Test disc used to examine visual acuity under differing lighting conditions

摘要

A test disc is used in a unit for the testing of visual acuity under differing lighting conditions. There is a casing, a test object carrier, on which test patterns are arranged for recognition, and holes allowing bright, directed aperture light to pass through. The two parts of the casing rotate against each other, relative to the central axis. A first neutral density filter is fitted to the upper part, covering an angular region of up to 180 deg . This part of the casing is so constructed, that when the first filter is in front of the visible test pattern, no bright light passes through the holes.