A corneal ulcer is an open sore of the cornea, which is the transparent dome-shaped layer which covers the front of the eye.
The cornea protects the eye from dust, germs, and other debris, as well as reshaping and focusing light rays onto the retina; it consists of five layers.
- Bowman’s membrane
- Descemet’s membrane
Tears bathe the cornea to keep it nourished and prevent it from drying out.
Damage to the outer layer of the cornea due to scratches (corneal abrasion). Erosion of the cornea typically involves more than one layer and can occur for several reasons.
- Injury or trauma (such as rubbing an itchy eye, foreign body)
- Infection (fungal, bacterial or viral infection especially feline herpes)
- Chemical irritants
- Eyelid/eyelash disorders
- Dry eye (lack of tear production)
- Foreign body
Secondary bacterial infection can develop once the cornea has become damaged, which further complicates the problem. In severe cases, the ulcer can progress through the layers of the outer eye and cause the eyeball to rupture.
- Pain, due to the rich supply of nerves, the deeper the injury, the greater the pain
- Ocular discharge
- Sensitivity to light
- Excessive tear production (epiphora)
- Eyelid spasms (blepharospasm)
- Cloudiness of the cornea
The veterinarian will perform a physical examination and thorough ophthalmic (eye) evaluation. Large ulcers may be visible to the naked eye. Fluorescein stain may be necessary to detect small ulcers, this test involves placing a dark orange dye called fluorescein into the eye and using a penlight or special cobalt blue filtered light which can help to identify damage to the cornea.
It is also important for the veterinarian to determine the cause. If the cat is experiencing flu-like symptoms such as a runny nose, sneezing, fever, then a presumptive diagnosis of “cat flu” (herpes or calicivirus) can be made.
- Scratches will show up on the fluorescein stain.
- A Schirmer tear test will be necessary to check for dry eye.
The goal of treatment is to address the underlying cause and help the cornea heal by controlling inflammation, pain as well as prevent secondary infection.
This may include drops to stimulate the production of tears, supportive care and/or anti-fungal medications, surgery to correct eyelid abnormalities.
- Atropine is a medication which causes the pupil to dilate and helps relieve pain as spasms of the ciliary muscle (which controls the dilation and constriction of the pupil) cause pain in the already damaged cornea.
- Topical or ocular antiviral medications can be of help for cats with feline herpes, these include Trifluridine, Ganciclovir, Famciclovir, Idoxuridine and Vidarabine.
- Unfortunately, as the pupil is dilated, the eye becomes more sensitive to light; therefore, it will be necessary to provide access to a dark room the cat can retreat to.
- Antibiotics to treat or prevent bacterial infection.
- Serious corneal ulcers may need to be protected by suturing the eyelid shut (tarsorrhaphy) for several days.
- An Elizabethan collar will be necessary if the cat won’t leave the eye alone.
As the ulcer heals, you may notice red streaks in the eye (neovascularisation), this is blood vessels which have formed to help with the repair of the ulcer. They will eventually go away.