aqueous fluid flow, shown in blue (blue)
The eye is partly filled with a watery fluid, called 'aqueous'. The aqueous is made in the middle chamber of the eye. The aqueous flows forward into the front chamber, and leaves the eye in a the eye's drainage system.
From the drainage system, it flows into the blood stream. (This has nothing to do with tears; tears cover the front surface of the eye only.)
The diagram opposite shows how aqueous flows. The middle chamber is known as the 'posterior' chamber, and the front chamber the 'anterior' chamber. Aqueous flows from the posterior to the anterior chamber, then out of the eye
Anatomy of the eye. Close up on right, fluid flow as below.
The eye is partly filled with a watery
fluid, called 'aqueous'. The aqueous is made in the middle chamber of the eye, secreted
by the ciliary body. The aqueous fluid normally flows forward into the front
chamber, and leaves the eye in a the eye's drainage system (the trabecular meshwork and hen the canal of schlemm).
From the drain (canal of schlemm), the aqueous flows into the blood stream. (This has nothing to do with tears; tears cover the front surface of the eye only.) In open angle glaucoma the blockage is in the trabecular meshwork.
In narrow angle glaucoma the iris moves forward and blocks the 'angle'.
If the drain of the eye blocks or is blocked, the fluid cannot drain out of the eye.
the fluid cannot drain out, the pressure in the eye goes
up. This is like a tyre being pumped up and going a little 'hard'.
The extra pressure then presses on the nerve at the back of the eye.
The optic nerve is the 'electric wire' of the eye that takes messages about what you see to the brain. See animation.
As aqueous fluid cannot drain out of the eye, flow is directed back and pressure rises
The pressure presses on the optic nerve at the back of the eye, and as the nerve is damaged the sight becomes reduced. As nerve becomes damaged, examination may show the damage as 'caved in'. Medically we call it 'cupped'.
If you have chronic angle closure glaucoma the front/anterior chamber is usually smaller than normally. (A simplified explanation!)
normal eye & fluid flow
small eye...small eyes are more prone to narrow angle/acute glaucoma
is 'made' in the ciliary body (blue blob), but cannot flow past
the iris or out of the eye the normal way. Pressure is transmitted
to the optic nerve which it damages.
The aqueous pushes the iris forward (see below) and animation .
Because the anterior chamber of the eye is smaller than usual, the process may begin with a blockage between iris and lens (opposite: norally there is a gap between the iris and less as above). As a result there is
not enough space for the aqueous fluid to flow to the front chamber
of the eye and out of the eye.
Then... the fluid pushes the iris even further forward, trapping more fluid in the eye (blocking the entrance to the drainage system). As the aqueous fluid cannot drain out of the eye, this puts the pressure up and damages the optic nerve. This is explained better in this animation.
Primary angle closure is defined as an angle hat is 75% closed or pas.
Acute vs more gradual angle closure glaucoma
This blockage can develop all of a
sudden, perhaps one day coming out of the dark into a well lit
room, as the pupil reaches a 'mid-dilated' size. This causes
The blockage may be more gradual, 'chronic narrow angle glaucoma', this page.
Alternatively, you may have open angle
glaucoma (see) and then this extra
blockage may develop...'open angle glaucoma with narrow angles'. There are many different terms used
to describe these conditions.
Ethnicity and acute glaucoma
Similarly some Asian patients (Taiwanese for example) or Inuits, are far more prone to acute of chronic narrow angle glaucoma at a younger age. In such communities screening services need to examine patients to identify patients who need laser iridotomies.
as the iris gets pushed forward, a secondary blockage develops here (black arrows) at the entry point to the trabecular meshwork and the canal of schlemm (the drainage system).
The iris...when it is pushed forward in this way blocks the entrance to the drain, so pressure goes up.
The condition may develop gradually ('chronic'), as with most glaucoma, and there are no symptoms. The condition may be identified by optometry tests or other eye examinations. (Chronic narrow angle glaucoma). Later, there may be headaches or loss of sight, but by then some vision is lost.
In some people mild attacks of acute glaucoma may be occurring. There may be episdoes of blurred hazy sight and slight eye pain or headache.
The hole made with laser
Laser was the main treatment for this condition at the beginning. How to laser PIs for professionals. It is no longer recommmended in patients over 50y, with cataracts, high pressure, or dark thick irisis (Cataract surgery preferred if treatment is needed.)
An hour before laser you need drops to make your pupil small. These may give you a headache. Tablets keep the eye pressure down for the first day, and these can make you feel a little funny, with pins and needles.
The laser 'Laser' is a type of very bright focused light. You sit at the laser machine, then drops are used to anaesthetise the front of your eye, and a small contact lens is placed on your eye. When the button is pressed you may feel a slight pain lasting a second or less.
The laser hole The laser makes a tiny hole in the iris of your eye. The hole is invisible to the naked eye. Once the hole is made fluid can flow though to the front chamber and then out of the eye. This hole keeps the eye pressure down. Week of laser You need anti-inflammatory drops for 2 weeks (such as dexamethasone), as well as your regular glaucoma drops if you have any.
Month after laser Many people do not need drops after 4 weeks. Occasionally the laser only goes half way through the iris, and you may need the hole completed a week or two later. See animation
Laser completely prevents an 'attack' of acute glaucoma, so this will never be a problem. However, some people with chronic angle closure glaucoma may still have a slightly high pressure even after laser, and they need drops indefinitely. Imagine an overflowing sink. If you remove the plug (with laser), there may still be a blocked drain. The diagram opposite shows where the remaining blockage may remain (the black rectangle).
Technically the blockage is in the trabecular meshwork, which is the drainage system of the eye. The blue arrow is the site of the laser hole. If you need drops you will be followed up in the outpatient clinic. If your doctor thinks you are lucky enough not to need drops, always have your eyes checked by your optometrist every year as a precaution. See animation.
About one third of patients will not need drops after laser. One third will need drops. Of the other third, some may need drops later. Some of the patients needing drops may need treatment for plateau iris, which includes laser iridoplasty or cataract surgery (our page)
aqueous flow in a younger patient
Thickening of the lens of the eye (cataract) contributes to the angle closure. This happens naturally as we get older, but may happen earlier if we develop a cataract. As cataracts are common as we get older, (and more common in smokers), we are more prone to acute glaucoma as we get older. Some patients with unusually small eyes may develop acute angle closure glaucoma at a younger age.
Reduced pressure if angles narrow JCRS 14
aqueous flow in a older patient (rarely patients can be younger...they will have small eyes)
aqueous flow is restored after cataract surgery
Ethnicity and acute glaucoma
Similarly some Asian patients (Taiwanese for example) or Inuits, have narrower anterior chambers and crowded angles and are far more prone to acute glaucoma at a younger age. In such communities screening services need to examine patients, to pick out patients who need laser iridotomies. BJO 19
See this page .