Astigmatism results from a misshapen cornea, the clear front covering of the eye. A normal cornea has a smooth, round curve. In astigmatism, the curve is elongated and greater in one direction than in another, and the shape is often described as bulging, like a football, rather than circular, like a basketball. When light rays pass through such a cornea, they are not refracted, or bent, equally in all directions, and they are focused on several points on the retina, rather than on one point. Vision is distorted for both nearby and faraway objects, and what is seen may be blurred or distorted.
Surgery is one option for correcting astigmatism.
In a procedure called astigmatic keratotomy, incisions are made in a curved pattern to reshape the cornea. In photorefractive keratectomy, a laser reshapes the surface. However, it is probable that neither one would have changed how El Greco painted. The theory that he was astigmatic was advanced in 1913, but scientists now believe that the elongated shapes in his paintings were deliberate, rather than the result either of faulty vision or lenses used to correct it. X-rays show more realistic drawings under his final paintings, and there is no evidence that corrective lenses for astigmatism, which might have produced elongated images in one direction, were available to him in the 16th century.