The cornea is the clear, transparent, protective membrane that makes up the front of the eyeball. A corneal ulcer is an abnormal erosion on or through the corneal surface. Corneal ulcers can be superficial, affecting just the surface layer, or deeper, involving the entire thickness of a dog’s cornea. Ulcers often appear suddenly, and they can get rapidly worse. Leaving a corneal ulcer without veterinary treatment can result in serous eye damage and the loss of an eye.
There are three layers in the cornea, made up of specialised cells. The outermost layer is the epithelium, which is a very thin layer of cells. Below the epithelium is the stroma, which is the main supportive tissue of the cornea. Lastly the deepest layer is "Descemet's membrane".
Erosion of a few layers of the first layer the epithelium is called a corneal erosion or corneal abrasion. A corneal ulcer is deeper erosion through the entire epithelium and into the stroma. With a corneal ulcer, fluid accumulates in the stroma, giving a noted “cloudy” appearance to the cornea structure. If the erosion goes through the epithelium and stroma to the deepest level of Descemet's membrane, a descemetocele is formed. A descemetocele is a very serious condition. If this Descemet's membrane ruptures, the liquid inside the eyeball can leak out, and irreparable damage to the eye can occur.
Corneal ulcers are very painful. Most dogs rub the affected eye to try to relieve this intense pain. Symptoms of a corneal ulcer are a red, inflamed swollen looking eye, a closed eye or squinting, blinking excessively, a weepy eye, a cloudy eye, rubbing and scratching at the face and eye and avoiding bright lights.
Corneal ulcers can develop for many different reasons. Common causes include traumatic injuries, such as stick injuries and cat scratches. Chemical burns from irritant substances can also cause corneal ulceration, and Dogs with Dry Eye and Entropion (in-turning eyelids) can be predisposed. Also, some dogs develop corneal ulcers due to abnormal in growing eyelashes, or growths on their eyelids. Some bacterial, and viral infections and some other diseases can make dogs more susceptible to corneal ulcers. These include epithelial dystrophy (an inherited weakness of the cornea in some breeds, e.g., Boxers), Keratoconjunctivitis Sicca (Dry Eye) in which the cornea becomes dry due to a lack of tear production. Also, dogs with hormonal diseases such as Cushing’s disease, Diabetes, and Hypothyroidism can also predispose them to this. Short nosed breeds are at a much higher risk of eye ulcers because their eyes bulge forward and are much more exposed.
Corneal ulcers are not always visible without the use of specialist stains and equipment. Corneal ulcers are detected with the use of Ophthalmic examination stains, such as Fluorescein. The stain is placed on the affected cornea and will turn fluorescent green and adhere to any areas of ulceration, allowing the ulcer to become visible. Large ulcers may be readily visible, while tiny ulcers can be enhanced using specialist ophthalmic lights and filters.
Treatment depends on whether there is a corneal abrasion, corneal ulcer, or a descemetocele present. Refractory, non-healing ulcers may also require swabbing to check for resistant bacterial infections. Your vet may have to refer your dog to a specialist Veterinary Ophthalmologist for further examinations and surgery if the corneal ulcer is severe or non-healing. In certain cases, it may be necessary to perform surgery to remove dead or poorly healing layers of corneal tissue, or to perform a corneal graft.
Contact your vet if your dog is showing any of these symptoms, or, if you suspect they may have had any recent trauma to their eye area. Their eyes, just like ours, are precious and far too important to leave unattended.
Treating a corneal ulcer does incur costs. To ensure you can cover the costs of any unexpected Vet bills, do get good pet insurance for your dog as a puppy, or as soon as you acquire them, before signs of any potential illnesses start.