Glaucoma is an eye disease that involves progressive damage to the optic nerve through high pressure inside the eye.

It is a complex disease with various different subtypes. In South Africa primary open angle glaucoma is the commonest variety. Untreated it may lead to permanent loss of vision and blindness. Glaucoma is the 2nd most common cause of blindness worldwide.


The exact mechanism of open angle glaucoma is not perfectly understood yet, but with aging and associated genetic factors, the fluid that is created by the eye does not drain out of the eye as efficiently as it should due to microscopic blocking of the drainage meshwork in the eye. In closed angle glaucoma the drainage area is blocked by the iris and is usually due to an inherent anatomical predisposition to a narrow space for fluid drainage.


Mild to moderate glaucoma tends to have no symptoms. It is only in the late stages of the disease process that the affected person’s peripheral field of vision becomes progressively worse. Eventually the loss of field comes closer to the centre of vision and ultimately vision is lost completely if the glaucoma is not treated. There is often a strong family history of glaucoma and patients with a family history must ensure they
are screened for glaucoma by an ophthalmologist.


Glaucoma cannot be cured but can be controlled. By using eye drops we are able to lower the eye pressures and prevent on-going optic nerve damage. Drop treatment is adequate for the vast majority of glaucoma patients but in a small group the pressure cannot be controlled by drops alone and surgery is required.


There are several different surgical procedures to treat glaucoma but they all share the same principle: to drain fluid from the eye by making a small, controlled conduit between the inside of the eye and the space under the conjunctival membrane on the outside of the eye.

We favour the use of drainage implant devices:

The ExPress implant is a small titanium tube that holds open a drainage conduit in a controlled manner. Fluid drains from the inside of the eye and collects under the conjunctiva, forming a small blister or ‘bleb’. The fluid is then absorbed by the veins on the surface of the eye.

The Ahmed tube shunt is a silicone tube that leads to a plastic reservoir where the fluid collects. The reservoir is permanently attached to the eye, underneath the conjunctiva membrane and under the upper eyelid. The reservoir has a valve which prevents the pressure from dropping too low.

The Baerveldt drain is much the same as the Ahmed device but is favoured in certain clinical situations over the Ahmed. It does not have a valve and typically takes 6-8 weeks to start working.

The Xen Gel implant is a tiny flexible tube that creates a conduit between the anterior chamber of the eye and an area beneath the conjunctival membrane, external to the eye. It has the advantage of being minimally invasive and we have the ability to manipulate the effecicavy if the drain months later in the clinic.


Glaucoma drainage surgery can be done under local anaesthetic with conscious sedation or under general anaesthetic. The procedure takes about 15 to 45 minutes depending on the procedure and is done in the outpatient theatre complex. An overnight stay is not required and you will be able to go home after the operation.


The risk of vision loss from not having the surgery will be very significantly higher than the risk of vision loss from having the surgery. Glaucoma can be very serious and sight threatening and this surgery is intended to prevent vision loss and blindness. Broadly speaking, the risk of a serious complication with glaucoma drainage surgery is about 1 to 2 in a hundred. Significant complications are not common.

Some of the potential risks:

  • Cataract – the natural lens frequently becomes hazy following glaucoma surgery necessitating cataract surgery after a few years.
  • Hypotony – the eye is too soft after surgery. You may need to go back to theatre to tighten stitches.
  • Infection – the rate of a serious infection is about 1 in 500. These are always significant and treatment is required to prevent vision loss.
  • Haemorrhage – this is uncommon. Bleeding from within the eye due to low pressure.