When the white of a dog's eyes turn red, it's important to address the underlying cause considering that, left untreated, red eyes in dogs may persist and become more troublesome to resolve. What causes though the white of a dog's eyes to become red? Veterinarian Dr. Ivana Crnec discusses the anatomy of a dog's eye and then goes on to explain in detail several possible conditions known for causing blood-shot eyes in dogs, giving general info on accompanying symptoms and treatment.
A Lesson in Anatomy
Dogs’ eyes look similar to human eyes. They function similarly and therefore are susceptible to the some common problems. Anatomically speaking, the eye has several important structures:
The Orbit –this is the the bony socket in which the eyeball lays. It is formed by several different bones and contains blood vessels, nerves and muscles.
The Sclera – this is the white, outer covering of the eyeball. It is relatively tough and therefore has a protective role. Under normal circumstances, the sclera is glistening white with a small number of thin red blood vessels.
The Conjunctiva – this is the thin membrane that covers the sclera. It spreads from the edge of the cornea to the inside of the eyelid.
The Cornea –this is the clear dome on the eye’s surface. It is responsible for letting the light inside the eye. It is responsible for focusing the light.
The Iris –this is the colored and circular part of the eye. It is responsible for making the dog's pupil larger or smaller based on the amount of light entering the eye.
The Ciliary body – this is the part of the eye’s wall responsible for producing the fluid that fills the eye.
The Choroid – this is the middle layer of the eye.
The Pupil – this is the black area located in the middle of the eye.
The Lens – this is the transparent structure that allows light to pass through the eyeball to the retina.
The Retina – this part contains light-sensitive cells that translate the energy from the light waves into nerve impulses.
The Optic nerve – this part transmits the nerve impulses to the brain.
The Upper and lower eyelid – these are the skin folds that reflexively blink, cover and protect the eye.
The Nictitating membrane – unlike humans, dogs have an additional protective cover, popularly known as a third eyelid.
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The Lacrimal glands – these are the glands responsible for producing the watery portion of the tears.
The Meibomian glands – these are glands responsible for producing the oily portion of the tears.
Bloodshot Eyes in Dogs
As previously stated, under normal circumstances, the sclera should be glistening white. Its red blood vessels should be lightly present and relatively thin. A red or bloodshot sclera is an indicator of an eye issue. They eye issues that manifest in bloodshot sclera range in severity – from something as simple and easily treatable as an allergy to something as serious and complicated as glaucoma.
Eye issues, tend to progress really quickly and if left untreated can easily lead to blindness. Therefore, if your dog has bloodshot eyes, do not hesitate to make an appointment with your trusted vet. If necessary, your vet may refer you to a veterinary ophthalmologist.
To determine the cause of bloodshot eyes and initiate proper treatment strategy, the veterinary ophthalmologist will perform several tests, such as:
- Complete ophthalmologic exam – to check the different anatomical structures of the dog’s eyes. It is performed by using an ophtalmoscope (handheld device that illuminates and magnifies parts of the eye).
- Schirmer tear test – to test the tear production. It consists of a graded strip of sterile paper that is applied to the eye and used to soak the tears.
- Fluorescin stain test – to check for corneal scratches and injuries. It uses a sterile strip of paper that contains fluorescent dye. The dye stains the damaged corneal tissue, thereby highlighting the exact region and extent of injury.
- Tonometry – to determine the internal pressure of the dog’s eyes. It is performed by using a tonometer.
- Blood test – to check for underlying systemic medical issues that may lead to bloodshot eyes. While most eye problems are primary (originating in the eye) some start elsewhere and involve other systems. These problems are called secondary conditions.
What Causes the White of a Dog's Eyes to Turn Red?
The most common causes of bloodshot eyes in dogs include:
Allergies – some types of allergens irritate the sclera and eventually cause bloodshot eyes. The condition is commonly known as allergic conjunctivitis and it is also associated with sneezing and yellowish-green eye discharge. The treatment includes removing the allergens or using antihistamines and corticosteroids to control the allergies.
Conjunctivitis – this is the medical term that indicates inflammation of the conjunctiva. It is the most common eye disorder dog parents see. It can be caused by mechanical irritants, bacteria, viruses or parasites. The treatment usually includes flushing the eye with sterile saline eyewash and applying topical antibiotic ointments. If the causative agent is parasite, the treatment involves removing the parasite (in anesthetized dog) and then applying anti-parasitic solutions prepared specifically for the eye.
Keratoconjuctivitis sicca (KCS) – also known as dry eye syndrome, this condition occurs when the lacrimal glands fail to produce enough tears. The eyes become dry, inflamed and dull-looking. The treatment includes moistening and lubricating the affected eye by applying artificial tears several times per day.
Eye trauma or injury – blinking, squinting, avoiding light and pawing at the eyes usually indicates some sort of trauma, such as presence of a foreign object. Never try to remove a foreign body that has penetrated the eye. In cases of eye trauma or injuries, your main responsibilities are to prevent further damage (by using bandage or an Elizabethan collar) and seek immediate veterinary attention.
Corneal ulcers – dogs are highly prone to corneal scratches or abrasions. If the scratches are deeper, then we are talking about ulcers. Corneal ulcers are extremely painful. They are accompanied by squinting, excessive tear production, light over-sensitivity and inflammation of the eye’s white. More often than not, the only way to treat corneal ulcers is to have them surgically repaired.
Glaucoma – the increasing pressure of the fluid inside the eyeball causes a great deal of pain, a fixed stare and clouding of the eye. As the eye continues to bulge, tears stream out and blood vessels expand eventually resulting in bloodshot eyes. Based on the severity of the glaucoma, the treatment varies from using drugs that decrease the intraocular pressure to surgery.
Uveitis – is an inflammation of the iris, ciliary body and choroid. It can be caused by infections, toxins, high blood pressure, eye trauma, eye tumors and certain metabolic conditions. It manifests with severe pain, reddening of the eye, excessive squinting and photophobia. The treatment has two goals – inflammation management and pain control.
About the Author
Dr. Ivana Crnec is a graduate of the University Sv. Kliment Ohridski’s Faculty of Veterinary Medicine in Bitola, Republic of Macedonia.
She currently practices as a veterinarian in Bitola and is completing her postgraduate studies in the Pathology of Domestic Carnivores at the Faculty of Veterinary Medicine in Zagreb, Croatia.