1. An apparatus for assessing visibility through an optical material, the apparatus comprising: an imaging system including a target and a camera located and oriented for acquiring digital images of the target through the optical material, wherein the imaging system is adapted to capture multiple discrete digital images at different times; a system for exposing the optical material to one or more environmental conditions; and a processing system including programming for determining intensity of the target in the digital images, the programming further including operations relating the intensity of the target to a visual acuity index to assess the visibility through the optical material, wherein the processing system includes programming for determining the intensity of the target in the discrete digital images to assess changes in visibility through the optical material over time.