Monday, November 20, 2006

Section 8-A-1: Laser Trabeculoplasty

Laser trabeculoplasty delivers laser energy to the trabecular meshwork. The goal of treatment is to facilitate the outflow of aqueous humor from the eye in order to lower the intraocular pressure (IOP). The exact mechanism of lowering IOP is not completely understood. It is thought that the laser energy causes cellular changes within the drainage angle, which leads to increased aqueous outflow.

Certain patients have better results with laser trabeculoplasty than others. Patient selection is based on the type of glaucoma and trabecular meshwork pigmentation (coloring). There is no correlation between drainage angle pigmentation and the eye or skin color. Angle closure glaucoma is usually NOT treated with laser trabeculoplasty because the angle cannot be visualized for treatment. In addition, those with narrow angles may develop scarring (synechiae) between the cornea and iris with this type of laser treatment. Therefore, laser trabeculoplasty is usually reserved for open angle glaucomas. Patients with primary open angle, pigmentary, or pseudoexfoliation glaucoma tend to do well with laser trabeculoplasty. Some forms of open angle glaucoma, such as glaucoma from trauma or aphakia (previous cataract surgery without intraocular lens replacement), however, may not respond as well as primary open-angle glaucoma. In addition, laser trabeculoplasty is usually avoided in patients with active inflammation, as in uveitic glaucoma, since it can induce further inflammation.
The trabecular meshwork should be examined by gonioscopy (see Chapter 6, Section 6-C). More densely pigmented trabecular meshworks respond better to laser since pigment facilitates the uptake of laser energy (e.g., pigmentary and pseudoexfoliation glaucoma). Lightly pigmented trabecular meshworks may require more laser energy compared to densely pigmented trabecular meshworks, and may be less successful. The optimal candidate is a patient with an open angle with a densely pigmented trabecular meshwork. The eye should be quiet without inflammation. The pre-operative IOP should not be too high since one of the risks of laser trabeculoplasty is a post-operative IOP spike due to transient inflammation. Those with end-stage glaucoma may not be able to tolerate the potential post-laser IOP elevation, and instead may require a filtering surgery (see below).

Argon Laser Trabeculoplasty (ALT)

Argon laser trabeculoplasty (ALT) is a common glaucoma laser surgery, which is performed in an office setting. It uses an Argon laser which delivers energy in blue-green wavelengths (Figure 8-1). A topical glaucoma eye drop (e.g. brimonidine) is given 15 minutes prior to the procedure to prevent a post-laser IOP elevation. The procedure itself usually takes less than 10 minutes. Patients rarely experience discomfort during the procedure. Once the eye is anesthetized with topical eye drop, a contact lens is placed on the surface of the cornea (Figure 8-2). The gonioscopic contact lens allows visualization of the drainage angle. The laser spots are then delivered to the trabecular meshwork. Either 180º or 360º of the angle is treated per treatment session. Each area of the angle is treated only once to avoid scar formation in the angle.

Figure 8-1.
Slit Lamp with Argon Laser used for laser trabeculoplasty.
It may also be used for other ocular procedures including treatment for diabetic retinopathy.

Argon Laser

Trabeculectomy Contact Lens

Figure 8-2. Contact Lens used in Laser Trabeculoplasty.

After the laser procedure, another glaucoma eye drop is administered to prevent post-operative IOP spike. The IOP is measured 1 hour after the procedure to ensure that it is stable. Patients are advised to continue the glaucoma medications that they were using prior to the laser treatment. In addition, a short course of topical steroids is given to reduce post-operative inflammation. Patients return for follow-up examination in 4-6 weeks to determine if the ALT treatment decreased the IOP. If IOP is still uncontrolled, additional surgical intervention may be necessary.

Success rates of the ALT vary. Overall success rate is approximately 50% over 5 years. After this time, many patients require additional intervention to control their IOP.

Complications of ALT

The most common complication after ALT is the post-laser IOP spike. Fortunately, the pressure elevation is often transient and typically causes no long-term complication. This occurs from the inflammation that ensues after laser energy is delivered to the trabecular meshwork. It is treated with additional glaucoma medications as needed. Anterior segment inflammation (iritis) is another complication that may occur. Post-laser topical steroids are given to control inflammation. Topical steroids are used for several days to a week after treatment. Scarring between the iris and the angle (peripheral anterior synechiae) may develop after the laser, as well as changes to the peripheral cornea. These complications are uncommon in eyes with open angles, but may be more likely in narrow angles.

Selective Laser Trabeculoplasty (SLT)

A more recently developed glaucoma laser procedure is selective laser trabeculoplasty (SLT). This procedure utilizes a neodynium:YAG laser. Unlike ALT, SLT allows the surgeon to repeat the laser surgery over the same area of the angle, because the laser targets only the pigmented cells in the trabecular meshwork while sparing the non-pigmented cells from a thermal damage. Otherwise, the procedure is very similar to ALT. Either 180º or 360º of the angle is treated. It is performed in an office setting with administration of a glaucoma drop before and after the procedure, very similar to the ALT.

Potential complications of SLT are similar to ALT. There is the possibility of post-laser IOP elevation, which is minimized by the administration of glaucoma drops at the time of the laser treatment. An IOP check is performed 1 hour after the procedure. Patients are again advised to continue their previous glaucoma medications and are given a short course of topical steroids.


Anonymous Seth said...

Okay not to sound stupid or anything but, what on earth is Trabeculoplasty? I am not sure what that is. I would like to know though I am all for learning something new. I just happened upon this blog but, would love to learn more about what you're talking about. Thanks for any info you can give me on this.


11:16 PM  

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