Glaucoma

What is glaucoma

The optic nerve is like a cable which connects the eye to the brain enabling us to see. Damage to the optic nerve can cause progressive irreversible sight loss and blindness. Often the damage arises because of raised pressure inside the eye and glaucoma is the name given to a group of eye diseases which damage the optic nerve in this way.

A healthy eye constantly produces fluid, aqueous humour which circulates inside the eye ball and drains into a sieve like meshwork, the trabecular meshwork inside the eye. From here the fluid enters the bloodstream. This fluid is different from the tears that lubricate the outside of the eye.

Types of glaucoma

In high pressure glaucoma the drain, or trabecular meshwork gets blocked and the pressure inside the eye rises.

There are many types of glaucoma, most are associated with raised pressure inside the eye, but sometimes the eye pressure is normal and the disease is caused by other mechanisms. 

Ocular hypertension  Additionally there are other people who have raised eye pressure but no apparent damage to the optic nerve. Although the raised eye pressure is a risk factor for glaucoma it doesnt always need treatment.

Primary open angle glaucoma. This is the most common type and its prevalence rises with increasing age so that 1 in 50 over the age of 40 years are affected and 1 in 20 over the age of 80 years.

Angle closure glaucoma. This is more common in certain eye types, so people with small eyes or those who are longsighted are more at risk

Secondary glaucomas. These are associated with specific eye conditions such as severe diabetic eye disease or inflammation inside the eye or deposition of abnormal material which blocks the drain inside the eye. They cause very high eye pressures and if not treated promptly can cause rapid sight loss.

Normal tension glaucoma. As described above this type is not associated with raised eye pressure and there are likely to be many mechanisms contributing such as poor circulation and genetic factors.

 

Treatment of glaucoma - eye drops

The treatment for people with glaucoma is to lower the eye pressure. This can be done with eye drops, laser or surgery.

Eye drops once started are usually continued indefinitely. They are commonly required once or twice a day and some people may need to use more than one bottle.

 

Treatment of glaucoma - laser

There are a variety of laser treatments for glaucoma and increasingly some types are being used as primary treatments to prevent or delay the need for eye drops

Trabeculectomy
Baerveldt glaucoma drainage tube
Xen stent magnified

Treatment of glaucoma - surgery

In most cases surgical treatments for glaucoma are reserved for when eye drops or laser treatments are not enough to control the eye pressure.

There are an increasing range of options. Among the procedures that are most effective is trabeculectomy in which a new drain is fashioned in the wall of the eyeball to let the fluid escape from inside the eye, bypassing the blocked natural drain. The modern version of this operation Safe Surgery Trabeculectomy is considered by most specialists to be the gold standard procedure in glaucoma.

In certain aggressive types of glaucoma trabeculectomy may not be enough to control the eye pressure. There are options to insert a new physical drain or valve into the eye which is less likely to fail. These glaucoma drainage devices are very effective. 

There are two main types types – those with a valve to prevent very low pressure and those without a valve. Both have their benefits depending on the specific situation in which they are used. 

An example of the valved tube is the Ahmed tube and the non valved variety the Baerveldt tube.

 

In recent years there has been alot of development in the  minimally invasive glaucoma procedures (MIGS). This term encompasses a variety of operations in which a small device or stent is inserted into the eye. This bypasses the area of blockage or opens up space for fluid to drain into and so lowers the eye pressure. 

The devices are tiny compared to the glaucoma drainage tubes above. Typically they are between 0.5mm to a few mm in size. Some like the istent are located completely inside the eye ball. Others drain fluid from inside the eye to the layer under the surface, like the Xen Stent.  

 Although less effective at lowering eye pressure compared to trabeculectomy, the advantages of a less invasive operation indicate a role in suitable patients not needing large reductions of eye pressure. 

Video of i stent insertion 

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