Glaucoma - Breeders Newsletter January 2011 What every dog breeder should know! “The Glaucomas are a diverse group of diseases united by the fact th

Glaucoma - Breeders Newsletter January 2011

What every dog breeder should know!

“The Glaucomas are a diverse group of diseases united by the fact that the intraocular pressure (IOP) is too high to permit the optic nerve and the retina to function normally” Paul Miller, Veterinary Ophthalmologist 2008

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The aqueous humour (the fluid in the front of the eye) is continually produced and drained. It is produced behind the iris, circulates through the pupil and drains inside the eye at the periphery of the cornea in the iridocorneal angle (or drainage angle). The pressure in the eye will increase if there is an imbalance between production and drainage. No disease of overproduction has ever been documented.

In order for the IOP to increase the drainage angle must be compromised. This can be secondary to disease in the eye eg uveitis creating debris/ cells that block the drain, or primary- an inherited, congenital structural disorder in the eye.

Most dogs with primary glaucoma are born with an abnormal looking drainage angle (primary angle closed glaucoma). The angle may cope for a while but with wear and tear the drain will eventually fail creating glaucoma. This disease is poorly responsive to treatment and carries a poor prognosis.

Gonioscopy is a technique that allows us to examine the opening of the drainage angle. We can then grade the angle as to how normal the ligaments that span the top of the drain appear. Maldevelopment of these ligaments “goniodysgenesis” is a marker for the development of primary glaucoma.

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Normal pectinate ligaments

 
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Closed drainage angle

Gonioscopy can be performed as an option during the ACES examination (eye test). We recommend that it is performed in these breeds known to have a high incidence of primary glaucoma: Akita, Alaskan Malamute, American Cocker Spaniel, Australian Cattle Dog, Kelpies and Heelers, Basset Hounds, Beagles, Border Collies, Boston Terriers, Bouvier des Flandres, Brittany Spaniels, Bull Mastiffs, Chow Chows, English Cocker Spaniels, Flat Coat Retrievers, Fox Terriers (smooth and wire haired), Golden Retrievers, Hungarian Viszlas, Maltese, Petit Basset Griffon Vendeen, Poodles (all varieties), Samoyed, Shiba Inu, Siberian Husky, Welsh Springer Spaniel, Welsh Terriers.

Having an animal with poor drainage angle does not necessarily preclude it from breeding or showing. We know from work with Flat Coat Retrievers that dogs with less affected drainage angles are less likely to get glaucoma. If you mate a severely affected dog with an unaffected dog you are likely to get moderately affected pups. Mating a moderately affected dog to an unaffected dog breeds mildly affected pups, reducing the glaucoma risk each generation. This allows you to breed away from the trait quite rapidly. Knowing the gonioscopy status of your dogs allows you to make responsible choices when considering matings.

Glaucoma is a painful, blinding disease that primarily affects relatively young dogs. Screening of dogs to minimise this disease is therefore extremely desirable. At present there are no genetic tests for this disease.

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