Red eye in dogs: conjunctivitis
Red eye in dogs is one of the many clinical signs that accompany conjunctivitis, a common problem in man’s best friend. It is caused by inflammation of the conjunctiva – a membrane that lines the white of the eye and inside of the eyelids. Breeds with more prominent eyes, such as Pekinese, Bulldogs and Pugs, are more likely to develop conjunctivitis.
Conjunctivitis in dogs: clinical signs
Red eye is one of the most apparent signs of conjunctivitis. The body directs more blood to the affected area to encourage the action of its natural defences, which adds to the irritation caused by the external agent and provokes reddening of the sclera.
Another classic sign of conjunctivitis is excessive tearing, which is a defensive response intended to lubricate the affected area and flush away the irritant.
Conjunctivitis is accompanied by eye pain, so dogs are constantly blinking, closing their eye (or eyes) or trying to paw at it. Palpebral oedema and hypersensitivity to light also occur, which is why dogs tend to squint their eyes in bright conditions.
Types, causes and treatment of conjunctivitis
- Allergic conjunctivitis
In this case the inflammation is caused by an allergic reaction, so it is not contagious. The main causes are insect bites or contact with an irritating plant. It may also occur when dogs come into contact with mites, pollen, cosmetics and household cleaning products.
This type of conjunctivitis has a good prognosis and usually resolves quickly. Eyes can be cleaned with saline solution and oral or injected steroidal anti-inflammatory drugs administered.
- Infectious conjunctivitis
Infectious conjunctivitis may have a viral or bacterial origin. Viral conditions spread and infect animals with relative ease. Infectious conjunctivitis is usually accompanied by tearing and crusty, gummy eyes.
A study1 of 30 dogs with conjunctivitis found that canine herpesvirus-1 (CHV-1) and canine adenovirus-2 (CAV-2) are the most common aetiological agents in conjunctivitis, although it can also be caused by viruses such as distemper, herpesvirus and parainfluenza.
Bacterial conjunctivitis is due to the growth of bacteria that come into contact with the dog’s eyes and start an infection. In this case, the ocular secretions usually take on a yellowish or greenish colour.
It is important to determine the cause of conjunctivitis so that the most appropriate treatment can be selected. For instance, if it is found to be bacterial conjunctivitis, then antibiotic therapy is indicated. A study conducted at the University of Zurich2 analysed the application of a technique involving corneal collagen cross-linking with riboflavin and UV-A radiation. This procedure increases the biomechanical stability of the cornea by inhibiting the enzymatic activity of collagenase and reducing the number of bonding sites. The process also generates free radicals that destroy the microorganisms inhabiting the corneal surface.
Note that if the infection is not controlled promptly and it manages to penetrate the intraocular structures, it can cause damage that could result in irreversible vision loss.
- Keratoconjunctivitis sicca
Also known as dry eye syndrome, it courses with chronic inflammation of the tear glands, cornea and conjunctiva. Basically, the patient’s eye produces fewer tears, which leads to dryness and damage to the cornea.
The lack of tear secretion may be the result of an idiopathic autoimmune reaction that destroys the tear gland and produces fibrous tissue. On the other hand, it could also be due to other diseases, such as distemper, neuropathy or chronic blepharitis.
The treatment of choice focuses on lubrication and the application of tear stimulants. Cyclosporine and tacrolimus are effective in dogs that still retain some tear-producing function, according to an analysis published in Veterinary Medicine.3 However, treatment must be followed for several months before the increase in tear production to become effective.
Finally, it is important to note that topical drugs are not usually recommended because the ocular region is very delicate and skin absorption is poor.
