What is 'closed angle glaucoma' and what causes it?

What can be done to avoid this from happening?

thats a good answer by nick...except i want to add the following:

angle closure glaucoma is usually a physiologic and ANATOMICAL/MORPHOLOGICAL problem. in other words the people who get it have a certain specific anatomy inside their eye that they were born with that makes them more susceptible to the condition. some anatomical features that would cause/contribute to angle closure are "narrow angles" and "plateau iris".

and there is at least one preventative measure: laser peripheral iridotomy (LPI)...basically a surgeon takes a laser and burns a hole in the iris to make another "drain hole" and prevent pressure buildup. it works in the vast majority of cases... Source(s): optometrist
http://blog.360.yahoo.com/blog-wsz1uw8ha...

The eye is constantly making a liquid called aqueous which gives it its desired nutrients. As this is constantly being made its also needs to be consantly removed. It moslty drains through the 'angle' which is where the iris (coloured part of eye) meets the cornea (clear part of eye).

If this angle suddenly blocks or become closed the pressure in the eye will build up as it is still making aqueous ...but it has nowhere to go. Think of a sink with a blocked drain....if the drain can't get rid of water as fast as the tap puts it in, it overflows.

Symptoms are a painful, rapidly progressing vision loss. In more severe cases you can get nausea and vomitting. You may also get halos around lights. Basically....if this happens to you go to the hospital emergency ward.

There isn't much you can do to avoid it happening other than having regular eye exams. If the optometrist thinks your angle looks narrow and prone to closing they may refer you to an ophthalmologist to have an assesment and perhaps eye surgery. Hope this helps