Narrow angles describe an anatomical configuration where the iris lies unusually close to the eye’s natural drainage system. This proximity restricts the flow of fluid, which can lead to a dangerous increase in internal eye pressure. Narrow angles are a major predisposing factor for angle-closure glaucoma, a serious disease that can cause rapid and irreversible vision loss. Early identification of this structural abnormality is important for preventing damage to the optic nerve.
Understanding the Eye’s Drainage System
The eye continuously produces a clear fluid called aqueous humor, which nourishes the lens and cornea and maintains the eye’s internal shape. This fluid is produced by the ciliary body, located behind the iris, and flows through the pupil into the anterior chamber. The fluid must then drain out of the eye at the “angle,” the junction where the iris meets the cornea.
The drainage structure at this angle is called the trabecular meshwork, a spongy tissue that filters the aqueous humor before it returns to the bloodstream. In a healthy eye, this angle is wide and open, allowing for a balanced flow of fluid. When the angle is narrow, the iris is positioned too close to the trabecular meshwork, reducing the space available for fluid to exit. This crowded anatomy means the iris can easily block the drainage system, trapping the fluid inside the eye.
The Spectrum of Angle-Closure Glaucoma
The most serious consequence of a narrow angle is angle-closure glaucoma, which occurs when the peripheral iris completely blocks the trabecular meshwork. This blockage prevents the aqueous humor from draining, leading to a sudden spike in intraocular pressure (IOP). This rapid pressure rise can quickly damage the optic nerve.
This condition manifests in two primary ways. The first is acute angle-closure, which is a medical emergency. Symptoms include severe eye pain, blurred vision, redness, headache, and sometimes nausea or vomiting. The sudden, high pressure rise, often exceeding 40 millimeters of mercury (mm Hg), can cause permanent vision loss within hours if not immediately treated.
The second presentation is chronic angle-closure, which is often silent and progresses slowly, similar to open-angle glaucoma. In this form, the iris intermittently contacts the drainage meshwork, causing gradual scarring and permanent adhesions called peripheral anterior synechiae. This slow obstruction causes a gradual, asymptomatic rise in IOP, leading to optic nerve damage and field loss that the patient may not notice until the disease is advanced.
Identifying Narrow Angles
Detecting a narrow angle before it progresses to a full angle-closure episode is a primary goal of routine eye examinations. The gold standard for directly viewing the eye’s drainage structure is gonioscopy. During this test, the eye care professional places a special mirrored contact lens on the anesthetized eye to visualize the angle and determine if it is open or occludable.
Complementary to gonioscopy are advanced imaging techniques that provide cross-sectional pictures of the anterior segment. Anterior Segment Optical Coherence Tomography (AS-OCT) uses light waves to create high-resolution images, precisely measuring the space between the iris and the cornea. Ultrasound Biomicroscopy (UBM) uses high-frequency sound waves to image the angle, which can be useful when the cornea is cloudy. These tools help confirm the diagnosis and monitor anatomical changes.
Treatment and Prevention Strategies
The primary treatment for a diagnosed narrow angle is prophylactic, meaning it prevents a future angle-closure attack. The most common intervention is Laser Peripheral Iridotomy (LPI), which is quick and performed in the doctor’s office. LPI uses a laser, often a YAG laser, to create a microscopic opening in the outer edge of the iris.
This tiny hole equalizes the pressure between the front and back chambers of the eye, eliminating the pressure difference that pushes the iris forward. Allowing the aqueous humor to flow freely through this new opening, the peripheral iris relaxes and moves backward, widening the drainage angle. This widening unblocks the trabecular meshwork, reducing the risk of a sudden pressure spike. If the angle remains narrow or a cataract is present, surgical removal of the eye’s natural lens (lens extraction) may be considered, as removing the bulky lens deepens the anterior chamber and opens the angle.