Most people are familiar with two common refractive errors in the eye: nearsightedness and farsightedness. Surprisingly, there's a third type of refractive error that can give you blurry vision, and it's called astigmatism. It's not an eye disease, but a problem your eye has in focusing light. This causes your vision to be out of focus in multiple ways in a single eye, requiring more than one prescription for correcting your vision.
Many correctable vision problems are caused by abnormal eye anatomy. Very few people have perfectly shaped eyes that facilitate ideal vision. Rather, most people have some degree of abnormal curvature or other anatomical irregularities that cause slight visual changes. Astigmatism is one common form of visual impairment that results from irregular anatomy.
What Is Astigmatism?
The clear front area of the eye is called the cornea, which is important for refracting light rays to direct them onto the retinal surface. Light rays pass through the cornea onto the lens. The lens is flexible, changing shape to further focus the light rays and ensure that they hit the retina. Light must bend at a particular angle to result in clear, focused vision. Any abnormalities in eye structure may cause light to be improperly focused onto the retina, preventing visual sensory cells from processing the images.
Astigmatism occurs when either the cornea or the lens is abnormally curved. It is important to note that nearly everyone has some degree of astigmatism, as ocular structures are rarely perfectly shaped. When the cornea or lens has particularly pronounced curvature, however, light rays fail to focus onto the retina. This leads to blurry vision. Unlike farsightedness or nearsightedness, astigmatism causes blurred vision at any distance. Many people have astigmatism as well as farsightedness or nearsightedness.