A demonstration of the refractive changes occurring in the eye when accommodating. The subject observes a target monocularly (such as a simple point of light) through a Scheiner's disc (an opaque disc with two pinholes separated by a distance less than the pupil diameter). It will be seen singly at only one distance where the eye is focused, because target and retina are then conjugate. If the eye accommodates, two points of light are seen. The principle of this experiment is incorporated in several refractometers. See Fig.D6; optometer, infrared; optometer, Young's.