What causes the eye with astigmatism to be out of focus?
In eyes with astigmatism the cornea, the clear dome covering the front of the eye, is not quite perfectly round. The curvature, if measured closely, is a little flatter in one direction (say, horizontally) and a little steeper in the other direction (say, vertically). This difference in curvature causes a difference in focus for lines of different orientations. For example, when looking at the letter “E” on the eye chart, the person with astigmatism may see the vertical line in focus, but the horizontal lines out of focus, or vice versa. In some patients with astigmatism the flattest and steepest corneal curves are oriented at an angle, instead of horizontally and vertically. These people see shadows of blurriness extending at angles from the letters or objects they view. What causes astigmatism? The cause is unknown. Protein in the corneas of people with astigmatism may be more flexible than normal, making the corneas more likely to get out of round. Is astigmatism always a problem? N
