Eye problems are very common in cats; however, the causes and complications are a little different from in dogs, so in this blog we’ll look at cats’ eyes…
What is a scratched eye?
The front of a cat’s eye is called the cornea – this is the transparent window that they look out through! In technical terms, this is a specially organised part of the sclera (the white, outermost part of the eye); however, it is much more fragile. This is because, to maintain full transparency, the microscopic fibres that make up the tissue must all be aligned exactly in parallel. Anything that disrupts them, or causes fluid to build up inside, will potentially restrict the cat’s vision.
If the outer layer (a strip of conjunctiva, a form of skin tissue, but only a couple of cells thick) is damaged, these delicate fibres are exposed to the outside. This is called a corneal ulcer, and whatever causes it, the problem is the same – the damaged cornea starts to swell and fill with fluid as it becomes inflamed due to the damage. This tends to be very painful, so your cat will often hold the affected eye closed, or blink a lot; in addition, they may rub at it, and often it’ll produce abnormally large volumes of tears. This is actually a protective response – the cornea has no blood vessels (otherwise it couldn’t be transparent!) and the cells get all their nourishment from the tear film. To heal, they need extra fuel and nutrients, so more tears are produced to help get these to the damaged area.
The trouble is that, contrary to popular belief, tears aren’t actually very good at stopping infection. The conjunctival membrane is – but as soon as it’s damaged, bacteria start to set up home in the hole. As they grow, they eat away at the ulcer, making it bigger and bigger unless stopped. Sometimes, the cat’s own immune system will clear the infection, and the ulcer will heal rapidly on its own. Sometimes, the ulcer grows and grows until the eyeball ruptures. More often, the immune system and the bacteria stalemate each other, resulting in a sore eye and limited vision, that persists for a long time.
What can cause a corneal ulcer?
Well, trauma is one common cause – cats run through bushes and grass, and occasionally they don’t blink quite fast enough – even though the blink reflex is reportedly the fastest in the body!
The other common cause of injury is fighting – when cats fight, they really mean it, and they like nothing better than to scratch at each other’s eyes. Most of the really deep corneal lacerations we see are caused by other cats’ claws.
However, there is also a third cause, one that’s much more common in cats than in other pets – herpes virus. This is one of the main causes of Cat Flu, and as well as causing a snotty nose and sneezing, the virus attacks the corneas. The result is sore eyes and open sores on the cornea itself – a viral corneal ulcer.
What are the symptoms?
The classical symptoms are:
- Pain – there may not be any blood vessels in the cornea, but there are definitely nerves there! Cats with painful eyes usually rub at them, but unfortunately, this doesn’t help matters…
- Blepharospasm – the cat will often hold the affected eye tightly shut, to try and protect the damaged area.
- Lachrymation – crying (poor things…).
In addition, you may see a grey or cloudy stain on the front of the eye, caused by fluid in the cornea, and sometimes new blood vessels growing in from the edges of the eyes, to help the healing process.
How is it diagnosed?
Our vets will have a good look at the eye using a special instrument called an ophthalmoscope, which allows us to see and magnify the surface of the eye. If the eye is really sore, we may put some local anaesthetic drops in to numb it, helping us to see what’s going on.
Once we’ve had a good look, we’ll apply a dye, usually the orange fluorescein. This chemical turns green in the eye, and sticks only to exposed corneal tissue, not healthy conjunctiva – so the ulcer is highlighted in green. That means we can measure it and see how big it is!
What is the treatment?
Most corneal ulcers only need us to “tip the balance” – giving the cat’s immune system a helping hand will allow it to defeat the bacteria, and then the wound will heal. So, the first line treatment for most corneal ulcers is a course of antibiotic eye drops.
Occasionally, that isn’t enough – an ulcer that doesn’t want to heal is sometimes called an indolent ulcer. In dogs, this is routinely managed with a surgery called keratotomy – scratching the surface of the eye under anaesthesia stimulates the eye to heal itself. However, in cats, the most common cause of indolent ulcers is herpesvirus infection. This needs to be treated with antiviral medication – a course of aciclovir eyedrops (a human drug) is sometimes necessary.
Even if herpes isn’t the cause, there are risks to performing a keratotomy in cats. Some cats, especially Siamese, Persians, and Himalayans, are prone to developing a condition called Corneal Sequestration, where a section of cornea dies but remains stuck down. If this occurs, it can be surgically removed, but that means removing large amounts of otherwise healthy cornea, so it’s best avoided!
In the most serious ulcers, it may be necessary to provide the damaged part of the eye with additional protection and blood supply – in these cases, a tissue graft from the edge of the eye (called a pedicle flap) may be needed.
However it needs treating, though, most eye injuries can be managed with little or no long term problems – returning your cat to the eagle-eyed hunter they were before!