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Eyes: Corneal Ulcers

Article refereed by Drs Jeff Smith and Cameron Whittaker at the Animal Referral Hospital, Homebush, Sydney

A corneal ulcer describes an injury to the cornea which may or may not be infected.

Anatomy

The cornea is the clear tough part of the eye lying directly in front of the lens and pupil. It has a convex shape and its edge is attached 360 degrees to the white (sclera) of the eye. It is fed nutrients and kept lubricated and clean by normal tear production.

There is fluid behind the cornea pushing it outwards, giving it a convex shape. The space containing this fluid is called the anterior chamber.

The cornea is made of many layers of cells which are slowly replaced by new cells growing on the bottom layer. Older cells on the top layer naturally “wear off”

The cornea has to be clear. Otherwise, one would have trouble seeing out of the eye. In order to be clear, the cornea has no blood vessels within it. This is ok unless it is injured in some way. Whenever there is an injury in the body, blood vessels deliver “healing agents e.g. white blood cells, clotting products to get things repaired ASAP.

Eye ulcer 1Normal feline eyeCorneal ulcer








Causes

Injury

If the cornea is injured e.g. by a foreign body, chemical burn, it is very difficult for healing to take place because of the lack of blood vessels. If the wound becomes infected, bacteria can have a real “field day” as the corneal cells “taste nice” and there are no defences.

Dry Eye

Some pets can develop a problem where the eye stops making tears. When this happens the cornea dries out as it has lost its source of lubrication and nutrition.

Entropion

Some pets have eyelids which roll inwards instead of maintaining a nice straight edge. The hairs on the eyelid rub against the cornea and gradually wear away the cells creating an ulcer.

Symptoms

Cornel ulcers cause pain and the whole eyeball can become very inflamed. Often the pet squints and may try to rub the eye.
There may be a small area of “blueness” visible to the naked eye at the injury site.

Left untreated, corneal ulcers can rapidly enlarge and can even perforate the full thickness of the cornea. If this happens, the fluid in the anterior chamber leaks out and unless emergency surgery is performed, the patient can lose the eye.

Treatment

Depending on how deep the corneal ulcer is, treatment will vary.

1) Third eyelid flap

The third eyelid can be placed across an ulcerated cornea to protect it whilst it heals. Blood vessels on the inside surface of the third eyelid offer healing agents to the ulcer below.

2) Conjunctival graft

Deep aggressive corneal ulcers or injuries sometimes need a flap of conjunctiva (the loose tissue on the inside edge of the eyelids) stitched to the edges. This provides a good blood supply to the injury and gets things repaired quickly. When it has healed, the flap is trimmed off at its base leaving behind a small amount of scarring.

3) Grid Keratectomy

We often place a grid pattern around the ulcer and surrounding area using a sharp instrument to allow new corneal cells to run along and stick to the underlying surface. If this is not done, the ulcer may “fill up” and appear healed, but the new cells soon “slide off” as they have no “roots” to stay attached.

See also...
Corneal ulcer case
Dry eye