The Neutral Density Filter Bar allows to easily measure afferent pupillary defects (APD) also called “diminished pupil reaction to light levels”. Provides the filter values: 0.3, 0.6, 0.9, 1.2, 1.5, 1.8 Density Log Units. Each filter is 1.5" (38 mm) square with an overall bar size of 10" by 1.5" (25.3 cm by 3.8 cm). Comes with a handle for easy use and case for storage.