to differentiate between a functional amblyopia from an organic one - the six filters are rated as: 0.3 - 0.6 - 0.9 - 1.2 - 1.5 and 1.8 log unit optical density values - the ND Bar is used in conjunction with the “Swinging Flashlight” test to detect and quantify the extent of any afferent pupillary defect (APD) – size 25.4 x 5.0 cm