Narrow angles of the eye describe an anatomical configuration where the iris lies close to the cornea. This proximity narrows the space where internal fluid must drain to maintain proper eye pressure. Identifying this structure is an important finding in a routine eye examination, as it represents a potential risk factor, though it is not a disease state in itself.
Understanding the Eye’s Drainage System
The eye maintains its shape and internal environment through a continuous flow of aqueous humor, a clear fluid constantly produced by the ciliary body behind the iris. The aqueous humor circulates through the pupil and fills the anterior chamber, the space between the iris and the cornea.
The fluid must exit the eye at the same rate it is produced to keep the intraocular pressure (IOP) within a healthy range. Drainage occurs at the iridocorneal angle, the junction where the outer edge of the iris meets the inner surface of the cornea. This angle functions like a sink drain for the eye’s internal plumbing.
The primary drainage structure is the trabecular meshwork, a spongy tissue located within this angle. The aqueous humor filters through this meshwork and flows into Schlemm’s canal, which returns the fluid to the bloodstream. If the angle is wide, the meshwork is fully exposed, allowing unrestricted outflow and stable eye pressure.
In a person with narrow angles, the peripheral iris is positioned closer to the cornea, partially obscuring the trabecular meshwork. Although the fluid may still drain sufficiently, the reduced space makes the eye structurally susceptible to future blockages. This anatomical variation sets the stage for a mechanical obstruction of the drainage system.
The Progression to Angle Closure Glaucoma
Having a narrow angle is initially classified as a primary angle closure suspect, meaning the drainage pathway is anatomically restricted but still functioning normally. The risk arises when the iris shifts forward and physically blocks the trabecular meshwork, an event termed angle closure. This blockage prevents the aqueous humor from exiting, causing a rapid or gradual buildup of fluid and pressure.
The most common mechanism for this blockage is pupillary block, often triggered by the pupil dilating in dim light or due to certain medications. When the pupil enlarges, the iris tissue thickens at its periphery, pushing it against the cornea and sealing off the drainage angle. This causes a sudden, steep rise in IOP, known as acute angle closure, which is a medical emergency.
Sustained, elevated IOP damages the optic nerve, which transmits visual information to the brain. This nerve damage results in a progressive and irreversible loss of vision, a condition called angle closure glaucoma. The risk of developing this condition is relatively low for most people with narrow angles.
Angle closure can also progress slowly over time, leading to chronic angle closure glaucoma. In this slower process, repeated minor blockages or sustained pressure fluctuations cause the iris to form permanent adhesions, or scar tissue, onto the trabecular meshwork. This scar tissue permanently closes the drainage angle, leading to a steady, silent rise in eye pressure and subsequent optic nerve damage.
Detecting and Treating Narrow Angles
A person experiencing an acute angle closure episode may have severe symptoms requiring immediate attention. These can include:
- Intense eye pain
- Headaches
- Blurred vision
- Seeing rainbow-colored halos around lights
- Systemic reactions such as nausea and vomiting due to the sudden pressure increase
Narrow angles are typically identified during a comprehensive eye examination, even before any symptoms appear. The standard procedure for assessing the drainage angle is gonioscopy, where a specialized mirrored contact lens is placed on the eye. This allows the eye care professional to view the angle structures directly and precisely measure the angle’s width and the visibility of the trabecular meshwork.
For individuals identified as having narrow angles, the primary preventative treatment is often Laser Peripheral Iridotomy (LPI). This outpatient procedure uses a laser to create a microscopic hole in the outer edge of the iris. The hole acts as an alternative route for aqueous humor flow between the front and back chambers of the eye.
Creating this passage relieves the pressure difference that causes the iris to bow forward and block the drainage angle. Equalizing the pressure causes the peripheral iris to fall back, opening the angle and restoring fluid outflow. In some cases, removal of the eye’s natural lens through cataract surgery can also deepen the anterior chamber, effectively widening the angle and reducing the long-term risk of closure.