes – keratoconjunctivitis sicca
• Corneal endothelial degeneration
• Viral infections in cats – Feline Herpes Virus
• Uveitis
• Glaucoma
• Eyelid tumours
• Corneal endothelial degeneration


Corneal ulcers can be either complicated or uncomplicated depending on how well and how quickly they heal.

In the picture on the left the ulcer is severe and quite visible, but this is not always the case. 

The lesion can be deep or superficial depending on the initial cause of the problem and whether there is infection present.

Superficial ulcers may only be detected when stained. (See picture right)

Corneal ulcers are further classified as uncomplicated or complicated based on their healing.

Diagnosing a corneal ulcer.

With any eye problem a proper eye examination should be carried out by a Veterinarian in order to establish the cause and be given relevant treatment. As damage to the cornea is not always visible with the naked eye, the use of a stain (As seen in the picture above) to determine the presence or absence of an ulcer is critical to proper diagnosis.  The stain enables the Vet to see if an ulcer is present, how big it is and the extent of the ulceration.  If your vet is concerned, he/she may refer you to a Veterinary ophthalmologist, who will use specialised equipment (slit lamp biomicroscope) to magnify and inspect the eye during examination.

Specimens or swabs may be taken and sent to a laboratory for bacterial, fungal or viral culture and/or for cytological examination.


The treatment depends very much on the severity of an ulcer.

Superficial corneal ulcer – if only the outer layer of the cornea is damaged the ulcer is classified a being superficial.

Non-complicated – these are ulcers that are usually caused by trauma i.e.; injury /grass seed or some other temporary cause.

These ulcers are basically superficial wounds and heal quickly with the correct treatment, in a few days (3 to 5 days upwards to 14 days).

Deep corneal ulcer – these are severe ulcers , damage is caused not only to the outer epithelial layer but also to the middle layer (stroma). Infection is often present in these ulcers,  they usually start as superficial but progress to much deeper wounds if not treated.

A deep corneal ulcer can eventually lead to all three layers of the cornea being damaged – descemetocele – which can result in the complete rupture of the eye – this is consider a surgical emergency.

Complicated – these corneal ulcers are usually caused by an anatomic abnormality such as entropion (rolling in of the eyelid) and require surgical intervention of the cause in order to heal the ulcer.


The healing of complicated and deep corneal ulcers can be protracted as infection is often involved.

Ulcers are painful. Your pet may experience spasms of the internal muscles of the eye causing the pupil to constrict, the ulcer also exposes nerve endings making the eye sensitive and irritated.

Most ulcers are treated with topical drops or ointments that, depending on the cause and type of ulcer, will contain antibiotics, antifungals or antivirals, and will help alleviate muscle spasms.  Oral medication may also be administered.

A soft contact lens may be used to cover the ulcer or an Elizabethan collar used to stop your pet rubbing the eye. A surgical procedure such as a conjunctival graft or flap may need to be performed. Again to protect the eye and aid healing.

In a healthy eye, complicated, uncomplicated, and simple ulcers will heal well with the correct treatment and management.

However, pets with deep or infected lesions, if not dealt with seriously and aggressively, can risk losing sight or an entire eye to perforation or rupture. Therefore, they pose the risk for loss of vision or loss of the eye altogether.

If your pets eye is runny or it is rubbing an eye or squinting, please don’t hesitate book an appointment with your vet to get it checked out!

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