The most frequent reason for consultation in canine ophthalmology is certainly “the red eye” with the evocative name. It is not always a simple “conjunctivitis”. Indeed, many causes are at the origin of this red eye. Very often this redness will associate with pain with blinking of the eyelids, discharge from the eye, rubbing of the eye on the ground by the dog or with the help of its paw. We will tell you about the problem of red eye in dogs.
But these symptoms exist in a large number of eye pathologies and are not characteristic of any.
The eye is made up of the eyeball proper, embedded in a cavity, the orbit and maintained by 6 oculomotor muscles. It also has appendages, the most important being the lacrimal glands and the connective membrane (or 3rd eyelid). The whole will finally protect through two eyelids.
This redness, whether inflammatory or due to another cause, affects almost all eye structures.
Any wound, any trauma to the globe or its periphery can be the cause of bleeding and inflammatory reactions and therefore of redness.
We will point out the affections responsible for the “red eye” from the most superficial to the deepest areas.
Skin and eyelids
Without being a strictly ocular pathology one can observe cutaneous redness, sometimes accompanied by depilations all around the orbit. These are inflammatory, infectious – bacterial, viral or parasitic -, allergic, or dermatomycosis dermatoses.
The eyelids are also the seat of inflammation (blepharitis) but also of malpositions such as entropion. One or both eyelids curl inward. And, the eyelashes rub on the cornea (transparent membrane of the eye) and irritate it. The treatment is surgical and must be early under penalty of seeing the whole eye gradually deteriorate, from conjunctivitis to the corneal wound. Ectropion is an eversion of the eyelids outwards, revealing the conjunctiva which reacts. Less serious than entropion, its correction is also surgical.
Appendages of the eye
The tear glands secrete tears that hydrate the cornea and flow through the tear duct. They sometimes become infected (dacryoadenitis) but very rarely. On the other hand, their duct is frequently blocked by inflammation, following the presence of a foreign or secondary body with a morphological predisposition in dogs with a short muzzle (brachycephalic). The diagnosis consists of instillation of fluorescein (dye) in the eye. Sometimes it is necessary to clear the obstruction under anesthesia by probing the tear duct.
The Harder’s gland is an accessory lacrimal gland producing about 1/3 of the tears, and is located in the internal angle of the eye. This gland can dislocate and protrude at the level of the internal angle of the eye , like a small red mass of 1-2 cm. The treatment is surgical.
Connective membrane
Conjunctivitis is the most common eye disease causing the “red eye” symptom. It is congestion of the conjunctiva. A thin pink membrane that unites the cornea (bulbar part) to the inner edge of the eye. eyelids (palpebral part). The color of the conjunctiva varies from pink to red; its appearance can also modify (swelling, edema, ulcer,…). The most frequent causes of conjunctiva are allergies, or mechanical causes (irritation by dust, eyelashes or foreign bodies). The classic presentation is the sudden appearance of this conjunctivitis following the introduction of a abrasive spikelet of grasses within membrane folds. They also rarely manage to penetrate behind the eyeball. In that case,
There is a particular form of conjunctivitis: “follicular conjunctivitis”. It is a violent inflammation of the conjunctiva with the presence of numerous lymphoid follicles on the surface of the third eyelid. They appear following chronic exposure to allergens or inflammatory agents. Treatment may require debridement of the follicles associated with local corticosteroid therapy over the long term.
Conjunctivitis can also be infectious and therefore requires local anti-infective treatment.
A parasitic conjunctivitis is on the rise. Thélaziosis due to Thelazia callipaeda, a small nematode worm (round, unsegmented) laid in the conjunctiva by a fly. Treatment involves anthelmintics such as milbemycins and symptomatic treatment.
Cornea
The cornea, the outermost transparent part of the eye, can be the site of numerous inflammations (keratitis) at the origin of the red eye: keratitis can therefore be qualified as “dry”, “purulent”, “ infectious ”,“ traumatic ”,…
Keratoconjunctivitis sicca (KCS) affects both the cornea and the conjunctiva. It is secondary to a gradual deterioration in the functioning of the lacrimal glands, and therefore secondary to a deficit in tear production. It may diagnose using a Schirmer test to indirectly assess the amount of tears produced. Artificial tears will be an adjunct to anti-infective treatment. Treatment with cyclosporin may prescribe to try to recover lacrimal gland function
When the cornea has an altered surface, it is called a corneal ulcer. In 90% of cases, the origin of the ulcer is traumatic. This ulcer can be more or less deep and lead to a perforation of the cornea. The diagnosis is made by a fluorescein test. From acute development, the ulcer can become chronic, with a cornea which becomes cloudy, which is invaded by blood vessels giving it a reddish appearance. The treatment involves healing, analgesics and anti-infectives. If this is not enough, various surgical techniques will practice, sometimes going as far as transplantation.
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Breathing difficulties in dogs
Choroid
It is the pigmentary and vascular coat of the eyeball, between the retina -tunique nerve- and the sclera -tunique fibrous structure. . It is extended forward by the ciliary body which fixes the lens and secretes the aqueous humor and by the iris whose color is specific to each. Uveitis or choroiditis is the inflammation of this tunica which results in pain, redness, miosis (pupillary narrowing) and a cloudy appearance inside the eye.
Iritis or anterior uveitis is an isolated inflammation of the iris that shows the same symptoms. Sometimes blood collects between the iris and the conjunctiva (hyphema), a sign of the violence of the inflammation. If the iris and the ciliary body are affected it is called iridocyclitis.
The treatments are symptomatic: fight against pain and inflammation.
Glaucoma
Glaucoma is a complex pathology of the eye, which by different mechanisms increases the pressure in the eye (IOP or blood pressure). It is a serious disease requiring a rapid consultation and an adapted and well-managed treatment otherwise the evolution leads to blindness and dilation of the organ. It causes a sharp pain, a dilated pupil (mydriasis) and a very particular redness. The sclera vessels will swell and appear in high relief when usually they are almost invisible. This tension gives a red appearance different from an inflammation. The treatment calls for specific eye drops often associated with general drugs and if this is not enough for various surgeries.
Finally, a violent trauma or complications of glaucoma or anterior uveitis can cause a dislocation of the lens with a characteristic appearance and which also causes pain and redness. The treatment is surgical.
In dogs, “red eye” is therefore not a disease, but a symptom of several benign or serious pathologies. To treat them effectively, it is necessary to make a precise diagnosis. And, therefore consult quickly and above all, avoid self-medication.