A corneal ulcer can be defined as a condition, in which the outer layer of the cornea gets damaged and lost. The most common reasons for this condition, are trauma, eye infections and exposure to chemicals. In case of dogs, corneal ulcer is considered a serious medical condition that may lead to loss of vision. Hence, early diagnosis and immediate treatment is absolutely necessary.
A dogs' cornea is made up of four layers - the outer epithelium, followed by the corneal stroma, the Descemet's membrane, and the innermost endothelium. The cornea is a transparent membrane, and in dogs, it is around one millimeter thick. This part of the eye does not have any blood vessel or pigmentation; and so, it is transparent in nature. The arrangement of collagen fibers also contribute to the transparency of the cornea. However, the cornea has nerves as well as pressure and pain receptors. The cornea is responsible for refracting light, thereby enabling the pet to focus on an object; and for protecting the inner layers of the eye.
Corneal Ulcer in Canines
The condition denotes cell loss in the corneal epithelium, due to various reasons. In some cases, the underlying corneal collagen may also be lost. Injury to the corneal epithelium is common in dogs and cats. In most cases, the lost cells are naturally replaced by new ones, and the ulcer heals fully. In some cases, either the new cells are not formed or the newly formed cells are weak enough to cause further injury or infection. Such corneal ulcers may allow microorganisms to enter the eye, which gets infected. Otherwise, the ulcer may spread to the deeper layers of the eye and result in eye rupture.
Corneal ulcers can be of two types - superficial and deep. While superficial ulcers involve a partial or total loss of the outer layer of the cornea, deep ulcers are characterized by loss of more than one half of the thickness of the cornea, as they extend through the stroma. Superficial ulcers take only a few days to heal, whereas the deep ones need more time. A deep corneal ulcer may leave a corneal scar, or may re-ulcerate or refuse to heal.
The healing process happens in two different ways. The surrounding epithelial cells shift to the affected part, and fill the space through rapid cell division. Another method is introduction of blood vessels from the conjunctiva to the affected part. In that case, white blood cells and fibroblasts produce scar tissue to cover the affected area. The first type of healing can be seen in superficial ulcers, and the second type occurs in deep ulcers.
Causes and Symptoms
Dogs are prone to corneal ulcers, as they indulge in activities that may cause scratches and injuries to the cornea. In dogs, the cornea may develop scratches, as they rub their paws on the face or fight with other animals. Even ingrown or misplaced eyelashes may cause such corneal scratches. Ulcers may also develop due to eye infections caused by viruses or bacteria; and exposure to chemicals, heat or smoke.
Dry eye or keratoconjunctivitis sicca (reduction in tear production) is another reason for corneal ulcers in dogs. Inadequate blink responses may also cause this condition. While breeds with protuberant eyes are more prone to develop corneal ulcers, the condition is seen in older dogs too. As the condition is painful, the symptoms include increased pawing or rubbing at the eye, squinting, redness, tearing, cloudy cornea, red or green mucus discharge from the eye, redness of the eyelids and the area surrounding the cornea, lethargy, and changes in normal dog behavior.
If your pet develops any of the symptoms mentioned above, consult the vet as early as possible. Usually, corneal ulcers are detected through direct observation, after application of fluorescein stain. Other diagnostic tests include Schirmer's test for detecting dry eyes, and tests to analyze facial nerve function, to detect facial nerve paralysis. If the underlying cause is eye infection; samples are collected and tested, in order to find out the particular infectious agent.
Usually, the condition is treated using pain medication and topical application of antibiotics. This treatment may be sufficient to heal superficial corneal ulcers, but deep ones may require suturing, conjunctival grafts or conjunctival flaps. In some cases, soft contact lenses are used, whereas some others have to undergo corneal transplant. The affected dog may be fitted with an e-collar, to prevent him from rubbing the eyes with paws. For severe corneal infections, oral antibiotics are also administered. Oral anti-inflammatory drugs are given, if there is inflammation inside the eye. However, topical application of corticosteroids and anesthetics is avoided, as these drugs can make the situation worse.
If left untreated, corneal ulcers may result in loss of vision. So, get the condition diagnosed and treated at the earliest.
Disclaimer: This article is for informational purposes only, and should not be used as a replacement for expert advice.