Glaucoma in dogs refers to a group of diseases that affect the optic nerve

Optic nerve

The optic nerve, also called cranial nerve 2, transmits visual information from the retina to the brain. Derived from the embryonic retinal ganglion cell, a diverticulum located in the diencephalon, the optic nerve doesn't regenerate after transection.-Anatomy:The optic nerve is the second of...

 and involves a loss of retinal ganglion cells

Ganglion cell

A retinal ganglion cell is a type of neuron located near the inner surface of the retina of the eye. It receives visual information from photoreceptors via two intermediate neuron types: bipolar cells and amacrine cells...

 in a characteristic pattern. Raised intraocular pressure

Intraocular pressure

Intraocular pressure is the fluid pressure inside the eye. Tonometry is the method eye care professionals use to determine this. IOP is an important aspect in the evaluation of patients at risk from glaucoma...

 is a significant risk factor for developing glaucoma (above 22 mmHg or 2,933.1 Pa). Untreated glaucoma in dogs leads to permanent damage of the optic nerve

Optic nerve

The optic nerve, also called cranial nerve 2, transmits visual information from the retina to the brain. Derived from the embryonic retinal ganglion cell, a diverticulum located in the diencephalon, the optic nerve doesn't regenerate after transection.-Anatomy:The optic nerve is the second of...

 and resultant visual field

Visual field

The term visual field is sometimes used as a synonym to field of view, though they do not designate the same thing. The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments", while 'field of view' "refers to the physical...

 loss, which can progress to blindness

Blindness

Blindness is the condition of lacking visual perception due to physiological or neurological factors.Various scales have been developed to describe the extent of vision loss and define blindness...

.

Canine glaucoma can be divided roughly into two main categories, primary or secondary glaucoma

Glaucoma

Glaucoma is an eye disorder in which the optic nerve suffers damage, permanently damaging vision in the affected eye and progressing to complete blindness if untreated. It is often, but not always, associated with increased pressure of the fluid in the eye...

. In dogs, most forms of primary glaucoma are the result of a collapsed filtration angle, or closed angle glaucoma.

Clinical Signs

Dog glaucoma often goes unnoticed until it is in a more severe state. There are rarely any symptoms in the early stages of the disease

Disease

A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...

 so regular eye checks by qualified veterinary professionals are important. Dogs will sometimes rub the eye if it is painful. An eye

Eye

Eyes are organs that detect light and convert it into electro-chemical impulses in neurons. The simplest photoreceptors in conscious vision connect light to movement...

 affected with glaucoma

Glaucoma

Glaucoma is an eye disorder in which the optic nerve suffers damage, permanently damaging vision in the affected eye and progressing to complete blindness if untreated. It is often, but not always, associated with increased pressure of the fluid in the eye...

 may be red, swollen, sore, or become clouded in appearance.

Predisposed Breeds

Certain breeds are predisposed to getting glaucoma

Glaucoma

Glaucoma is an eye disorder in which the optic nerve suffers damage, permanently damaging vision in the affected eye and progressing to complete blindness if untreated. It is often, but not always, associated with increased pressure of the fluid in the eye...

. Primary glaucoma most commonly afflicts dogs at 3–7 years of age but can occur at any age. The disease is most frequently seen in cocker spaniels, many of the terrier breeds, Poodles, Beagles, chow-chows, jack russell terriers, bassett hounds and Dalmatians

Dalmatian (dog)

The Dalmatian is a breed of dog whose roots are often said to trace back to Dalmatia, a region of Croatia where the first illustrations of the dog have been found. The Dalmatian is noted for its unique black- or brown-spotted coat and was mainly used as a carriage dog in its early days...

. However, primary glaucoma has been identified in almost every breed

Breed

A breed is a group of domestic animals or plants with a homogeneous appearance, behavior, and other characteristics that distinguish it from other animals or plants of the same species. Despite the centrality of the idea of "breeds" to animal husbandry, there is no scientifically accepted...

 of dog

Dog

The domestic dog is a domesticated form of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in...

.

Diagnosis

Veterinarian

Veterinarian

A veterinary physician, colloquially called a vet, shortened from veterinarian or veterinary surgeon , is a professional who treats disease, disorder and injury in animals....

s employ three general methods: (1) tonometry

Tonometry

Tonometry is the procedure eye care professionals perform to determine the intraocular pressure , the fluid pressure inside the eye. It is an important test in the evaluation of patients at risk from glaucoma...

, (2) gonioscopy

Gonioscopy

Gonioscopy describes the use of a goniolens in conjunction with a slit lamp or operating microscope to gain a view of the iridocorneal angle, or the anatomical angle formed between the eye's cornea and iris...

, and (3) ophthalmoscopy. Tonometry measures the IOP with an instrument. Normal IOP

IOP

IOP is a three-letter acronym or initialism which may refer to:* Inanimate Objects Party, an absurdist political party at the Rensselaer Polytechnic Institute...

 in dogs can range between 12 and 25 mm Hg and the two eyes should be similar in pressure. Gonioscopy is a diagnostic procedure to examine the angle

Angle

In geometry, an angle is the figure formed by two rays sharing a common endpoint, called the vertex of the angle.Angles are usually presumed to be in a Euclidean plane with the circle taken for standard with regard to direction. In fact, an angle is frequently viewed as a measure of an circular arc...

 of the anterior chamber

Anterior chamber

The anterior chamber is the fluid-filled space inside the eye between the iris and the cornea's innermost surface, the endothelium. Aqueous humor is the fluid that fills the anterior chamber. Hyphema and glaucoma are two main pathologies in this area. In hyphema, blood fills the anterior chamber...

. Direct and indirect ophthalmoscopy is necessary to evaluate the retina

Retina

The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...

 and particularly the optic nerve

Optic nerve

The optic nerve, also called cranial nerve 2, transmits visual information from the retina to the brain. Derived from the embryonic retinal ganglion cell, a diverticulum located in the diencephalon, the optic nerve doesn't regenerate after transection.-Anatomy:The optic nerve is the second of...

.

Surgery

Treatment for dog glaucoma has several options, with surgery often being the most effective for long term management.

Laser Surgery

Laser surgery is often performed to selectively destroy the tissue, ciliary body

Ciliary body

The ciliary body is the circumferential tissue inside the eye composed of the ciliary muscle and ciliary processes. It is triangular in horizontal section and is coated by a double layer, the ciliary epithelium. This epithelium produces the aqueous humor. The inner layer is transparent and covers...

, in an effort to reduce aqueous fluid

Fluid

In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....

 production. Laser

Laser

A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...

 surgery

Surgery

Surgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, or to help improve bodily function or appearance.An act of performing surgery may be called a surgical...

 can also be combined with placement of a shunt.

Enucleation

The eyeball is removed during this procedure, often reserved for patients with end stage glaucoma.

Intraocular Evisceration & Implantation

The inner contents of the eye are removed and replaced with an implant. The outer portions of the eye remain.

Canine Specific Intra-Ocular Shunt: TR-ClarifEYE

TR-ClarifEYE is a new implant made of a new biomaterial, the STAR BioMaterial, which consists of silicone with a very precise homogenous pore size, a property which reduces fibrosis

Fibrosis

Fibrosis is the formation of excess fibrous connective tissue in an organ or tissue in a reparative or reactive process. This is as opposed to formation of fibrous tissue as a normal constituent of an organ or tissue...

 and improves tissue integration. The implant contains no valves and is placed completely within the eye without sutures. To date, it has demonstrated long term success (> 1yr) in a pilot study in medically refractory dogs with advanced glaucoma

Valved Shunts

There are also several different glaucoma drainage implants. These include the original Molteno implant (1966), the Baerveldt tube shunt, or the valved implants, such as the Ahmed glaucoma valve implant or the ExPress Mini Shunt and the later generation pressure ridge Molteno implants. These are indicated for glaucoma patients not responding to maximal medical therapy, with previous failed guarded filtering surgery (trabeculectomy). The flow tube is inserted into the anterior chamber of the eye and the plate is implanted underneath the conjunctiva to allow flow of aqueous fluid out of the eye into a chamber called a bleb.

• The first-generation Molteno and other non-valved implants sometimes require the ligation of the tube until the bleb formed is mildly fibrosed and water-tight This is done to reduce postoperative hypotony—sudden drops in postoperative intraocular pressure (IOP).
• Valved implants such as the Ahmed glaucoma valve attempt to control postoperative hypotony by using a mechanical valve.

The ongoing scarring over the conjunctival dissipation segment of the shunt may become too thick for the aqueous humor to filter through. This may require preventive measures using anti-fibrotic medication like 5-fluorouracil (5-FU) or mitomycin-C (during the procedure), or additional surgery. And for Glaucomatous painful Blind Eye and some cases of Glaucoma, Cyclocryotherapy for ciliary body ablation could be considered to be performed.

External links

• http://www.trbio.com TR BioSurgical, LLC Website.
• http://www.petglaucoma.com Pet Glaucoma Website.