The procedure is done as an outpatient and it is best to have someone along to take you home, as your vision in one or both eyes might be poor for driving or walking for about a day, though it isn’t usually badly blurred. We can treat one or both eyes at one sitting. There is no preparatory medicine needed on the day before or morning of, and you should take any usual eyedrops that were prescribed for daily use. After the preliminary exam, an eye drop of pilocarpine (see section Glaucoma eye drops: choices, choices) is put into the eye to make the pupil small and the iris thinner. This takes 15-30 minutes. You will get a pressure sensation, often felt in the eyebrow, and your vision can change temporarily. The eye is numbed with anesthetic eye drop or ointment and a lens is put on the eye, held by the doctor’s fingers to keep your eyelids out of the way and to magnify the view. You will be sitting up at the instrument called the slit lamp with a chin rest and bright light shining from binoculars that the doctor looks through. You help by keeping the other eye open and staring straight ahead between blinks. It’s OK to blink, since the eye getting treated can’t close with the examining lens in place. There will be a gooey jelly that is used to keep the lens on your eye and the doctor will clean it off when the procedure is done.

The most commonly used laser is the neodymium:YAG type, which treats the eye so fast that you won’t have a chance to move your eye during laser applications. When the laser fires, you get a sensation that something happened. It's typically not unpleasant, just a little startling if the doctor doesn’t warn you first. We often need to make several deliveries of laser to produce a hole about one half a millimeter in size, about the size of a ball point pen tip (Figure 18). That’s all it takes to let aqueous flow from behind to in front of the iris and fix the problem. It’s pretty uncommon that you or someone else will see where the hole was made, though if you look closely, you’ll later possibly see a black dot where it is. Because the laser is focused down to a point at the iris inside the eye, it doesn’t have concentrated power anywhere in the eye except there, so it doesn’t damage the wall of the eye or anything behind the iris. You won't have a hole in the outer wall of the eye.

Among glaucoma specialists there is a controversy about where on the iris the best place for the hole is. It doesn’t matter from the point of view of water moving through, since anywhere works. A small number of persons after iridotomy report that they see an additional line of light around streetlights, or, they see more glare in general. Some believe that this is because the hole in the iris is right behind where the upper eyelid and its tear film lies, producing an optical effect called light scattering. For this reason, some put the hole far up in the peripheral iris, while other doctors put it right out in the middle of the iris (at 3 or 9 o’clock if the iris were a clock). In one large study, very few people had this problem, whichever position for the hole was randomly chosen. Most persons find this disturbing optical effect goes away with time.

For the first hour after treatment, vision is blurred, but it clears quickly. One hour after treatment the pressure is checked, since occasionally it rises substantially and needs treatment for a while with drops to make it safe again. No eye patch is used. Often, anti-inflammatory eye drops are given 4 times per day for a few days. The next visit is 1 - 6 weeks later. If the laser hole is not open at 6 weeks after the initial treatment, it is retreated, which is typically pretty quick and easy. Making a hole is harder in thicker, brown irises, such as in African- or Asian-derived persons. In them, we sometimes have to do up two treatments with two separate types of lasers in sequence, the first being a continuous wave laser (diode) to thin down the iris, followed by the neodymium:YAG to punch through. About one in ten times in this kind of patient it can take two sessions to make a full hole of the right size.

Once a laser iris hole is made, it’s pretty much open for good. The iris doesn’t heal as do other body tissues, probably because the aqueous fluid that surrounds it contains chemicals that prevent healing under normal circumstances. The exceptions to the no-healing rule are eyes that have new blood vessels growing in them or eyes with inflammatory processes (neovascular and inflammatory glaucoma, see section Secondary glaucoma). Because the normal situation of no-healing is changed by these processes, laser iris holes in those eyes can close up and are watched more closely.

There is some limited evidence that making a hole in the iris speeds the development of cataract, perhaps because the movement of aqueous is re-routed through the hole and doesn’t uniformly bathe the lens as it normally does. A large study in which the Glaucoma Center of Excellence participated failed to find any speeding up of cataract in hundreds of treated eyes. Of course, if the eye develops an acute angle closure crisis because the hole wasn’t made, a cataract is pretty much guaranteed to develop soon.