What is Astigmatism ? Astigmatism symptoms, Astigmatism causes, Astigmatism diagnosis and treatment. Astigmatism is a type of refractive error caused by the irregularities in the shape of a person’s cornea. In this condition, the eye fails to focus the light equally on the retina leading to blurred or distorted vision. Astigmatism is a common eye condition which usually occurs with myopia or hyperopia and can be easily diagnosed with a simple eye exam. Astigmatism is a refractive error and is not an eye disease or eye health issue. Astigmatism is simply a problem with how the eye focuses light.