Narrow Angle Glaucoma

Glaucoma is the name given to a group of eye diseases characterised by an increase in intraocular pressure, this causes pathological changes in the optic disk and visual field defects. It’s a very painful condition that leads to varying degrees of blindness and in its severest form can result in removal of the affected eye or even possibly euthanasia.

Glaucoma can at first be categorised as Primary where there is an increase in intraocular pressure taking place in an eye without previous disease or injury, and Secondary where an injury or prior disease/infection leads to the condition.

In the case of Primary Glaucoma we can assume it is congenital and inherited. This hereditary form of Glaucoma in dogs take the form of Narrow-Angle Glaucoma which is characterised by a shallow anterior chamber and a narrow angle in which filtration is compromised as a result of the iris blocking the angle and impairment of outflow of aqueous humor, leading to a painful build up of pressure within the eye.

There is a physical eye examination that assesses the structure of the eye and these angles. Gonioscopy is not part of the standard eye examination but can be carried out by an Ophthalmologist, on its own or at the same time as a standard eye examination. It’s quite an awkward test because it involves the dog having a local anaesthetic in the eye and then a large round lens placed on the eyeball for the Ophthalmologist to look through. It’s important that the dog stays as still as possible in order that the vet can carry out a full examination. It may be necessary to sedate any dog that won’t sit still.

It is important to note that Gonioscopy is not a test for Glaucoma, it is simply an examination of the eye to assess any predisposition for Narrow Angle Glaucoma. A dog that tests affected for Goniodysgenesis will not necessarily go on to develop Glaucoma, indeed many do not. Should a dog test as ‘affected’, it is important that it has regular eye examinations in future. Once a dog is tested ‘unaffected’, it will not need to be tested again.

While it is acknowledged that Narrow Angle Glaucoma is hereditary, the means of inheritance are not known.