This compact device easily fits in a shirt or clinic jacket pocket. The "Prism Bar" format makes quantifying afferent pupillary defects a simple task. The overall bar is 16.5 cm long, each filter measures 2.5 cm x 3 cm. Optical density values on the six filters are rated as 0.3, 0.6, 0.9, 1.2, 1.5 and 1.8.