Glaucoma in dogsIn many of our senior dogs the eyesight slowly deteriorates with age. This normal development is part of the course of events. No need to frighten dog owners. Unfortunately, in addition to the usual signs of aging, eye diseases can also occur that seriously affect the vision of your favorite animal and sometimes even lead to blindness. Some of these conditions are referred to as "glaucoma" or "glaucoma" by doctors. This group of various eye diseases, which usually go unnoticed for a long time, is always accompanied by increased intraocular prere and disturbed function of the eye.
The term glaucoma was coined by Aristotle. He used it to describe the blue-green shimmering coloration that an inflamed iris gets due to increased intraocular prere.
Glaucoma – the clouded dog eye | Favorite animal
The dog's eye
In dogs, similar symptoms of disease of the eyes occur as in humans: Watery eyes (epiphora), conjunctivitis, eyelid disease (z.B. Eyelid margin tumors, sty – also known as hordeolum). Likewise, dogs can suffer from diseases of the cornea (z.B. acute injury or trauma – such as shepherd dog keratitis) suffer, or the lens may be affected (z.B. Opacity of the lens in cataract – also called cataract). But how are your eyes different from your protege's?? Dog's eyes are flatter and consist mainly of the light-sensitive retinal cells (rods and tapetum lucidum), so that the quadrupeds see well in the twilight.
Let us now imagine the eyeball as a kind of ball. Similar to the way the compressed air inside the ball is kept in shape by, for example, leather, the so-called bulbus (eyeball) also has an outer covering. It consists in front out of a transparent cornea as a protective layer. On the side facing away from the observer, more or less in the eye socket, a white sclera surrounds the bulbus. Exactly at the border of cornea and sclera the iris bulges inwards and with it the "peephole" into the world, more precisely the pupil.
Behind the iris is the ciliary body – also called the ray body – which holds the lens in position with muscles and fiber strands (zonula fibers) and controls the adjustment of the radius of curvature (accommodation). But it is also responsible for the production of aqueous humor. The fluid is released into the posterior chamber of the eye, filling the entire interior of the eyeball and thus supplying the inner structures of the eye, which are not supplied with blood, with electrolytes, amino acids, sugar and hyaluronic acid, among other things. Small side effect: The aqueous humor is even equipped with local defense cells (immunoglobulins).
The amount and the distribution of the aqueous humor determine the intraocular prere. If this prere is too high, this can have painful consequences and trigger different forms of glaucoma. Usually happens when the outflow of fluid into the venous vascular system is disturbed (a small part – about 15% – also drains as uveoscleral outflow through the vessels of the ciliary body and iris), or the distribution of aqueous humor is no longer possible.
Depending on the clinical picture, the prere can rise suddenly (acute) or develop slowly and thus become chronic. An acute occurrence leads to blindness within a few hours (glaucoma absolutum).
The space between the iris and the cornea is formed by the anterior chamber of the eye, at the corners of which the chamber angles are located. Normally, the aqueous humor flows out through the canal of Schlemm. If it is a primary glaucoma, it is due to a narrowed or malformed chamber angle (goniodysplasia).
Primary glaucoma is the result of a deformed chamber angle from birth. In this hereditary disease, the chamber angle suddenly closes at some point in life and the intraocular prere rises to dangerously high levels. Leading symptoms of glaucoma are a reddened eye, a wide and above all rigid pupil (does not react to light) and a high intraocular prere. Often dogs show this painful condition also non-specifically – for example, by often squinting their eyes shut. So act quickly if you observe this in your pet. It can be a harmless conjunctivitis, but you should be on the safe side. Primary glaucoma often occurs between three and seven years of age. Usually affects only one eye at first. The second one, however, will most likely become diseased sooner or later (within months or years). Breeds that have a pronounced susceptibility to primary glaucoma include the Siberian Husky, Maltese, Poodle, Bouvier des Flandres (Flanders Cattle Dog), American Cocker Spaniel, English Cocker Spaniel, Dachshund, Basset Hound, Alaskan Malamute, Chow Chow, Dalmatian, Entlebuch Mountain Dog, Samoyede, Shar Pei, and many terrier breeds.
Increased intraocular prere can also occur as a consequence of another disease – as a so-called secondary glaucoma. Here you will find some pre-existing conditions that can act as triggers:
– Tumor: Tumors can form in the area of the ciliary body and the iris, disturbing the outflow system and thus increasing the internal prere. – Inflammation: Due to a cataract or infectious disease, individual cells from the anterior chamber of the eye can settle in the chamber angle and block it. – bleeding in: released blood cells due to clotting disorders or trauma can also cause blockages at the chamber angle. – Lens luxation: Depending on the positioning, a displaced lens disturbs or interrupts the outflow of aqueous humor under certain circumstances. Since a luxated lens does not lie still, secondary glaucoma is also the most common and most feared complication of lens luxation. There are also certain breeds that have a hereditary tendency to premature tearing of the zonular fibers. If the unfixed lens becomes wedged in the pupil, a condition called pupillary block glaucoma results.
Australian Cattle Dog, German Hunting Terrier, Jack Russell Terrier and Yorkshire Terrier, for example, can suffer from glaucoma due to lens luxation as early as four to six years of age. If you call a representative of these breeds your protege, you should immediately consult your veterinarian in case of a painful, cloudy and/or red eye. Talk to him/her about a possible disease. A referral to a veterinary ophthalmology practice may be necessary.
Symptoms of glaucoma in dogs
In case of glaucoma, three characteristic symptoms can occur; therefore, one speaks of the so-called glaucoma trias. However, it is not said that all three signs of the disease always occur and the intensity is always the same. In addition, not all breeds and characters show identical reactions regarding the sensation of pain.
– Red eye due to congested episcleral (belonging to the episclera, the uppermost layer of the sclera) vessels – dilated and rigid pupil (myadisasis) – pain due to increased IOP (intraocular prere = intraocular prere). From an IOP of 30 mmHg (millimeters of mercury column) migraine-like headaches occur. dogs show this by withdrawing, hardly eating and sleeping a lot. In addition, the four-legged friends like to rub the eye to remove the alleged foreign body as a cause of pain. The intraocular prere of both eyes is also different by at least 20%.
In addition to the glaucoma trias, however, other symptoms may also occur:
– Hydrophthalmos (enlarged, protruding eyeball) – due to chronically increased prere the cornea and sclera are stretching. The stretching may in turn lead to tearing of the zonular fibers, which may result in lens luxation. – corneal opacity – increased IOP sometimes leads to water retention. These overlay the cornea. Deprive it of its transparency. – Blindness – fine structures in the eye cannot withstand elevated IOP and retinal cells die off.
Diagnosis and therapy of glaucoma
If glaucoma is suspected, the veterinarian measures the intraocular prere with a tonometer. Normal values for a healthy dog's eye are in the range of 10 and 20 mmHg (varying somewhat depending on the study and the measuring instrument used). Since primary glaucoma often causes disease in both eyes – although this does not have to happen at the same time – prere measurement is absolutely necessary even in the supposedly healthy eye. Finally, the slit lamp can be used to examine the interior of the eye. Control the position of the lens. Tumors, inflammations and hemorrhages are quickly detected with this method. If the disease is a primary glaucoma, the chamber angles may have to be checked under local anesthesia with a special gonioscopy lens.
If your pet suffers from glaucoma, it will first be given a medication in the veterinary practice to lower the prere in the eye. The medicamentous therapy approach takes effect by inhibiting the production of aqueous humor or by increasing the outflow. The intraocular prere should already show a lower value at the first control measurements after about 30 minutes. Ideally, this will result in a drop below 25 mmHg over a period of up to four hours. If acute glaucoma with high intraocular prere cannot be treated with medication, the anterior chamber of the eye must be punctured to relieve the prere. If necessary, a short sedation is required, because not all animal patients keep still during this treatment.
Unfortunately, owners of animal glaucoma patients often have to come to terms with the idea that only a surgical intervention can provide lasting relief. For example, in the case of lens displacement, tumors or a genetic occlusion of the aqueous humor outflow, only surgery on the diseased eye preserves vision or relieves the four-legged friend of pain in the long term. If your furry friend is already blinded by the diseased eye, you can also treat the eye with drops for the rest of his life, but in some cases the removal of the eye is the better alternative for your pet. Also in the case of a tumor the intervention should be definitive because of the risk of metastasis.
In surgical interventions, the veterinarian specialized in ophthalmology can destroy the ciliary body with cold probes or lasers, or increase the outflow of aqueous humor by inserting thin tubes. Often, however, removal of the diseased eye makes more sense, because dogs form too much inflammatory products (fibrin), these clog the shunt and the procedure does not work. The affected eye is a constant threat to the pet and removal provides relief and reduces stress (for example, constant visits to the veterinary practice). This is a terrible news for you, but your animal manages very well with one eye.
Glaucoma is one of the most serious eye diseases and can lead to irreversible damage or even blindness within a very short time – in the acute form there is a time window of 48 to 72 hours. A suspected glaucoma is always an emergency and should therefore be presented to a veterinary clinic for initial treatment, even on Sunday evening. The control can then again be done by an ophthalmologist. Use your acquired knowledge about symptoms and predisposing breeds to spare your darling a painful ordeal well prepared and to preserve his vision.