Keratitis in Dogs

Our furry friend's eye can suffer from a wide variety of conditions, believe it or not. There are several causes that can lead to these disorders. Today, in this article, we'll talk about keratitis, inflammation of the cornea.

At Soyunperro we'll explain what keratitis is, what conditions can cause it, the types of it, as well as the appropriate treatment. Let's get to it.

What Is Keratitis?

Keratitis is defined as inflammation of the cornea (the outermost layer surrounding the eyeball). The cornea as such should be smooth, shiny, transparent, and avascular (without blood vessels). In fact, it's transparent thanks to its lack of blood vessels and pigments.

Its curvature and transparency allow it to perform an essential function in light refraction and transmission. To better understand the conditions affecting our pet's cornea, we should know it has four layers: epithelium and basement membrane, stroma, Descemet's membrane, and endothelium.

It's worth noting that changes that wouldn't matter in other tissues become significant in the cornea, causing disturbances in its transparency, which interferes with visual function.

Symptoms in Dogs With Keratitis

The clinical signs characteristic of painful corneal processes are: protrusion of the nictitating membrane (or third eyelid), epiphora (tearing), and photophobia (excessive light sensitivity). Besides these, the more specific clinical signs of keratitis are:

• Loss of corneal transparency (from cell infiltration).
• Areas of edema (imbalance in corneal hydration).
• Formation of new blood vessels. This can be superficial or deep, telling us how extensive the lesion is.
• Corneal pigmentation from cell infiltration (migration of melanocytes due to corneal damage). It appears as a grayish-white granular cloudiness.
• Visual deficit when the keratitis is very severe.

Causes

The causes of keratitis are very numerous, and it would take a lot of space to detail each one. Generally, they can be the result of primary corneal problems or secondary ones following irritating factors on the cornea, such as: entropion (the eyelid itself folding into the cornea), foreign bodies, gases, etc.

When there's no identified factor causing the keratitis, its depth needs to be assessed (superficial or deep), and whether it's associated with ulcers or immune-mediated factors (the immune system itself attacking the body). This will determine the appropriate treatment.

Next, we'll look at the types of keratitis that exist and learn about their causes.

Types of Keratitis

1. Non-ulcerative superficial keratitis. This can be caused by microorganisms, autoimmune inflammation, entropion, foreign bodies, external physical or chemical agents, or a deficiency in tear production.
2. Immune-mediated superficial keratitis. This is bilateral keratitis (in both eyes), induced by ultraviolet radiation from the sun, mainly affecting breeds such as the German Shepherd and its crosses, although it can occur in others too. It's characterized by the appearance of lymphocytes (white blood cells), plasma cells, and superficial vascularization that gradually cover the cornea, affecting vision.
3. Ulcerative keratitis. This is characterized by loss of the corneal epithelium, and will be superficial or deep depending on which layers are affected. Ulcers cause pain, which shows up through the symptoms first described in this article, so it's advisable to see the vet to relieve our pet's discomfort.

Likewise, superficial ulcers can be caused by physical agents (entropion, trauma…), infectious agents (viruses and bacteria), corneal drying, and degenerative processes.

Deep ulcers are usually the result of a secondary bacterial infection progressing on a superficial ulcer, or from severe trauma. The appearance of these ulcers, contaminated by bacteria such as Streptococcus and Pseudomonas, is usually yellowish-gray. These require aggressive medical treatment.

Treatment

Treatment will depend on the type of keratitis our pet has. So, we'll group it according to the types described above:

1. Non-ulcerative superficial keratitis: treatment should be aimed at treating the cause. In addition, it will be paired with symptomatic treatment using antibiotic ointments, as well as corticosteroid ointment (as long as there's no associated ulcer).
2. Chronic immune-mediated superficial keratitis: topical application of a corticosteroid ointment (dexamethasone) until the inflammation and vessel formation disappear. Cyclosporine can also be given. If there's mucus/pus, antibiotics should also be given during the first week.
3. Ulcerative keratitis. The goal will be to regenerate the corneal epithelium that's suffered ulceration. So, the primary cause will need to be treated. Broad-spectrum topical antibiotics (neomycin-polymyxin, chloramphenicol) will be given as eye drops. If there's pain, cycloplegics (atropine) will be applied.

This process (depending on the ulcer) can take up to a month and a half to heal. In case of complications, the vet will consider surgical debridement. All of these need veterinary treatment and won't be cured with eye drops chosen by the owner or with chamomile.