It is essential to know whether astigmatism is internal or corneal to determine the best contact lens. What is astigmatism? It is best demonstrated on a corneal topography — such as Dr. Wallach does on every patient — in its most common form as points of elevation on the corneal surface. The less common form of astigmatism is when the points of elevation are on the lens surface inside the eye. Dr. Wallach patiently works through the process of choosing and modifying the astigmatic contact prescription. Bifocal lenses are also available to correct astigmatism.