 | Glaucoma: What Every Patient Should Know |  |
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As with iridotomy, laser angle treatment is done as an outpatient, one or both eyes can be treated in one sitting, and no pre-operative drugs are needed. You eat and drink normally on the day of treatment. The eye is numbed with drops and an examining lens is put on the eye so you can’t close the eye during blinking. The lens has a mirror to let the doctor see the meshwork all around its 360 degree circle as the lens is gradually turned during treatment. The two types of lasers used are the continuous wave laser (argon or diode type for ALT) or the neodymium:YAG laser tuned specially for this treatment (selective laser trabeculoplasty, SLT). ALT has been used since 1978, while the SLT was developed in the early 2000s. The size of the area illuminated by ALT and SLT are different, but from the patient’s point of view, there is no real difference, since it is unusual for you to feel anything as 80-100 spots are delivered to the meshwork, when the entire 360 degrees are treated. The treatment takes less than 10 minutes per eye.
The eye pressure is measured 45 to 60 minutes after treatment, no patch is used, and glaucoma drops are continued until 6 weeks or more after treatment, which is how long it takes to see the effect (or not). Eye drops containing anti-inflammatory medicine may be used for a few days at about 4 times per day to decrease redness and discomfort, though some doctors do not use these drops. In thousands of laser angle treatments done at our Institute, we have not seen a person whose vision or health was made worse by the treatment itself. That’s a big vote in favor of the small risk of doing laser angle treatment. As described above, when given as initial treatment, nearly 75% avoid taking drops for a period of 3 years (or more). For people already taking eye drops, about two-thirds of those treated have a big enough further lowering of pressure to call it helpful. But, most of those on multiple medications before LTP are still taking some eye drops daily afterward. So, LTP in those eyes is sometimes said to be like “adding another drop.”
The way the ALT or SLT works is thought to be by a micro-injury to the trabecular meshwork. Injured tissue puts out chemicals for healing that apparently signal the cells there to behave more normally, dividing into new cells, and making better surrounding material that lets water out faster. Fluid overlying experimentally treated trabecular meshwork from human eye bank eyes causes untreated meshwork cells to improve their function.
Clearly, we don’t want to cause major injury or to injure all of the meshwork badly, or the pressure would go up instead of down. In fact, in Dr. Quigley's laboratory, he has developed animal models of high eye pressure by extensive lasering of the meshwork. The ALT type treatment affects only 10% of the meshwork directly by its injury, while the SLT pretty much exposes the entire meshwork to energy, but at a lower level. From all present data, the two treatments wind up with the same level of pressure lowering. This means that the level of injury caused by SLT is less per “pound” of meshwork, but it accomplishes the same thing.
Some doctors treat only half of each eye at one sitting of ALT or SLT. The idea is that you can see some lowering from such a treatment and later one could come back and do the other half and get the same effect again. This sounds fine, but the available evidence suggests that treating half the eye gets less effect than treating the whole 360 degrees. If half treatment got a really big effect, it would be a stronger argument for it. Dividing the treatment into halves isn’t wrong, however.
Repeating LTP treatment is sometimes effective if it did some good the first time for a period. When SLT was developed, it was said to be more repeatable than ALT, but prior studies show that ALT is also sometimes effective in a second treatment. But, there has been no study that shows that SLT is more repeatable than ALT. For both ALT and SLT, a small number of patients who had repeated treatments had pressure go higher, even requiring prompt surgical operations.
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