What is Glaucoma?

We've all heard of Glaucoma, but what is it?

We've all heard of glaucoma, after all it's one of the 3 most common eye diseases (cataract, glaucoma and macula degeneration). But what is it? What does it do to your eyes and can it be treated?

This should really help to answer those questions.

Glaucoma is a disease of the optic nerve in the eye. The optic nerve becomes damaged by having a high pressure in the eyeball (usually - I'll explain that later). The high pressure in the eye damages the nerves and blood supply to the nerves, and that nerve damage means you loose the peripheral part of your vision - that is the vision around you, we call that your visual field. The biggest problem with normal glaucoma is that you can't feel it, you have no idea it's there as there has to be a lot of damage and peripheral vision lost before you'll notice it. There are no pain receptors in that part of the eye so you can't feel it happening. That's why we think there are around 63million people with glaucoma world wide but half of them don't know they have it. That is why regular eye examinations are so important. 

What makes glaucoma really tricky to understand is it's not just one thing. There are a few types of glaucoma (we refer to them as "the glaucomas"). These range from the more common "normal" glaucoma to, thankfully, more rare forms.

To understand glaucoma we need to know a little about the anatomy of the eyeball. We need to look at the front of the eyeball where the cornea (the transparent window at the front, that you can see the iris and the pupil through) meets the iris. We call this the angle. In this angle there are some drainage channels which will let the fluids and hence the pressure out of the eye. 

This lets us look at the first type of glaucoma - Primary Open Angle Glaucoma

Primary open angle glaucoma is where the angle where the cornea (the transparent window at the very front of the eye) and iris (the coloured bit), meet is nice and wide and open that means that those drainage channels are open and clear. Primary open angle glaucoma will usually have a high pressure in the eye and it's that high pressure that's going to cause damage to the nerves and therefore damage to the optic nerve and lose that peripheral vision. This is what we would see most of in practice and I would refer to as normal glaucoma. 

Open angle glaucoma is usually treated with just an eye drop and many people only need to use one drop every day depending on how they respond to the different types of drops available. If the pressure does not respond with eye drops, then there is an operation that can be performed which helps to relieve the pressure called a trabeculectomy where a drainage channel is created under the upper eye lid. 

Next Normal Tension Glaucoma

What makes glaucoma very confusing is that there is another type of glaucoma known as normal tension glaucoma and this means exactly what it says the tension or pressure in that eye is normal. This makes it a lot harder to find and diagnose this type of glaucoma but again treatment for this type of glaucoma is just the same as in normal open angle glaucoma. 

Secondary glaucoma

The third type of glaucoma that we want to look at is what we would call secondary glaucoma these are glaucomas that have happened after an eye injury or from the use of certain medications such as steroids, or as a complication of other eye diseases or disorders which have damaged the eye such as inflammation like uveitis. 

Finally, Acute or Angle Closure Glaucoma

The next form of glaucoma is luckily a lot rarer than the other forms. This form of glaucoma can be extremely painful, this is acute or angle closure glaucoma. It’s mainly due to the anatomy of the eye - that angle created where the cornea meets the iris, in angle closure glaucoma, that angle is too narrow - it's very narrow or closed off and this can have a devastating effect on the drainage channels and the pressure can rapidly increase in the eye to a point where it is incredibly painful. Treatment for acute glaucoma is usually to use a laser to put holes in the iris to relieve that pressure straight away. Acute glaucoma is also difficult to diagnose because people can have mild "attacks". It's not always going to be an extremely painful event (luckily), it usually happens on an evening, when the pupil is about mid dilated. Symptoms can include seeing haloes or rings around lights so if you have experienced this you must tell your optometrist.

Well, I hope that helps you to understand a little bit more about what glaucoma is. It's not just one thing even though we have what I would refer to as normal glaucoma which is sort of everyday glaucoma which we would see the most in practice but there are these other types of glaucoma that we need to look out for and be aware of.