Glaucoma Surgery (Trabeculectomy)

Primary open angle glaucoma

Open angle glaucoma is the most common form of glaucoma in the UK affecting 1 in 50 adults over the age of 40. Although the drainage angle is open, there is microscopic damage to the trabecular meshwork within the eye, which means the fluid does not properly drain out of the eye. The eye pressure slowly rises, and although it doesn’t cause symptoms in the patient, the optic nerve is slowly being damaged. Damage to the optic nerve results in visual field loss – but you may not be aware of this, since the field loss in one eye may be compensated by the other eye, ‘filling in’ the loss in the visual field. This means that some patients don’t realise they have a problem until extensive damage has occurred. This is why glaucoma is sometimes known as the ‘silent thief of sight’, and is the reason why it’s very important to diagnose and treat glaucoma early.

Primary angle closure glaucoma

In primary angle closure glaucoma, the drainage angle in the eye is ‘occludable’. This means that the aqueous fluid cannot drain through the trabecular meshwork. Since the fluid cannot drain, the pressure in the eye rises. This can happen very quickly, resulting in a very high intraocular pressure and, usually, pain in the eye. The eye can also become red and vision blurred, with halos appearing around bright lights. The pain can be so bad that it causes nausea and vomiting. This condition is known as acute angle closure. It can result in permanent vision loss, in a very short space of time, especially if treatment is delayed. However, if the angle closure attack is treated promptly, the vision recovers.

Sub acute angle closure glaucoma

Sub acute angle closure attacks occur when patients experience mild instances of raised pressure, resulting in blurring of vision, some pain and redness. This then resolves. But if you do experience these symptoms, you should get yourself checked immediately. A more chronic, or slow-developing form of the disease is primary angle closure glaucoma (see above). This is where the intraocular pressure rises to a level that causes damage to the optic nerve but without any noticeable symptoms. The aim of treatment for this condition is to lower the intraocular pressure and open the drainage angle.

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Normal tension glaucoma

In this condition, the intraocular pressure remains within the normal range (between 10-20mmhg), however, there is still damage to the optic nerve. It is thought that poor blood flow to the optic nerve contributes to its damage. Patients with Raynaud’s Syndrome (a condition that affects blood circulation, causing cold hands and feet) and migraines have a high risk of normal tension glaucoma. This contributes to the theory that blood flow is important in normal tension glaucoma. If blood pressure is too low, it can result in worsening of the disease. For this reason, you may need to have your blood pressure control reviewed. Normal tension glaucoma is treated by lowering the intraocular pressure. This can be done with a number of techniques but usually selective laser trabeculoplasty (SLT) or pressure-lowering drops, in the first instance.

Ocular hypertension

In this condition, the intraocular pressure is raised but there is no damage to the optic nerve and no visual field loss. There is, therefore, no detectable glaucomatous damage. However, since patients with ocular hypertension have a raised intraocular pressure, they are at increased risk of the disease converting to glaucoma, especially if their cornea is thin and the IOP has been under-estimated. These patients may need to be treated to reduce their risk of developing glaucoma or monitored so they can start treatment as early as possible if glaucoma does develop.

Secondary glaucoma

With secondary glaucoma, the raised intraocular pressure does have a specific cause. This might be trauma to an eye, previous surgery, neovascular glaucoma (a condition where blood vessels grow in the drainage angle of the eye because of conditions like diabetic eye disease) or even certain medications like ones used to treat asthma or depression. Here, the glaucoma will need to be treated. The original cause of the glaucoma may need to be treated, too.

Congenital glaucoma

This is a rare condition where developmental abnormalities in the eye cause raised intraocular pressure. Patients may be aware that their vision has always been poor since childhood but may not realise they have an increased risk of further deterioration from glaucoma.