What Is a Narrow Angle Evaluation?

A narrow angle evaluation is a method of evaluating patients presenting with angle closure or potential angle closure glaucoma. 90% of glaucoma cases in the US are open angle, meaning that the space between the iris and cornea is not blocked and the intraocular pressure builds up in the chamber of the eye over several years. Acute angle closure, on the other hand, is a vision emergency caused by a forward displacement of the root of the iris, partially or entirely blocking the angle between the iris and the cornea which normally functions as an irrigation canal.

Signs and Symptoms

• In order for a doctor to perform a narrow angle evaluation, first the doctor must see signs and symptoms that the patient could have angle closure glaucoma. These signs and symptoms include seeing halos or rainbows around lights, eye pain, red eye, high intraocular pressure, nausea, vomiting, headaches, sudden decreased or blurred vision and a pupil that is fixed at a middle dilation and does not respond to light.

Gonioscopy

• Gonioscopy is a method of evaluating how narrow the angle between the iris and the cornea is by directly viewing that space. Normally, the eye's reflections interfere with the ability to view this region, but a gonioscope, or goniolens, is a device that rests directly on the eye's surface and uses mirrors to reveal the area. The doctor then looks for key anatomical structures which are visible if the patient has an open angle, and not visible if the patient has a narrow or closed angle.

Shaffer Grading System

• The visibility of structures seen with a gonioscope is evaluated with the Shaffer grading system. The grades run from 0 to 4, with eyes evaluated a 0 having the greatest danger of closure. If structures toward the back of the eye -- such as the ciliary body band -- are within the angle, the eye is not in great danger of closing.

Van Herick's Method

• Van Herick's method of evaluating angle closure glaucoma requires only a slit lamp, making it a convenient test compared to others that require more sophisticated equipment. The slit lamp is shined into the eye at the edge of the iris, coming in at a 60-degree angle. The eye's reflection of this light results in an image of the slit appearing on the cornea, parallel to the slit on the iris. The doctor evaluates the relative width of the slit on the cornea and the space between the two slits. If the space between the slits is no smaller than half the width of the corneal slit, the angle is open and closure is unlikely. Narrow angles are indicated by a space between slits that is less than a quarter of the width of the corneal slit, which indicates that complete closure is likely or has already occurred.