The applications of plastic products in the areas of medical science, computer technology and optics demand high quality and defect free products. The medical products such as implanted lenses to correct cataracts (opacity of the lens of the eye, causing partial or total blindness), contact lenses etc. need to be cmpletely defect free. The injection molded compact disc (CD) substrates of polycarbonate also require to be defect free as well as stress free. The retardation of the optical beam has to be less than 50 nm for single pass in the CD ROM and for erasable magneto-optical disk the retardation needs to be even lower in magnitude. Many optical components also require to be defect free and stress free. In this present investigation, a well known optical birefringence technique is used to study the stresses and microscopic defects such as foreign matter, voids, cracks, bubbles, inclusions, gels, etc. in these products using a commercially available polariscope.