Expert

Peripheral Iridotomy: A Laser Procedure for Narrow Angles

Sunday, June 1, 2014
A diagram of the eye showing the process of peripheral iridotomy.

In angle-closure glaucoma or in patients at risk for this condition, laser iridotomy is the preferred method of treatment.

In treating glaucoma with lasers, it is important to understand what type of glaucoma you may have. For example, one type of laser surgery (laser trabeculoplasty) is often used in open-angle glaucoma when medications are unlikely to work, do not work, or produce intolerable side effects. In some patients, laser trabeculoplasty may be the first mode of therapy if eye drops are not practical or likely to be used improperly.

On the other hand, in angle-closure glaucoma or in patients at risk for this condition, another type of laser surgery (laser iridotomy) is the preferred method of treatment right from the beginning. The “angle” that is being referred to is the angle between the iris, which makes up the colored pupil part of your eye, and the cornea, which is the clear window front part of your eye. The video below provides a very good representation of the eye's "angle."

Angle-Closure Glaucoma Video

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Diagnosis

When the angle is open, your ophthalmologist can see most, if not all, of your drainage system when he or she uses a special mirrored lens to examine it; this procedure is called gonioscopy. When the angle is narrow, your ophthalmologist can only see portions of the drainage angle, and in acute angle-closure glaucoma, none of the drainage angle is visible. Using this mirrored lens, or gonioscopy, is the most common way your ophthalmologist will detect that you have narrow angles, and you may be diagnosed as a primary angle-closure “suspect.”

What Causes Narrow Angles?

You may have narrow angles because of certain anatomical conditions, such as having a shorter eye than the average person, being hyperopic (far-sighted), or having a growing cataract that gradually narrows the angle over time. You may also have a closed angle because of inflammatory conditions, such as uveitis, or vascular conditions, such as diabetes, that gradually cause what is termed “secondary angle closure” over time.  

Acute Angle-Closure Glaucoma: A Medical Emergency

If you are a primary angle-closure “suspect,” you may be at risk for a potentially very serious condition called acute angle-closure glaucoma. In this situation, the pressure may slowly build up in the back part of the eye due to the narrowness of the angle. This pressure build up gradually increases and causes the iris to push forward and the angle to narrow even further, eventually blocking off most or all drainage of fluid from the eye. When this happens, the eye pressure increases dramatically. The cornea may become cloudy due to the increased pressure, the eye may become quite red, and vision will be decreased. The increased eye pressure can also cause pain, sometimes so severe that it leads to nausea and vomiting. The treatment is to lower eye pressure using eye drops and potentially oral medications, but the definitive treatment is to perform a laser iridotomy. 

In this procedure, a tiny, microscopic hole is placed in the iris under the upper eyelid at the 12-o’clock position (or at 3- or 9-o’clock positions depending on surgeon preference) to allow the iris to fall away from the drainage area inside the eye. You can think of it as an escape valve, so that the pressure in the front of the eye equalizes the pressure in the back of the eye.

Angle-Closure "Suspects"

Laser peripheral iridotomy is the same procedure used to preventively treat primary angle-closure suspects, or patients with narrow angles that are at risk for an angle-closure attack. Although there are some criteria that ophthalmologists use to determine whether a patient with narrow angles is at high enough risk to warrant this preventive procedure, there is no way to predict whether any given individual will actually go on to have an angle-closure attack if left untreated.

Risks and Benefits of Laser Peripheral Iridotomy

It is understandably difficult for patients who see an eye care provider during a routine visit to be told that they have narrow angles requiring a laser surgery. Therefore, it is important to understand the risks and benefits of laser peripheral iridotomy in order to make an informed decision about whether to undergo the procedure. As outlined above, the benefit of this procedure is that it may prevent you from having a potentially visually devastating angle-closure attack. Although the risk of progressing to an angle-closure attack is unknown, the possible outcome is so impactful that it is worth considering the benefit of laser peripheral iridotomy.

In terms of risks, common complications include a little bleeding from the iris (almost always transient). If you are taking a blood thinner such as aspirin, Plavix (clopidigrel) or Coumadin (warfarin), make sure you tell the doctor. Depending on your ophthalmologist’s preference, it may be advisable to discontinue the blood thinner a week or so before the surgery. If bleeding does occur, some pressure may be placed on your eye with a contact lens and your vision may be a little blurry for a few hours to a day. Mild light sensitivity and a scratchy feeling on the surface of the eye are also common for 24-72 hours after the procedure. Very rarely, the patient may experience an extra “ghost image” through the tiny opening in the iris. This may be annoying for a while but almost all of the few patients who develop this complication eventually get used to it. Lastly, it is not uncommon to have a mild eye pressure elevation after the hole through the iris is made since iris pigment is released during the procedure. Therefore, your eye pressure will be checked 30-60 minutes after the iridotomy, and in cases of mild eye pressure elevation some eye drops may be used to lower the pressure.

Alternatives to Iridotomy

Alternatives to laser iridotomy include a surgical iridectomy in which an incision is made in the eye to remove a portion of the iris. Surgical iridectomy has more significant risks than laser iridotomy and is rarely used anymore. The other alternative is to do nothing, which runs the risk of an acute attack of angle-closure glaucoma that may be difficult to control and cause serious visual damage.

Prevention

Although not all patients with narrow angles go on to develop angle-closure glaucoma, laser iridotomy is often performed as a preventive measure because of its relatively low risk compared to potential serious consequences of angle-closure glaucoma. If an iridotomy is performed early enough in the process, it may be curative. Some patients still require drops or supplemental laser treatment, however. Practically speaking, laser surgery has the advantage of being an in-office procedure with a very low risk for serious complications.

What Happens During an Iridotomy?

In most laser surgery, the eye is anesthetized with the same eye drops used for measuring the eye pressure. Some additional preparatory eye drops may also be used. After the patient is set up in front of the laser, which looks like the typical examination microscope, a large contact lens is temporarily placed on the eye. The laser beam is aimed and multiple laser “shots” are placed into the iris. Laser surgery is not painful although the patient may feel a “pop” in the eye or an occasional pinprick type sensation. After the procedure is over, the contact lens will be removed and the eye rinsed out. Another eye drop may then be given.

After the laser treatment, you may notice some blurry vision, mild discomfort, or a foreign body sensation in your eye. These symptoms are usually transient and are gone within a few hours to a few days. Your eye pressure will be checked 30-60 minutes after the procedure. You may also be given some anti-inflammatory medication to use for a few days to a week to prevent any significant inflammation. Your ophthalmologist will want to check your drainage angle using gonioscopy 4-6 weeks after the procedure. As mentioned above, some patients will still require eye drops or additional laser treatment even after a successful laser iridotomy.

Laser Peripheral Iridotomy Video

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