eye.jpg - Caption. [Optional]

Introduction to the Eye 

An eye is a delicate and complex organ made up of the cornea (the clear outer layer), the sclera (the white outer layer), the conjunctiva (the pink tissue around the eye), and the tear system that keeps the eyes moist and clean. The eye depends on a variety of specialized cells, vessels, and nerves that turn what your dog sees into signals that are sent to the brain. Because the eye is exposed to the environment, it can easily become irritated or infected.

How Eye Infections Occur

Eye infections occur when your dog's immune system recognizes an infectious agent, such as bacteria, fungus, or viruses, that has been introduced onto and thrives in the eye tissues. This can occur after a scratch or injury, or when dirt and debris become trapped in the eye. Infectious agents can also enter the eye through blood vessels.

Many systemic infections (affecting other parts of the body) may also cause inflammation and eye infections. If your dog has a weak immune system or underlying health problems, they may be more likely to develop eye infections. Sometimes conditions such as allergies or blocked tear ducts can also lead to infection.

Common Types of Eye Infections in Dogs: 

• Conjunctivitis (“pink eye”): Inflammation of the pink tissue around the eye (conjunctiva), causing redness and discharge. The purpose of the conjunctiva is to contribute to the tear film, immune function, and to help smooth the movement of the eye globe. When this mucous membrane becomes inflamed, the tissue appears red and swollen. When the goblet cells that produce the mucus component of the tear film go into overdrive, the eye discharge thickens. and the eye will have excessively thick, colored eye discharge. Follicles within the conjunctiva, important for immune function, may overproduce white blood cells that help the eye fight inflammation and infection.

• Corneal infections (keratitis or ulcers): A bacterial or fungal infection of the clear, outermost surface of the cornea can range from a microscopic scratch in the cornea to a deep infection with the risk of losing the eye. Regardless of size, infected corneal ulcers are commonly painful and, without appropriate treatment, can progress rapidly.

• Viral infections: Can be associated with a variety of systemic illnesses like canine distemper and herpesvirus. Like any organ, the eye requires blood vessels, so when distant infections enter the bloodstream, the affected blood may reach the eye. This is why a thorough eye exam is important for every physical exam. Symptoms can range from non-specific signs of inflammation to signature features of a specific virus.

• Fungal infections: Although less common, your pet may be exposed to infection in certain environments or after trauma. Similar to viral infections, evidence of a fungal infection of the eye may be the first sign of disease elsewhere in the body.

• Bacterial infections: When bacterial eye infections occur, they can cause a variety of signs, including a bloodshot appearance, a blue color change to the cornea, or eye discharge that could be watery or thick.

• The eyelids and tear system are composed of vital tissues that are responsible for the normal health and function of the eye. When there is an abnormality in any of these, whether it is a defect your pet is born with or acquired, this can increase the risk of eye infection. Keratoconjunctivitis sicca is a common condition known as dry eye, that presents with characteristic mucopurulent (pus) eye discharge. This condition can resemble an eye infection, so it must be ruled out in all cases.

Diagnosis

Ocular symptoms vary between patients, depending on the underlying cause. Watch for signs of ocular disease include squinting or holding the eye closed for more than 24 hours, a red eye (bloodshot, bleeding), a blue color change to the cornea, eye discharge, blindness, or rubbing the eye on objects / pawing at their faces more often than normal. If you see any of these signs, a prompt visit to your veterinarian is needed. Many eye infections can rapidly lead to catastrophic eye damage or can be the first sign of a serious body disease so recognizing early symptoms of eye disease is important.

Your veterinarian starts by closely examining your dog’s eyes. An ophthalmoscope is a specialized instrument used to examine the inner structures of the eye. They may use a special dye and light to check for scratches or ulcers on the cornea.

Samples from the eye may be collected to help determine the type of infection present. Surrounding structures like the eyelids and tear ducts are also checked. In some cases, additional tests, such as blood tests and imaging, are performed to rule out other systemic diseases that could be contributing to the infection. These diagnostics depend on your pet’s overall health and symptoms.

Treatment

Treatment depends on the cause and severity of the infection. Most infections with a bacterial component are treated with antibiotic eye drops or ointments. Viral infections, such as herpesvirus infections that usually cause conjunctivitis and corneal ulcers, are treated with antivirals. Some viral infections, such as canine distemper, which usually causes uveitis (inflammation of the middle layer of the eyeball), require supportive care while the body fights the virus. For infections affecting the entire body, the underlying cause has to be found and then treated systemically to see improvement in the eyes. Pain relief and anti-inflammatory medications may also be used. In more serious cases, especially with corneal ulcers, more intensive treatment or even surgery may be needed.

It’s very important to give all medications exactly as prescribed to avoid worsening the infection.

Ultimately, the two main goals of treatment are comfort and vision. Depending on the underlying cause, the treatment plan is tailored to achieve these goals.

Prognosis

The prognosis for eye infections in dogs can vary depending on how early the problem is found and how severe the infection is. Corneal infections generally have a guarded prognosis for saving the eye. However, the prognosis for uveitis is much more variable, from treatable to fatal disease, depending on the underlying cause. Some infections may clear up after two weeks of proper medication, such as Canine herpesvirus, when treated with two weeks of antiviral medication. However, more serious corneal infections may need longer treatment to allow blood vessels to grow in the eye to help clear the infection (neovascularization), usually takes five to six weeks to heal. Systemic infections may need at least four weeks of oral antibiotics. In some cases, surgery may be the treatment of choice. When left untreated, some cases can progress, leading to pain, permanent damage, and vision loss.

It is important that any abnormalities in the eye be assessed by your veterinarian immediately.