The eyes of dogs and cats are vital organs that play a key role in how they interact with their environment. Due to their unique eye structure, dogs have a wider field of vision, spanning 240 degrees, compared to cats, who have a field of vision of 200 degrees, and humans, with a field of vision of 180 degrees. This enhanced vision is beneficial for their natural instincts and stems from their ancestral hunting behaviours. Although cats have a narrower field of vision compared to dogs, they are known for their exceptional night vision and ability to detect small movements. These traits are essential for their hunting instincts, allowing them to spot prey even in low light conditions. While the eyes of dogs and cats are finely tuned for their survival and natural instincts, they are not immune to a variety of eye problems.
Despite their advanced visual capabilities, dogs and cats are susceptible to various eye infections, which can be triggered by several factors including allergies, tumours, trauma, or underlying health conditions. These infections may be caused by bacteria, fungi, or viruses, each potentially leading to a range of eye problems, from mild irritation to more severe conditions such as conjunctivitis, corneal ulcers, or uveitis.
Conjunctivitis: A Common Eye Condition
Conjunctivitis is a common condition seen in both dogs and cats, characterised by inflammation of the conjunctiva. The conjunctiva is a mucous membrane which covers the white part of the eyeball and lines the eyelids. It contains a network of blood vessels, nerves, and lymphoid tissue, allowing it to react quickly to threats.1 Symptoms of conjunctivitis include discharge, squinting, excessive blinking, redness, and swelling around the eyes.
Conjunctivitis can be caused by a variety of factors, including bacterial, fungal, and viral infections as well as allergies, tumours, and traumas. It can result from other eye disorders such as corneal ulcers, uveitis, glaucoma as well as keratoconjunctivitis sicca (KCS). It is important to find out if conjunctivitis is primary or secondary to rule out any underlying conditions.
Conjunctival infections are common in cats due to the highly infectious feline herpes virus (FHV-1). Cats can experience both a viral and bacterial infection simultaneously, often requiring a combination of antibiotics and antivirals for treatment. Young kittens can have severe reactions to FHV-1, where their eyes become sealed shut from discharge, requiring the need to be opened to prevent damage or blindness. Kittens typically show other symptoms such as nasal discharge, sneezing, and coughing. Conjunctival infections can also result in chronic dry eye as well.
Cats are not the only ones susceptible to the herpes virus; dogs are also at risk of contracting CHV-1, and it can often be fatal in puppies. The virus spreads through direct contact between infected and non-infected dogs. In older dogs, CHV-1 can present with mild respiratory issues in addition to ocular problems. CHV-1 can cause a variety of eye issues in dogs, whether during a primary or recurrent infection. Conditions such as conjunctivitis, ulcerative keratitis, and nonulcerative keratitis are all linked to CHV-1.
Keratitis and Corneal Ulcers
Nonulcerative keratitis is the inflammation of the cornea, which can result from various factors such as reduced tear production, trauma, and infections (including bacterial, fungal, viral, and parasitic). In many cases, keratitis can progress to ulceration of the cornea known as a corneal ulcer. A corneal ulcer develops when the outer layer of the eye, the cornea, becomes damaged, resulting in a small indentation. This damage can be limited to the surface or extend into the deeper layers of the eye.
Pseudomonas, specifically pseudomonas aeruginosa is a common bacterium that can cause corneal ulcers in dogs and cats. Pseudomonas is considered an "opportunistic pathogen" that causes illness in various species, particularly those with weakened immune systems or pre-existing conditions.2 It can also develop as a secondary infection following a viral or other bacterial infection.
Redness and inflammation as well as discharge - which may be watery, clear, yellow or green-coloured - may be signs of a corneal ulcer. Blinking more than usual, light sensitivity, squinting, and rubbing or pawing at the eyes can also be symptoms. Both topical and systemic antibiotics may be prescribed to treat Pseudomonas. A bacterial culture may also be conducted to identify the specific bacteria, ensuring appropriate treatment.
Preventing pseudomonas is crucial. While it can be found in normal environments, it thrives in oxygen-poor atmospheres. It is commonly present in soil, water, on the skin, and in man-made environments. It is important to note that many antiseptics do not kill pseudomonas as well. Hygiene plays a crucial role in preventing pseudomonas infections. Using pet-specific products and staying vigilant about potential sources of infection such as water bowls, is essential for reducing the risk.
Uveitis: A Serious Eye Inflammation
Infections, including those caused by bacteria, viruses, and parasites can lead to a range of health issues in pets. One such condition is uveitis. Uveitis refers to the inflammation of the uvea, which is the middle layer of the eye, including the iris, ciliary body, and choroid. Symptoms may include redness, pain, squinting, rubbing at the eye, discharge, cloudy or hazy vision, changes in the pupils or iris, and reduced vision.
Leptospirosis is a common bacterial infection in canines that can affect multiple organs, including the eyes, leading to uveitis. Felines are also susceptible to leptospirosis and although it isn’t common to see it manifest as uveitis, it can happen. The bacteria can spread through the bloodstream to the eyes, causing uveitis, which results in symptoms such as squinting, cloudy eyes, and pain. Leptospirosis thrives in warm, wet environments. Infection usually occurs through contact with the urine of infected animals, such as rodents, other dogs, or even livestock.3 The most common way of infection is through urine-contaminated water as well as urine-contaminated soil.
Treatment focuses on managing inflammation and pain. Anti-inflammatory medications, topical treatments, and pain management may be prescribed. The primary goal is to prevent secondary complications, such as glaucoma, retinal detachment, lens luxation, or synechia. Preventive measures can help protect against canine leptospirosis, with the vaccine offering protection against the four most common strains of the disease.
Conclusion
The eyes of dogs and cats are not only essential for survival and everyday life, but they are also vulnerable to a variety of conditions that can negatively impact their vision and overall health. From common infections such as conjunctivitis to more serious issues such as corneal ulcers or uveitis, these problems may arise from various causes, including bacteria, viruses, or underlying health conditions. Recognising the symptoms early and seeking prompt veterinary care is crucial to prevent further damage and preserve their eyesight. With correct attention and care, many of these conditions may be prevented, ensuring that our furry companions continue to see the world clearly and comfortably.
References:
- Sandy Walsh, R. (2024, January 3). Diagnosing, treating, and managing causes of conjunctivitis in dogs and cats. Today’s Veterinary Practice. https://todaysveterinarypracti...
- U.S. National Library of Medicine. (n.d.). PMC Home. National Center for Biotechnology Information. https://pmc.ncbi.nlm.nih.gov/
- Canine leptospirosis. Cornell University College of Veterinary Medicine. (n.d.). http://www.vet.cornell.edu/dep...
Article written by Lauren Coldiron, Equine & Large Animal Inside Sales Representative at Millpledge Veterinary.
