Narrow Angles

“Narrow angle” refers to the shallow space between the cornea at the front of the eye and the coloured iris that lies just behind the cornea. You might be thinking “What does that have to do with anything?” Well the width of the angle is imperative for numerous reasons the most important of which is proper eye functioning.

A nutrient-rich clear fluid is constantly being produced in the front part of our eyes. The fluid also known as aqueous humor circulates and nourishes the internal tissues before being drained from the eye. The actual drainage opening for the aqueous is formed by the juncture of the cornea and the iris. This drainage angle in the eye can be illustrated by visualizing an ocean clam – that’s right a mollusk. The degree to which a clam is open or closed depends on the angle formed between its upper and lower shells. When the clam is cracked open only a small amount for the sake of illustration think of this opening as a ‘narrow angle’. Likewise if the clam is wide open think of it as an ‘open angle’.

In the eye the cornea and iris represent the upper and lower clamshells respectively. At the point where these two tissue layers join together an angle is formed called the drainage angle. In most people this tissue angle is wide open (think of the open clam) and the aqueous fluid has the opportunity to flow out of the drain unimpeded. However in a smaller percentage of the population the drainage angle is very narrow or nearly closed so the drainage of the aqueous becomes problematic. In this case the eye pressure can rise – sometimes to a dangerously high level – often leading to vision loss and a painful attack. Known as angle closure glaucoma this can occur in two forms.

An acute attack is most likely to occur in dim light when the iris dilates and crowds into the angle. The pressure can build up rapidly within an hour causing increasingly harsh eye pain and headache along with nausea and at times even vomiting. Other symptoms include blurry vision visual rainbows or halos and red eye. Permanent visual loss may occur within hours if not treated promptly.

With chronic angle-closure a series of small attacks takes place over months to years. During each attack small sticky attachments tend to form which causes the iris to adhere to the cornea. They create partial blocks in the angle that can eventually become quite extensive. Some people experience periodic eye aching but usually symptoms are mild or non-existent. Unfortunately because of this you may not be aware of a problem until considerable peripheral vision is lost.

How to Detect if You Have a Narrow Angle

In order to determine the ‘angle of the eye’ a procedure known as gonioscopy is performed. The eyes are anesthetized with eyedrops and using a special biomicroscope for viewing a gonio lens is placed onto the cornea. This lens has mirrors that allow your eye care practitioner to inspect the drainage area and determine whether your angle is wide narrow or closed.

Treatment for Narrow Angles

For people with narrow angles who are at risk for chronic or acute angle closure attacks a procedure known as a laser iridotomy is performed. Laser iridotomy involves creating a tiny opening in the peripheral iris in order to facilitate the drainage of aqueous out of the eye. This procedure takes only a few minutes and requires no sedation.