What are corneal ulcers?
Corneal ulcers occur when one or more of the layers of the cornea have been damaged and eroded away. They’re usually classified according to the depth of the damage. If only the epithelium is missing this is known as a ‘superficial ulcer’, but if the ulcer extends into the lower layers it is known as a ‘deep ulcer’.
While superficial ulcers are uncomfortable, the eye itself is not at the risk of rupturing unless further problems occur. When an ulcer deepens the eye becomes weak and can even perforate. Deep ulcers lead to visible indentations on the surface of the eye and are often associated with inflammation and bleeding within the eye.
What are the signs?
Signs of corneal ulcers usually include pain and discharge. Look for squinting, tears and a depressed appearance. You might be able to see a lesion on the surface of the eye.
If you suspect corneal damage, look for;
- loss of transparency
- dry appearance
- foreign bodies (hair, grass seed etc)
- lacerations or an irregular surface
How is a corneal ulcer diagnosed?
The fluorescein eye stain test is a simple, affordable and effective test available in all consultation rooms and is used to demonstrate the presence or absence of corneal ulcers. In the presence of a corneal epithelial defect, the dye rapidly diffuses into the corneal stroma. The yellow stain looks bright green whenever an epithelial defect is present and would certainly indicate a corneal ulcer.
Read our article on 5 diagnostic procedures to examine the eye >
Why do corneal ulcers develop?
- Injury - most ulcers happen as a result of an injury or traum A dog rushing through long grass can easily get a scratch to the eye. This is more likely to happen in dogs and cats with prominent eyes. Always look in the eye and under the eyelids for foreign bodies.
- Breed – Pugs, Pekingese and Persians seem to be more at risk due to the eyes being more exposed. All animals with exophthalmos should be checked regularly.
- Feline Herpes Virus infection – this is a common cause of ulceration in cats. The virus damages the corneal tissue.
- Reduced tear production – animals with ‘dry eye’ will produce insufficient tears. The reduced lubrication makes the eyes more vulnerable to damage.
- Entropion - an in-rolling of the eyelid will expose the cornea to damag
- Eyelid tumours – these may interfere with blinking.
- Mechanical – check the eye carefully for distichiae, ectopic cilia and trichiasis.
- Glaucoma - this occurs in many breeds of dogs, including the American Cocker Spaniel, Basset Hound, Shar Pei, Jack Russell Terrier, Shih Tzu, Siberian Husky and Elkhound. Primary glaucoma is rare in cats.
- Crystalline deposits – in older dogs you can get dystrophy of the cornea associated with calcium deposits.
Medical management – 7 ways to treat an ulcer
- Antibiotics – these are frequently used for routine ulcers, though it’s ideal to take a swab for culture and sensitivity testing to avoid contributing to antibiotic resistance. Fluoroquinolones, such as ofloxacin, are often used as a first choice. Ciprofloxacin is active against Pseudomonas spp. Systemic antibiotics may also be used. Many vets will also choose to prescribe topical fusidic acid ointment or gentamicin solution as both are licensed for use in dogs, cats and rabbits in the UK.
- Analgesia – corneal ulceration is painful, and even a superficial ulcer will cause discomfort and blepharospasm. NSAID’s, atropine, paracetamol (Pardale), tramadol and gabapentin can all be used to help manage the pain.
- Atropine – this is indicated if the pupil is small or if uveitis is present. The miosis can often be more intense with the axon reflex from superficial ulcers.
- Systemic anti-inflammatory therapy – inflammation need to be managed when uveitis is associated with the corneal ulceration. Oral meloxicam is suitable in both dogs, cats and rabbits. Avoid using topical NSAIDs because they have some potential to delay epithelialisation.
- Autogenous serum drops - collagenases from leukocytes and invading bacteria, digest corneal stroma and potentiate ulcer formation, which in some cases can result in a deep ulcer. Serum contains alpha-2 macroglobulin, which is a protease inhibitor. By applying serum drops into the eye, the enzymatic destruction of corneal stroma is stopped. Ideally place the drops every two to four hours.
- Hyaluronic acid – this helps to promote wound healing, reduce scarring, whilst at the same time provides cushioning, lubrication and maintains tissue hydration. It’s available as topical drops, and in the UK is known as Remend Corneal Gel.
- Avoid corticosteroids - these will invariably make the problem worse as they have been shown to increase the severity of keratitis when given in the absence of antibiotics. Corticosteroids can also contribute to corneal thinning, perforation, increased intraocular pressure and cataract development.
3 Surgical options
If an ulcer is deep or not healing as expected, surgery is often required. The aim is to place healthy tissue into the corneal defect. In most patients the healthy tissue is taken from the same eye and from an area adjacent to the corneal ulcer.
For deep ulceration with infection
1. Debride – the aim is to remove infective or necrotic tissue. This procedure will be painful, so it’s performed under an anaesthetic. Remove the loosely attached areas of epithelium (corneal debridement) using sterile cotton buds.
2. Pedicle graft – in some situation, the most appropriate approach to a deep ulcer is to perform a conjunctival pedicle graft. This is generally preferred to a third eyelid flap as it provides better support and protection to the cornea. It also helps to fill any stromal defects as well as allowing inspection of the wound and application of topical drops.
And for persistent non-healing ulcers?
Check for the accumulation of dead cells at the edge of the ulcer. These will delay healing and need to be removed. The area must be debrided to allow cells from the healthy corneal surface to migrate towards the ulcer and fill the eroded lesion. You might use all the treatments above, plus;
3. Grid keratotomy – this is often preferred to a punctate keratotomy as it’s easier to judge the depth of the grid lines compared to performing punctate marks.
Always find and treat the cause
Whatever treatment protocol you chose, remember that it is essential that the underlying cause is found and corrected.