The “angle” in the eye is the area where fluid drains out of the eye; it is also called the “drainage angle”. Fluid is constantly produced inside the eye. This fluid must be constantly drained or the eye pressure will rise. This may occur if the drainage angle closes. High eye pressure can damage the optic nerve, causing permanent loss of vision. If the eye pressure goes up rapidly and reaches a very high level, pain, blurred vision, halos, redness, and even nausea and vomiting can result. (Aside: the drainage of tears occurs outside of the eye and is not directly related to this internal drainage system of the eye.)
To understand angle closure, it’s essential to picture the angle structures. The back wall of the angle is made up of the iris. The iris is the blue, green, or brown-colored ring inside the eye that outlines the pupil. The front wall of the angle is made up of the clear cap on the front of the eye, called the cornea. These two structures meet at the drainage angle, which goes all the way around the eye. Looking directly at someone, the angle occupies a circle surrounding the iris.
In most eyes, the drainage angle is wide open. The more common forms of glaucoma in Western countries do not involve angle closure. Instead, there is microscopic blockage or damage inside the tissues of the drainage angle which cannot be seen by examining the eye. These are called “open angle glaucomas” to contrast them with angle closure.
The most common form of angle closure is called primary angle closure, and is discussed below. However, there are many other conditions that lead to angle closure. Conditions that cause scarring in the drainage angle, due to formation of membranes or abnormal blood vessels, may lead to angle closure, and often require surgery. As we get older, the natural lens inside the eye grows and can push the iris more forward, making the angle more narrow. The tissue behind the iris, called the ciliary body, can push the iris forward, making the angle narrow. Swelling or bleeding in the back of the eye and abnormal flow of fluid through the eye can also push the iris forward. After eye surgeries, more rare, complex forms of angle closure may also develop; these situations often require a careful evaluation and treatment by a specialist. These and other factors may all contribute to angle closure to a varying extent, and are often lumped together as “secondary angle closure”.
The principal problem in most primary angle closure is called pupillary block. This occurs when fluid is trapped behind the iris, pushing it forward. In severe cases this can close off the drainage angle. It’s hard to tell if pupillary block is present, and it probably contributes to at least 2 out of 3 cases of angle closure. Often times the first step in treating angle closure is to treat any pupillary block. If an eye is even felt to be at high risk for angle closure, pupillary block may also be treated to reduce the risk of this problem occurring.
Pupillary block is treated by making a small hole in the iris with a laser, called an iridotomy. This allows any fluid trapped behind the iris to flow freely into the front of the eye, relieving any pent-up pressure behind the iris. The iris, which was billowing forward like a sail in the wind, may then fall back and open the drainage angle, usually immediately.
The laser vaporizes the iris and causes inflammation, which can cause (usually temporary) discomfort and/or rise in the eye pressure. Occasionally a line of light may be noticeable by the patient from the light entering the opening, but it’s less common with current techniques. Retina problems are rare.
There is a vocal minority of patients who have posted serious complaints about problems they have had after the laser on the internet. In reality, serious or lasting complications are rare, and laser iridotomy is a very common procedure. Since the procedure is not risk-free, however, not everyone at risk for angle closure may get the laser. It is controversial who should have a laser iridotomy, since only a minority of patients with narrow angles develop angle closure, and other than patients who already have signs of angle closure, we can’t predict who will have a problem.
Even when pupil block is relieved, other factors, mentioned above, may keep the angle narrow. Unless significant scarring has set in, another type of laser treatment called iridoplasty can be used to open the angle. Iridoplasty involves heat-shrinking the iris where it meets the angle in order to widen the angle. Removal of a cataract may also be very effective in opening the drainage angle. Once the angle is sufficiently scarred, a new drain may have to be surgically created to lower the eye pressure. Thus, angle closure is best prevented or treated early.