This technique is used in patients who have ‘relative pupillary block (RPB)’ that is leading to angle closure glaucoma. By placing a very small hole in the peripheral iris, the pressure is equalized between the front and back of the iris so that it no longer is pushing itself forward to close the trabecular meshwork. The normal flow of aqueous humour starts behind the iris in the ciliary body, then through the pupil into the anterior chamber of the eye, in front of the iris. Patients with RPB have a relative blockage in how fast the aqueous can flow past the pupil so that the iris ends up bowing itself forward to close off the peripheral iris against the trabecular meshwork, thus leading to the pressure shooting up much higher in the eye. By putting a small hole in the iris, the fluid has another means of getting from behind the iris to in front of the iris so that the iris is less likley to push itself forward, close off the angle, and raise the eye pressure.
Some patients with Pigmentary Glaucoma may also be candidates for a Laser Peripheral Iridotomy. Part of the mechanism of the raised pressure in these patients is a ‘reverse pupillary block,’ such that the pressure in front of the iris is greater than the pressure behind the iris. When this occurs, the back of the iris rubs itself on the ‘zonules’ that hold the lens of the eye in place, causing pigment to get dispersed within the front part of the eye. The body’s immune system can react to the presence of this extra pigment in the drainage channels of the trabecular meshwork by partially damaging the meshwork in its attempt to rid the eye of the extra pigment. In patients who have this reverse pupillary block, once again the iridotomy equalizes the pressure between the anterior chamber (in front of the iris) and the posterior chamber (behind the iris.) With this pressure gradient eliminated, the iris should no longer rub itself against the zonules and release pigment.
The Nd:YAG frequency-doubled laser at 532nm is used to perform this procedure. If a patient’s iris is very thick and darkly pigmented, sometimes Dr. Schertzer will opt to first use the Argon laser to thin out a small area of the iris before continuing with the Nd:YAG laser to complete the iridotomy. The argon laser has a greater tendency to increase inflammation which could result in the iridotomy closing off therefore it’s use is generally kept to a minimum.
Laser Peripheral Iridotomy is an in-office technique at the West Coast Glaucoma Centre. After instilling a drop of topical anaesthetic, a lens is touched to your eye in order to bend the laser light and focus it on the peripheral iris, searching for the thinnest area. The technique takes approximately five minutes per eye. Afterwards, a glaucoma eye drop will also be instilled to reduce the chance of a sudden spike in eye pressure and you will wait in the waiting room for 30-60 minutes so that we can recheck you before you leave. Follow-up will be arranged for 1 week later and 6 weeks later and you will likely take an anti-inflammatory eye drop for several days to make sure you do not have any discomfort.