What is glaucoma?
Glaucoma refers to increased pressure within the eye.
Is it painful?
Yes. In humans glaucoma is described as a migraine-like pain. We assume it is also painful in our animals given the improvement in their demeanour following treatment.
What are the clinical signs?
- A red eye which may appear enlarged
- A blue or hazy appearance of the normally clear cornea
- A dilated pupil which is unresponsive to bright light
- Loss of vision
- Squinting
- Intolerance of bright light
- Lethargy and head-shyness
What is the cause?
The fluid produced within the eye is normally drained via the iridocorneal drainage angle. This sits around the outer edge of the iris inside the eye. In primary closed-angle glaucoma the number of drainage holes is reduced (goniodysgenesis) leading to a build up of fluid inside the eye and subsequently increased pressure.
Increased pressure is not only painful but it can irreversibly damage the nerves within the eye resulting in blindness.
Goniodysgenesis is an inherited condition that can occur in any breed, however a number of breeds are predisposed including Cocker and Springer Spaniels, Border Collies, Basset Hounds and Siberian Huskies for example.
How is it diagnosed?
The above clinical signs especially in a predisposed breed are strongly suggestive of primary glaucoma. Increased pressure inside the eye is confirmed by measuring the pressure using a device called a tonometer. A procedure called gonioscopy can be performed consciously in the well-behaved patient to directly visualise the drainage angle and confirm whether goniodysgenesis is present. Ocular ultrasonography can also be used to rule out causes of secondary glaucoma such as lens luxation or tumours inside the eye.
Can it be treated?
Primary glaucoma cannot be cured but can be managed with treatment which aims to prolong vision and comfort for as long as possible. If diagnosed and treated quickly vision can sometimes be restored. A combination of medical and surgical treatment is often required:
- Medical – Eye drops can be used initially to control the pressure and act either by reducing the amount of fluid being produced in the eye, or by creating alternative drainage channels. Often a combination of the two are used.
- Surgical – If the pressure cannot be controlled with eye drops alone surgical shunts can be placed within the eye to increase the drainage of fluid. Laser surgery can also be performed to reduce the amount of fluid being produced within the eye.
If the pressure remains elevated and the eye is blind despite management, removal of the eye will be recommended to maintain the welfare of the patient. If only one eye is glaucomatous at the time of initial presentation and goniodysgenesis is diagnosed, it is advisable to initiate treatment in the unaffected eye as both eyes usually develop glaucoma within a year of initial diagnosis.
