A wiper assembly for cleaning optical surfaces. The structure comprises a pneumatically activated wiper element including a wiping means (20) connected to a spring member (17) disposed within a cylinder (16). The wiper element is actuated by air pressure generated by a pumping means (12). The wiping means is connected to an end of a piston rod (19) which passes longitudinally through the cylinder. When activated, the wiping element moves across an optical surface to be cleansed, and at a conclusion of its return stroke, has removed during its simple return stroke, frost, hydrocarbons, entrained particulate material and moisture from the optical surface.