Just with his particularly expressive eyes, your dog will tell you about his love, excitement, sadness, apprehension or a whole host of other emotions.
However, if he has problems with his eyes, he will certainly not be able to communicate his emotions as well; he may even lose his sight. It’s important that you can recognise your dog’s eye conditions very quickly because if the vet intervenes early, he will often be able to make the best possible recovery.
Structure of the eye of the dog
To be able to identify an eye problem in a dog, it is essential to know the very particular structure of his eye.
Your dog’s eye, like that of most mammals, is shaped like a globe and contains two liquid-filled cavities separated by the lens: the first, itself divided into two chambers, anterior and posterior, contains the aqueous humor; the second (or vitreous chamber) contains a gelatinous structure, the vitreous body. The crystalline lens that separates them is a lens that converges the light beams coming from the outside onto the retina, located at the back of the eye.
The retina contains the photoreceptors that enable vision. At the front, the eye is covered by the cornea, a transparent surface layer that protects the internal structures of the eye and directs light rays onto the crystalline lens. The eye also has a pupil (black) in the centre of a coloured iris. The eye muscles, which are very numerous, are used to mobilize the eyeball in different directions, contract or dilate the pupil, and modify the curvature of the crystalline lens to adapt the amount of light reaching the retina.
The dog’s eye has three eyelids: a lower and an upper one (like us), as well as a third well developed eyelid called the nictitating membrane. Located in the lower part of the inner corner of the eye, between the lower eyelid and the eyeball, it protects the latter and facilitates the removal of superficial foreign bodies.
It also contains a gland that contributes about 30 percent of the water phase of your dog’s tear film.
Normally the nictitating membrane is invisible, hidden under the lower eyelid, but it becomes apparent if there is a problem – this is known as the procidence of the nictitating membrane. It can be seen on one or both eyes. So it’s important to familiarize yourself with the anatomy of your dog’s eye and to be aware of where its nictitating membrane is located. Here are some common eye conditions:
Dislocation (or prolapse) of the lacrimal gland of the nictitating membrane (called the “nictitating gland”)
This specific affection of the nictitating membrane is characterized by the appearance of a swollen red/pink mass, the size of a hazelnut (hence its English nickname: cherry eye!). This mass corresponds to the displacement of the nictitating gland which, when inflamed, comes out of its lodge.
The nictitating membrane can be visible, in a completely normal way, when the dog is sleeping or has just been operated on and is in the awakening phase of the anaesthesia. However, if his nictitating gland is dislocated, you will notice a red lump protruding from the edge of the nictitating membrane, first intermittently and then eventually permanently. The dislocation may affect one or both eyes and is most common in young dogs (6 months to 2 years of age).
It may or may not be accompanied by conjunctivitis. There is no way to avoid its appearance because its cause is not known with certainty and some breeds seem predisposed (beagle, French or English bulldogs among others).
As a result, as soon as you notice the first symptoms, contact your veterinarian quickly. to set up a treatment. Intermittent dislocation can be relieved with anti-inflammatory eye drops. If it is permanent, it requires surgical treatment (repositioning of the gland), as the inflamed, oversized nictitating gland eventually irritates the conjunctiva and causes discomfort to your dog.
Inflammation of the conjunctiva is a very common condition in dogs.and can have many causes (allergies, bacterial or viral infections, irritations). In conjunctivitis, the eye is red and the tissue around the cornea is swollen (oedema). There is also discharge from the eye and a slight pain in the eye (your dog often keeps his eyes closed or rubs them).
Because of its many causes, some of which are infectious, you should not wait to consult your veterinarian who will do the necessary examinations to find the origin of the inflammation and implement the appropriate treatment, for example:
- by removing the source of irritation (misplaced eyelashes, foreign body, etc.) and administering eye drops to calm the pain locally
- prescribing antibiotics and eye washings in case of infection
- or by prescribing an allergy treatment.
This is excessive tear flow (your dog cries all the time!). The transparent tears that flow out can eventually turn wet hairs brown/rust or give them a bad smell. Epiphora accompanies many conditions that lead to excessive tear secretion (misplaced eyelashes, conjunctivitis, corneal ulcers) or block the flow of tears (blocked tear ducts among other things).
The very small dog breeds (miniature or toy) seem predisposed to often due to poor tear drainage. Other dogs may have their eyelids curl inward (entropion), causing the eyelashes to irritate the cornea (hypersecretion) while the curl obstructs the lacrimal drainage system. Surgery is often required to improve tear drainage and correct the position of the eyelids.
Your veterinarian will carry out the necessary tests to find the cause of the epiphora and offer you an appropriate treatment.
Here it is the opposite: dry eye, or keratoconjunctivitis dry, is linked to an insufficiency of tears lubricating the cornea and conjunctiva. If left untreated, your pet can go blind.
A dry eye often looks like a recurrent conjunctivitis or a persistent infection: mucous discharge (or purulent) sticking to the eyelids, dry nose, red and painful eye and loss of corneal transparency (slightly white-blue colour, dull eye) with or without visible ulcer.
Dry eyes are often caused by an autoimmune reaction, as your dog’s immune system mistakenly destroys the tear gland over time. However, other causes are also possible: ageing, infectious or hormonal diseases, side effects of certain drugs, trauma…
The diagnosis is based on the measurement of tear production on a strip (Schirmer test) which is completely painless and easy to do. The treatment is long. Its aim is to restore tear production by means of ointments applied twice a day and to treat the specific cause (e.g. eye drops or antibiotic ointments). Supportive treatments based on artificial tears can be added.
Glaucoma develops when there is an imbalance between the normal production of aqueous humor (liquid that fills the posterior and anterior chambers of the eye) and its evacuation which becomes insufficient. Its quantity increases and raises the intra-ocular pressure (IOP) to a level incompatible with good ocular health (the increase in IOP eventually leads to degeneration of the optic nerve and retina).
Glaucoma is painful and is often accompanied by vision loss. There is dilatation of the pupil (the pupil diameter of the two eyes may not be the same), redness of the eye or dilatation of the vessels in the white part of the eye (the sclera). One or both eyes may also appear larger and protruding due to the increase in volume.
The (sometimes intense) pain can cause your dog to keep his eyes partially closed or squinted, rub his eyes, or he may become depressed, lose his appetite or even stop responding to your calls. If your dog shows any of these signs of glaucoma you should consult your vet immediately (it’s an absolute eye emergency!) to prevent him from losing his sight.
The diagnosis of glaucoma is made by measuring IOP with a tonometer.
Your veterinarian will then suggest appropriate treatments to reduce IOP and maintain it within physiological values, either by applying eye drops or by surgery.
Cataract is a more or less extensive opacification of the crystalline lens that prevents the passage of light. The light can no longer reach the retina, resulting in varying degrees of vision loss, which can lead to blindness. Cataracts should not be confused with nuclear sclerosis (normal densification and hardening of the central part of the crystalline lens) which develops with age but does not prevent vision.
Cataracts are frequently hereditary and some breeds are predisposed (Australian shepherd, French bulldog, Staffordshire bull terrier, etc.). However, secondary cataracts also develop during diabetes, malnutrition, radiation, inflammation or trauma.
In diabetes, excess sugar in the blood also passes in large quantities into the aqueous humor and then enters by diffusion into the crystalline lens where it is broken down into sorbitol, which remains trapped in the crystalline lens. Attracted by the sorbitol, the water present in the aqueous humor enters by diffusion into the crystalline lens, causes it to swell and disorganizes its structure, hence the appearance of cataracts. Most diabetic dogs eventually develop cataracts.
A cataract lens appears whitish or bluish. This opacification, which can be easily seen by looking at your dog’s eye, can become more pronounced to the point of total blindness. The development or stabilization of cataracts depends on several factors such as the type of cataract, breed, or the presence of other risk factors. If the visual decline is progressive, the dog compensates with its other senses (hearing or smell) and it is sometimes difficult to realise that it can no longer see.
He sometimes bumps or moves more slowly; he may also show unusual defensive reactions if he is startled or does not distinguish clearly who is approaching him.
Many dogs adapt to their cataract without treatment. However, cataract surgery, performed by veterinarians specializing in ophthalmology, can help them regain good vision. Speak to your vet so that he or she can examine your dog’s general condition and arrange the most appropriate treatment.
Nobody likes to see their pet suffer. If you notice your dog rubbing his eyes with his paws or rubbing his head on the floor, it may be one of the first signs of an eye problem.
It’s also a good idea to consult your vet as soon as your dog’s eye looks abnormal, as many diseases manifest themselves with identical symptoms but have very different origins or consequences. In the case of glaucoma, for example, an emergency consultation can save your pet’s vision.