Optical Distortions Of Acrylic Panels 
Local distortion is an easily detected visual imperfection. It is usually caused by the use of improper sanding techniques. Select a straight object at least 0.6 meters beyond the panel and move slowly side to side. Localized distortion actually results in a blind spot (like looking through a magnifying glass), which is most often caused by concentrating sanding to one small area. To remove a distortion, a large area around the distortion must be sanded and "feathered" into the panel. Use a series of sandpapers and remove materials around it to blend the surface. Work across the top of the distortion so you do not make it deeper.
Distortions are also caused by waviness of surfaces, and/or variations in the optical properties of the material itself. In either case, the results are local angular deviation and/or displacement of light rays through the panel.
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