The individual who is predisposed to angle closure has anatomically narrow but still open angles. Narrow angles can be detected by directing the beam of a penlight parallel to the plane of the iris. If there is no shadow nasally, then the angles are most likely wide enough to dilate. Dilation with phenylephrine 2.5% is associated with minimal risk of precipitating angle-closure glaucoma. Systemic medications with anticholinergic side effects should be used with caution in patients with angle closure glaucoma or narrow angles because they cause the pupil to dilate and may precipitate an acute attack of angle closure.