Since their development nearly 50 years ago, lasers have revolutionized many fields, particularly medicine. Lasers allow us to easily and safely perform procedures which were once much more invasive, or not possible at all.
A laser is basically a very focused beam of light energy. The color of light emitted by a laser is determined by the type of material used to produce it. This material can be a gas, a liquid, a solid, or a semiconductor such as a diode. When the material inside the laser tube is energized, it produces light of a very specific wavelength, or color. In ophthalmology, lasers range in wavelength from infrared to ultraviolet. The wavelength determines how the laser will affect different cells and tissues within the body. The ability to control the exact amount of energy delivered by the laser makes it the perfect tool to perform precise, delicate surgery within the eye.
The anterior chamber angle is formed where the peripheral cornea and iris meet. At the apex of this angle lies the trabecular meshwork, the sieve-like entrance to the ocular drainage system. Aqueous humor, the fluid which fills the front of the eye, is constantly being created. Anatomy of the eye This fluid must therefore flow out through the trabecular meshwork in order to maintain the proper pressure within the eye. If the drainage system becomes blocked, aqueous humor cannot escape and pressure will build, potentially damaging ocular structures.
In a normal eye there is plenty of space at the angle and the trabecular meshwork is wide open. In patients with narrow angles the iris and cornea are too close together, limiting the ability of aqueous humor to enter the drainage system.
In most cases, narrow angles are a genetically determined condition. Affected individuals are usually hyperopic (farsighted) with shorter than average eyes. Women are affected more often than men, and the condition often worsens with age. Individuals of Asian or Eskimo ancestry appear to be at greater risk for narrow angles.
Plateau iris, another abnormal condition associated with angle narrowing, occurs due to abnormal anatomy in the ciliary body, causing the iris to be pushed too far forward. This condition is less common than that previously described, and will not be detailed here.
Other conditions can occasionally be associated with narrow angles. For example, a very thick, mature cataract can compromise the angle, causing high pressure. This is resolved by cataract surgery.
Chronic IOP elevation: Increased resistance to aqueous humor outflow can lead to a chronic elevation in intraocular pressure, known as chronic angle closure glaucoma. This condition often behaves like the more typical open angle glaucoma, with moderately elevated pressures, no pain, and slow but progressive loss of visual field.
Acute angle closure: In some cases, the trabecular meshwork may become completely blocked by the iris, leading to a fairly rapid rise in intraocular pressure, associated with severe pain, redness, and swelling of the eye along with very blurred vision.
Nausea and vomiting are common, as are colored halos around lights. If not treated urgently, acute angle closure can cause permanent loss of vision. The condition is often precipitated by partial dilation of the pupil. This may occur upon entering a lighted space after being in prolonged darkness, with excercise or excitement, or even with pharmacologic dilation during an eye exam. Individuals with a history of narrow angles should seek medical attention if the above symptoms occur.
As noted previously, aqueous humor is produced by the ciliary body in the posterior chamber of the eye, the space behind the colored iris. This fluid normally passes through the pupil and into the anterior chamber, the space in front of the iris. Aqueous then drains into the trabecular meshwork and out of the eye. However, in narrow angles, fluid cannot move through the pupil normally, due to excessive contact between the iris and lens. Fluid builds up behind the iris, pushing it forward, further narrowing the angle and leading to acute closure in predisposed individuals. This situation is known as pupillary block (see diagram above), and is the most common cause of acute angle closure.
Anatomically narrow angles are treated by a procedure called laser peripheral irodotomy (LPI), performed most commonly today with a YAG laser. The laser is used to create a very small opening in the far periphery of the iris.
Flow of aqueous humor through a peripheral iridotomy The iridotomy is therefore completely within the eye- it is not a hole in the eyeball. This opening allows the aqueous humor to pass freely through the iris and into the trabecular meshwork. An iridotomy acts as a low-resistance”bypass,” giving aqueous a clear pathway into the drainage system. In most cases the iris will actually move slightly backwards after iridotomy, as there is less pressure built up behind it. This deepens the anterior chamber, opening the angle wider, further facilitating the outflow of aqueous humor from the eye. Laser iridotomy is therefore the initial treatment of choice for patients with chronic angle closure. It is also the best means of prophylactically reducing the risk of acute angle closure in patients predisposed to the condition.
If your physician determines that your angles are significantly narrow, putting you at risk for acute angle closure, peripheral iridotomy many be recommended.
Laser iridtomy is a brief, in-office procedure. Many patients are able to drive to and from their appointment alone, though blurry vision may occur after the procedure and a driver may be desired. The actual procedure is described below:
All laser procedures have some risk. Risks of iridotomy include:
The above list of complications is provided for informational purposes. Iridotomy is a very commonly performed procedure which is quite safe. Serious complications are very rare. The risk of any complication is generally outweighed by the risks of not performing the iridotomy. Acute angle closure can be devastating, causing permanent damage to the eye, and is preventable in more than 95% of cases by prophylactic iridotomy. Please discuss all concerns with your surgeon.
If you have any questions about this or any other procedure, please feel free to contact us for more information.