Some people have eye(s) where the front structures are or become crowded. This is commonly associated with marked long sightedness or the development of cataract, but might just be a consequence of aging.
This can lead to an obstruction to the flow of fluid through the normal drainage channels out of the eye and back to the blood vessels. When such a situation occurs the patient may have a sudden, severe onset of very high pressure ( acute angle closure glaucoma) in the eye associated with pain and blurring of vision or the presence of halos seen around lights. This particularly occurs at night when the pupil is larger than during the daytime. An attack can cause permanent damage to the vision.
Other times the pressure elevates very slowly and painlessly and is caused by a slow closure of the angle so called "chronic angle closure glaucoma" If the doctor finds that there is a significant risk of this occurring, or if you have had past symptoms as described above, then the common treatment is to use a laser to make a hole through the substance of the iris to allow the fluid to escape easily to the drainage area in the eye. Once the laser valve is made it is usually permanent.
This laser has a very low risk of side effects. There may be a temporary rise in pressure associated with it, there may also be minor bleeding and/or blurriness of vision for a short time following the treatment.
Sometimes, as well as using the laser treatment, drops are required to maintain the eye at a satisfactorily low pressure.