Abstract: A system and method for detecting optical defects on a surface of a transparent or semi-transparent structure, tube or article is provided. Defects are identified and analyzed by using a digital camera to capture an image of a target having a pattern of light and dark areas through a portion of the article. The images are processed to enhance the visibility of the defects, and the distribution of the defects as function of their location on the surface of the article is determined. This determination is used as part of a statistical process control method for controlling the level of defects present on the surface of the article.