Accommodation–Vergence Interactions

Definition

In this context, accommodation refers to the change in the refractive power of the crystalline lens of the eye. A unit of refractive power is the Diopter, which is the reciprocal of the focal length measured in meters. Positive accommodation decreases the focal length of the lens, allowing near objects to be seen clearly, while negative accommodation or relaxation of accommodation increases the focal length for viewing more distant objects. Vergence, or vergence angle, refers to the angle between the lines of sight of the two eyes in the horizontal plane. Clinically, vergence angle is usually expressed in terms of prism diopters. A prism diopter is the deviation of light by one cm at a distance of one meter, and is ∼0.57°. Convergence (Convergent eye movement) is an increase in vergence angle, and occurs when viewing a near object with both eyes. Divergence (Divergent eye movement) is a decrease in vergence angle. Accommodative convergence (AC) is the increase in vergence...