Overview of Laser Trabeculoplasty
Glaucoma is a condition that affects the eye, causing damage to the optic nerve, which can eventually lead to blindness if not treated. There are several risk factors for developing glaucoma, but the only one we can control is the pressure inside the eye, also known as intraocular pressure (IOP).
There are different ways to treat glaucoma, such as medication or surgery, but another method called laser treatment has become more popular recently. There are two main types of laser treatments used to help drain fluid from the eye and reduce pressure: argon laser trabeculoplasty (ALT) and selective laser trabeculoplasty (SLT).
In 1979, Wise and Witter first introduced ALT as a treatment for a type of glaucoma called open-angle glaucoma (OAG). They showed that ALT was safe and worked well in lowering eye pressure. In a long-term study, eyes treated with ALT were compared to eyes treated with medication alone over a period of 2.5 to 5.5 years. The results showed that ALT was just as effective in reducing eye pressure. However, as the effect of ALT tends to wear off over time, it’s often used alongside other treatments rather than on its own.
The other laser treatment, SLT, has become more popular recently. SLT uses a different type of laser and works in a similar way to ALT, but is less damaging to the eye. Research has shown that both ALT and SLT are equally good at reducing eye pressure in people with OAG.
Anatomy and Physiology of Laser Trabeculoplasty
The angle of the anterior chamber is part of the eye. It is where the cornea and iris meet. Doctors can view this angle by using a special type of examination called gonioscopy. The angle is made up of several parts, moving from the back to the front.
First, there is the Ciliary Body Band. This is the forefront of the ciliary body, which is part of the eye that produces a fluid called aqueous humor. It appears as a grey or brown band when seen through gonioscopy, and it’s the furthest structure at the back.
Next, we have the Scleral Spur. This is a band that connects with the ciliary body at the back and the corneoscleral meshwork at the front. It’s usually seen as a white band during gonioscopy.
Then we find the Trabecular Meshwork. This is a structure located in front of the scleral spur. It appears as a band and has two parts—a part that doesn’t have color and a part that is pigmented. The colored part is responsible for draining the fluid in the eye, which explains its coloration.
The Trabecular Meshwork is in charge of regulating the outflow of about 90% of the aqueous humor, which is the clear fluid inside the eye. There are three parts in it: the uveal meshwork, the corneoscleral meshwork, and the juxtacanalicular meshwork. These parts have different sizes and offer a different level of resistance to the fluid’s movement.
Lastly, there is the fine ridge called Schwalbe Line, situated in front of the Trabecular Meshwork. It’s essentially the prominent end of the cornea’s Descemet membrane and represents the boundary of all the structures that make up the angle of the anterior chamber.
The fluid in the eye, the aqueous humor, travels from the back to the front. It leaves the anterior chamber primarily through the Trabecular Meshwork and first descends via the pupil. About 90% of the fluid passes through this route. Another 10% uses the uveoscleral pathway, and some fluid also drains through the iris.
Why do People Need Laser Trabeculoplasty
A laser trabeculoplasty is a type of treatment usually done when a person has open-angle glaucoma (OAG), a condition that can damage your optic nerve and lead to vision loss. This procedure becomes necessary in certain situations:
1. When a patient with OAG is not having their intraocular pressure (IOP) – that is the pressure in their eyes – controlled by the medicines they are taking. This might be the case even when they’re using the maximum amount of medicine that they can safely tolerate. IOP is important because high levels can damage the optic nerve, which can lead to vision loss.
2. For patients with OAG who are not able to regularly take their medicines as prescribed, and their IO remains above the target level, causing their optic nerve to continue to get worse.
3. For patients with OAG who are not able to tolerate the side effects of the medicines they are given.
4. For patients with special types of glaucoma known as pseudoexfoliation or pigmentary glaucoma. Pseudoexfoliation glaucoma occurs when extra material is produced in your eye and clogs the drainage system, causing pressure to build, while pigmentary glaucoma is when pigment granules from your iris build up in the drainage channels, slowing or blocking the outflow of fluid from your eye.
5. For patients with angle-closure glaucoma who have had a successful iridotomy (a small hole made in the iris to help fluid flow within the eye). Angle-closure glaucoma is a rare type of glaucoma that happens when the drainage system in your eye becomes completely blocked, causing your eye pressure to suddenly rise.
6. When a person is scheduled to have glaucoma surgery, but it needs to be postponed or delayed for some reason.
When a Person Should Avoid Laser Trabeculoplasty
There are certain circumstances when laser trabeculoplasty, a procedure to treat glaucoma, cannot be performed:
- Inflammatory glaucoma: This type of glaucoma causes inflammation and following a laser treatment, this inflammation can worsen, causing further increases in intraocular pressure (IOP – the fluid pressure inside the eye).
- Advanced glaucoma: Usually, if the glaucoma case is too far advanced, laser treatments may not be effective.
- Poor visualization of the trabecular meshwork (TM): The trabecular meshwork is the part of the eye that the laser treatment targets. If the doctor can’t clearly see it due to adhesions (synechiae) in the eye, the procedure might not be successful.
Equipment used for Laser Trabeculoplasty
For our laser systems, we use two types of lasers. The Argon green laser light is used in a procedure called ALT, while the Q-switched Nd: YAG laser is used in another procedure called SLT.
We also use special lenses that help us visualize the front part of your eye, which we call the anterior chamber. In laser trabeculoplasty, we use a contact lens that has a mirror and an anti-reflective coating on the front surface.
We have a range of lenses that we use, depending on the specific needs of your eye. For instance, the Goldmann type 3-mirror lens has one mirror at a 59° angle. On the other hand, the Thorpe 4-mirror gonioscopy lens has all its mirrors tilted at 62°. This lens helps us view all areas of the anterior chamber at the same time.
The Ritch trabeculoplasty lens has 2 mirrors at a 59° angle and 2 mirrors at a 64° angle. This lens helps us view different parts of your eye – the inferior quadrants and the superior angles. It also has a certain type of lens, called a 17 diopter planoconvex lens, that enlarges images, making them seem 1.4 times bigger. This reduces the size of the laser spot we use in the treatment.
Finally, we have the Latina lens, specifically designed for SLT procedures. It has a single mirror at a 63° angle and makes images appear at their original size.
Who is needed to perform Laser Trabeculoplasty?
The group of people who carry out a procedure called laser trabeculoplasty are made up of different professionals. These include the main doctors performing the procedure, often a doctor who has finished their training (attending surgeon) and a doctor who is still in training (resident surgeon). There are also nurses who help with medical care and operative room technicians who assist with preparing and maintaining the surgical equipment. They all have different roles but work together to ensure the procedure is done correctly and safely.
Preparing for Laser Trabeculoplasty
When preparing for a surgical procedure that helps treat glaucoma (an eye condition that can lead to vision loss) known as trabeculoplasty, which involves treating the part of the eye called the trabecular meshwork, you will undergo a detailed health exam. This is important to ensure you’re a good fit for the procedure and will likely include the following steps:
1. Details about your overall health and any specific issues you’ve had with your eyes will be taken into account.
2. There will also be various physical examinations focusing on your eyes to be completed:
– An examination of the angle of the front part of your eye, called the ‘anterior chamber’, using a special tool known as a gonioscope. Here, your doctor will look for the visibility of the trabecular meshwork (a tiny part of your eye that helps control eye pressure) because it is the targeted part for surgery. If your trabecular meshwork is visible when asked to look towards the mirror, it means that there’s enough space in the angle for the treatment. The doctor will also check for eye conditions like ‘synechiae’ that can block access to the trabecular meshwork and hence hinder the procedure.
– Measurement of the pressure inside your eye to establish a ‘baseline’ value that can be compared with the pressure after the procedure.
– Checking the thickness of your cornea (the clear front surface of your eye).
– Using a device called a slit lamp, the doctor will check your optic nerve for any signs of glaucoma damage.
– Mapping out your field of vision.
3. You would likely be given medication to help lower eye pressure. This is given to reduce the risk of a sudden rise in eye pressure after the surgery. A topical anesthetic, applied directly to the eye, might also be used to numb your eye just before the procedure.
Before the procedure happens, the doctor will explain to you all the risks, benefits, and alternatives to the procedure, and you will be asked to sign a consent form. It’s important to understand that although the surgeon will do their best, the procedure may not always work as planned.
How is Laser Trabeculoplasty performed
The following text describes how lasers are used to lower eye pressure, a common risk factor for glaucoma. There are several popular theories on how this process works:
1. Cell activity – This theory suggests that lasers stimulate cellular movement in the eye. With the help of immune cells, structural changes occur within the eye that increase the amount of fluid that can flow out of the eye, reducing eye pressure.
2. Protein production – After laser treatment has been given, the eye tends to detect higher levels of specific proteins. These proteins help reorganize the eye’s structures and increase the rate of fluid outflow, decreasing eye pressure.
3. Canal conductivity – Lasers can increase the fluid-carrying capacity of the eye’s drainage channels, leading to more fluid flow and lowered eye pressure.
Different types of lasers produce different results on the eye’s internal structures. For example, the Argon Laser induces tissue damage, while the Selective Laser disrupts the cells responsible for fluid drainage in the eye.
In both methods, lasers are focused on specific targets to optimize their effects. The Argon Laser is shorter in duration, but higher in intensity and is applied to the boundary of the front and back of the eye. The Selective Laser has larger, less intense, and rapid bursts and is applied specifically to the eye’s fluid drainage structures.
Both techniques may induce tiny bubbles or blanching (whitening) in the targeted area, which signals a successful application. Usually, the whole eye isn’t treated at once due to the risk of pressure spikes. Instead, treatment is often split into different sessions. Nevertheless, on occasions, the entire eye can be treated in a single session with the Selective Laser.
Possible Complications of Laser Trabeculoplasty
When having a type of eye treatment known as laser trabeculoplasty, there are a few possible complications to be aware of:
1. An increase in Intraocular Pressure (IOP) – IOP is the fluid pressure inside the eye, and it’s the most common complication people have after this treatment. This can be reduced by taking certain eye drops (alpha-adrenergic agonists) 30-60 minutes before the laser procedure. However, the chance of an IOP increase can be higher if:
– Higher energy levels are used during the procedure,
– The laser treats a full circle (360°) around the eye
– The laser is placed closer to the back of the eye,
– There’s a lot of pigment (color) in the part of the eye being treated, or
– Your eye naturally has a lower amount of fluid flow.
These increases in IOP are usually temporary, happening in the first hour and relieving with medications, but if it stays high, surgery may be needed.
2. Mild inflammation of the iris (the colored part of your eye) – This is known as low-grade iritis.
3. Development of something called Periocular Adhesion Syndrome (PAS) – This is where parts of your eye that should be separate start to stick together.
In addition, corneal edema (swelling in the clear front surface of your eye) can occur due to a reactivation of the Herpes Simplex Virus (HSV). This happens because the inflammation caused by the laser can wake up the dormant virus. This condition is also known as hyphema.
What Else Should I Know About Laser Trabeculoplasty?
The effectiveness of both types of laser eye surgeries to treat glaucoma – Selective Laser Trabeculoplasty (SLT) and Argon Laser Trabeculoplasty (ALT) – tends to lessen over a prolonged period. A study that compared the two types of laser surgeries found no substantial difference in their ability to lower Intraocular Pressure (IOP), which is the pressure inside your eye. Both types of surgeries can decrease the daily fluctuation of IOP.
In different groups of patients with Open-Angle Glaucoma (OAG, a common form of glaucoma), both kinds of surgeries have been effectively used as compared to non-surgical treatment. In a specific type of glaucoma called pseudoexfoliation glaucoma, SLT has been found just as effective in patients with artificial lens implants, compared to those with natural lenses, whereas ALT is mainly done in people with their natural lenses.
Laser surgeries are a cost-effective treatment and can be used in combination with other therapies or control IOP when surgical treatment is postponed. It is becoming an increasingly popular first line of treatment in several patients with OAG.
