A subjective method of detecting ametropia in which a thin rod held near the eye is moved across the pupil while the subject fixates a distant light source. The rod casts a shadow on the retina if the eye is ametropic. This shadow will appear to move with the rod in myopia and opposite to the movement of the rod in hyperopia. By moving the rod across the pupil in different meridians, astigmatism can be explored. No shadow is seen in emmetropia.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann