Astigmatism is a vision condition in which light entering the eye is unable to be brought to a single focus, resulting in vision being blurred at all distances.
Astigmatism is one of a group of eye conditions known as refractive errors. Refractive errors cause a disturbance in the way that light rays are focused within the eye. With astigmatism, light rays are focused in such a way that both nearby and faraway objects may appear blurry. Astigmatism often occurs with nearsightedness and farsightedness, conditions also resulting from refractive errors.
If you experience a distortion or blurring of images at all distances, nearby as well as far, you may have astigmatism. Even if your vision is fairly sharp, headache, fatigue, squinting and eye discomfort or irritation may indicate a slight degree of astigmatism. A thorough eye examination by our optometrists, including tests of near vision, distant vision and vision clarity, can determine if astigmatism is present. Astigmatism is not a disease, nor does it mean that you have "bad eyes." Usually, it simply means that you have a variation or disturbance in the shape of your cornea.
What causes astigmatism?
Normally the cornea, the front window of the eye, is smooth (like a baseball) and equally curved in all directions. This causes light entering the eye to be focused equally on all planes, or in all directions. In astigmatism, the front surface of the cornea is curved more in one direction than in the other (like an American football or rugby ball). With the cornea being irregularly shaped, the light hitting the more curved surface comes to a focus before that which enters the eye through the less curved surface. Thus, the light is focused clearly along one plane, but is blurred along the other so only part of anything being looked at can be in focus at any time.
Not all corneas are perfectly curved, just as sets of teeth are seldom perfectly aligned. The degree of variation determines whether or not you will need a correction for the astigmatism. If the corneal surface has a high degree of variation in its curvature, light refraction may be impaired to the degree that corrective lenses are needed to help focus light rays better.
Who develops astigmatism?
Astigmatism is very common. Some experts believe that almost everyone has some degree of astigmatism, often from birth, which may remain the same throughout life. However, only individuals with moderate to highly astigmatic eyes usually need corrective lenses.
The exact reason for differences in corneal shape remains unknown, but the tendency to develop astigmatism is inherited. For that reason, some people are more prone to develop astigmatism than others.
How is it diagnosed?
Astigmatism is diagnosed in the course of a thorough eye examination by our optometrists.
Keep in mind that in children, astigmatism is often not detected during routine eye screenings in school. For this reason, children should be examined by our optometrists as often as recommended.
How is it treated?
If the degree of astigmatism is slight and no other problems of refraction, such as nearsightedness or farsightedness, are present, corrective lenses may not be needed. If the degree of astigmatism is great enough to cause eyestrain, headache, or distortion of vision, prescription lenses will be needed for clear and comfortable vision.
The corrective lenses needed when astigmatism is present are called "toric" lenses and have an additional power element called a cylinder. They have greater light-bending power in one axis or direction than in the others. Precise tests will be made during your eye examination to determine the ideal lens prescription.
Today, contact lenses are also a great option for the majority of those patients with astigmatism. Hard lenses, soft lenses, and even hybrid combination lenses work well. Those that have been told that they could not wear contact lenses in the past due to astigmatism are finding it easier to wear lenses and be happy with clear, comfortable vision.
LASIK and other refractive surgeries are also a great option.
Since there are so many options, our optometrists will help you decide which one of these procedures is best for you.
Astigmatism may increase slowly over time. Yearly eye examinations by our optometrists can help to ensure that proper vision is maintained.