1 a test performed on a person who has diminished visual acuity to distinguish a refractive error from organic disease. A refractive error may be corrected with glasses, whereas organic disease may signal the development of preventable blindness. Several pinholes, 0.5 to 2 mm in diameter, are punched in a card. The patient selects one and looks through it with one eye at a time, without wearing corrective lenses. If visual acuity is improved, the defect is refractive; if not, it is organic. The pinhole effect results from blocking peripheral light waves, which are most distorted by refractive error.
2 a test to determine the size of the focal spot of an x-ray tube.
3 a test to trace the path of x-ray tube movement.