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GLAUCOMA

The size and shape of the normal eye is maintained by intra-ocular pressure, (IOP). This is regulated by the amount of fluid within the eyeball.  Fluid is constantly  produced by a structure called the ciliary body.  In addition to producing this fluid, (called aqueous humour) the ciliary body contains the suspensory ligament which holds the lens in place.  Muscles in the ciliary body acting through the suspensory ligament, control the shape of the lens and thus the focusing ability of the lens.

Aqueous humour, continuously produced by the ciliary body contains nutrients and oxygen which are used by the structures within the eye.  The excess fluid is constantly drained from the eye between the cornea and the iris.  This area is called the drainage angle, or iridocorneal angle.

The pressure remains constant since the production and absorption of aqueous is equal.

What is glaucoma?

Glaucoma is an increase in IOP.  This is measured using an instrument called a tonometer.  The cause of glaucoma is always related to inadequate drainage of aqueous rather than its over production.   Glaucoma can be primary or secondary.

Primary glaucoma results in increased intra-ocular pressure in an otherwise healthy eye.  Some breeds are more prone than others.  It occurs due to anatomical abnormalities in the drainage angle which have been present from birth.  For example in narrow angle glaucoma there is a shallow anterior chamber which causes the iris to block the angle interfering with the filtration.  Abnormalities in the drainage angle (goniodysgenesis) can lead to a raised IOP in middle age.

Secondary glaucoma results in increased intra-ocular pressure due to disease or injury to the eye.  This is the most common type in both dogs and cats.  Causes include:

·Uveitis (inflammation), resulting in debris and scar tissue blocking the drainage angle, and severe intra-ocular infections

·Anterior dislocation of lens.  This falls forward and physically blocks the drainage angle or pupil such that fluid is trapped behind the dislocated lens

·Tumours which cause physical blockage due to their size

·Intra-ocular haemorrhage.  The blood clot can  prevent physical drainage

·Damage to the lens.  Lens proteins leaking into the eye as a result of a ruptured lens can cause a reaction which results in blockage of the drainage angle

How is glaucoma diagnosed?

The commonest signs noted by owners are:

·Ocular pain, your dog may keep the eye partially closed and initially start to rub at it.  He may shy away as you go to stroke this side of his head

·As the pressure increases a watery discharge will be noted and the dog becomes depressed

·Physical swelling of the eyeball becomes  obvious.  The white of the eye looks  red and engorged

·The cornea or clear part of the eye may become cloudy (usually blue-ish in colour)

·Blindness.   Since the increase in pressure will compromise the delicate blood vessels and nerves within the eye, blindness can occur very quickly.

All these signs can occur very suddenly with acute glaucoma.  In chronic glaucoma they develop more slowly. They may have been present for some time before your pet shows any signs of discomfort or alteration of  appearance or habits.

Veterinary diagnosis depends upon accurate pressure measurements, (tonometry)  and the internal  examination of the eye using special instruments.

Acute glaucoma is an emergency.   Sometimes specialist help and advice is necessary.

Treatment

Each case has to be treated on its merits.  Initially it is important to reduce the IOP as quickly as possible and for this special drugs will be prescribed.

It is also very important that we examine your pet fully and treat any underlying disease which may be responsible for the glaucoma.

Medical treatment  is seldom effective long term and often has to be combined with surgery.  Analgesics are  prescribed to control the pain and discomfort associated with the condition.

Veterinary ophthalmologists employ various surgical techniques to reduce intra-ocular drainage.  Should such a procedure be necessary, this will be carefully discussed with you.  In the meantime it is important that medication is carefully and conscientiously administered.  If you do have any difficulties, please call us without delay.