Title

Jas

Riley

Glaucoma

We would like to thank Charlotte Freeman BVM&S Cert VOphthal MRCVS of The Mount Veterinary Hospital,21 High Street, Wellington
Somerset TA21 8LD Tel. 01823 662286 for her input into this section.

Glaucoma is an elevation of the pressure within the eye as a result of increased fluid. If the fluid pressure cannot be reduced it can cause devastating and irreparable damage to the retina and optic nerve resulting in visual impairment. Complete blindness can occur with 24 hours if the pressure is extremely elevated or it can occur over weeks and months if the elevation is mild.
The definition of glaucoma also encompasses the progressive death of retinal ganglion cells and their associated axons.

Glaucoma in itself is not a term for a single disease entity but a group of related diseases caused by different but overlapping factors.

The glaucomas consist of 5 stages:
a) an initial event usually involving the pathways for the outflow of fluid within the eye
b) physical changes to the outflow pathway/drainage angle causing obstruction
c) elevated pressure within the eye that is too high for the blood to flow and nerve impulses to fire
d) retinal cell dysfunction with resulting optic nerve degeneration and nerve cell death
e)vision loss and blindness

Continuous elevations in Intraocular pressure (IOP) obviously cause rapid and permanent damage to the retinal cells and quickly lead to pain and blindness. However, intermittent spikes in the IOP also switch on damaging amino acids mainly glutamate in the retinal cells leading to progressive retinal cell death even when the IOP has returned to normal. Therefore the canine glaucomas are neurodegenerative diseases with elevations in the IOP being the principal risk factor.

Primary Glaucoma

Great Danes are one of the breeds that are most commonly affected. The aqueous outflow pathway in the eye needs to be open and functioning properly. In some breeds of dogs the ‘drainage’ angle (iridocorneal angle) can be abnormal. The trabecular meshwork acts like a ‘sieve’ and if access to this sieve is narrow, or there are few drainage holes or the drain behind the sieve isn’t working properly it can result in an increase in intraocular pressure. Where the fluid passes through the sieve it may not drain into the veins around the eye well and can then back up causing pressure in the eye to increase.

In terms of the BVA primary glaucoma, the defect within the aqueous drainage system called pectinate ligament dysplasia (dysplasia means abnormal development or growth)is classified as schedule B and is under investigation. Pectinate ligament dysplasia is also called goniodysgenesis and primary closed angle glaucoma PCAG. This means that primary glaucoma in the Great Dane is becoming a recognised condition by veterinary ophthalmologists.

Veterinary Opthalmology 2007 (the Bible for vets with an interest in ophthalmology) has written specifically about glaucoma in Great Danes and states that there is a significant relationship between drainage angle/iridocorneal angle abnormalities in the parents and the offspring. Therefore the BVA suggests “clear breed and line predispositions indicate a genetically determined cause”.

Secondary Glaucoma

By being termed secondary this means that something else is happening in the eye to cause glaucoma. Inflammation within the eye is the most common cause of secondary glaucoma and this inflammation is called uveitis. The term uveitis is a description of which part of the eye is affected by the inflammation.

Uveitis can be caused by:
• Infectious agents such as bacteria, fungi, algae, protozoa and other parasites
• Trauma both blunt and penetrating
• Immune mediated disease processes within the body (the body attacking itself)
• Cancers and tumours either within the eye or elsewhere in the body
• And from cataract formation leading to leaking of lens protein into the called lens induced uveitis
• If the lens moves into an abnormal position in the eye this can cause IOP due to blocking the normal flow of fluid within the eye.

Glaucoma is also a recognised complication of cataract surgery.

Hazel Evans describes how Jas lost an eye through trauma

Glaucoma is a moderate to extremely painful condition. Some dogs rub their eyes red because of the discomfort. With other dogs their eye may look cloudy due to the swelling of the cornea and they will be sensitive to light. The affected eye can seem larger or appear to bulge out.

Treatment must be started as soon as possible if your dog’s sight is to be saved.

Early diagnosis is obviously best and your vet can measure the pressure within the eye with a tonometer on a regular basis. Local anaesthetic drops are placed in your dog’s eye to enable the test to be performed.

Tracy Rowe tells the heartbreaking story of how her blue Dane Riley was diagnosed with glaucoma

Treatment of glaucoma is often unsatisfactory as damage already occurred cannot be reversed. Saving vision in an eye with glaucoma is only viable if it has been diagnosed early enough and properly treated where the pressure in the eye can be controlled. In many cases the eye should be removed. A dog that has had glaucoma in one eye needs to be checked regularly for signs of glaucoma in the other eye.

Though the mode of inheritance in Great Danes has not been established the veterinary profession advise us that Great Danes that have been diagnosed with Goniodysgenesis/Primary Glaucoma should not be used for breeding.

NOTE:

The BVA/KC/ISDS Eye Scheme currently has Great Danes on their SCHEDULE B – CONDITIONS UNDER INVESTIGATION for Goniodysgenesis/Primary Glaucoma.