Machine vision methods are widely and successfully used for assuring the quality of any produced goods. Many of these methods require the test object’s surface to be either nearly Lambertian or specular. Since transparent materials do not meet these requirements, suitable approaches for the inspection of transparent materials are needed. This paper provides an overview on existing methods for testing transparent objects for enclosed impurities, defects affecting the shape or anomalies of the index of refraction. Besides, possible topics for conducting further research are identified.