Myopia is only one type of refractive error, but there are others such as farsightedness and astigmatism. Myopia is defined as a condition in which parallel light rays pass through the refractive system of the eye with relaxed regulation and are focused in front of the retina. This means that the far point of the human eye is shifted closer to the retina and is called myopia. Myopia is characterized by a lack of clarity in the distance, but can be corrected with a concave lens. 300 degrees or less of myopia is mild myopia, 300 degrees to 600 degrees of myopia is moderate myopia, and more than 600 degrees of myopia is called high myopia.