Understanding Astigmatism

Astigmatism causes difficulties in seeing fine detail. In some cases vertical lines and objects such as walls may appear to the patient to be leaning or at a slant. Astigmatism can be often corrected by glasses with a lens that has different radii of curvature in different planes (a cylindrical lens), contact lenses, or refractive surgery. Astigmatism is quite common and according to studies show that about one in three people suffers from the condition. The prevalence of astigmatism does increase with age. Although a person may not notice mild astigmatism, higher amounts of astigmatism may cause blurry vision, squinting, asthenopia (eye strain caused by the inner muscles of the eye tightening), irritation, discomfort, fatigue or headaches.

 

 

So what is astigmatism? The formal definition of astigmatism is one where rays that propagate in two perpendicular planes have different foci, or image points. More simply put, astigmatism occurs whenn the front surface of the eye, the cornea, has an abnormal curvature. Astigmatism is one of a group of eye conditions known as refractive errors. And one of the most prevalent. These refractive errors cause a disorder in the way that light rays are focused within the eye. Astigmatism often occurs with nearsightedness and farsightedness, conditions also resulting from refractive errors. Astigmatism is not a disease nor does it mean that individuals with astigmatism have "bad eyes." It simply means that there is a variation or disturbance in the shape of the cornea.

 

Normally the cornea is very smooth, proportianately curved in all directions and light coming into the cornea is equally focused on all planes and/or in all directions. In astigmatism, the front surface of the cornea is curved disproportionately resulting in distorted vision causing images to appear wavvy or leaning. The distortion results because of an inability of the eye to focus light rays to a point. If the corneal surface has a high degree of variation in curvature, the refraction of light may be impaired to the degree that corrective lenses are needed to help focus light rays better. At any time, only a small proportion of the rays are focused and the remainder are not, so that the image formed is always blurred. Usually, astigmatism causes blurred vision at all distances. Some people with very high degrees of astigmatism may have cornea problems such as keratoconus, a degenerative disorder of the eye in which structural changes within the cornea cause it to thin and change to a more conical shape than its more normal gradual curve.

 

Astigmatism is extremely common and some experts say that almost everyone has some degree of astigmatism, often from birth, which may remain unaltered throughout life. The exact reason for differences in corneal shape remains unknown, but the tendency to develop astigmatism is believed to be inherited. For that reason, some people are more prone to develop astigmatism than others.

 

There are a number of tests conducted by ophthalmologists, optometrists and physicians during eye examinations to determine the existence of astigmatism and to pinpoint the amount and axis of the astigmatism. A Snellen chart or other eye charts can assist in revealing astigmatism. A keratometer may also be used to measure the curvature of the steepest and flattest meridians in the cornea's front surface. A corneal topographer may also be used to obtain a more accurate measurement of the shape and curvature of the cornea. An autorefractor or retinoscopy may provide an objective estimate of the eye's refractive error and the use of Jackson cross cylinders in a phoropter may be used to refine those measurements.   An alternative technique with the phoropter requires the use of a "clock dial" or "sunburst" chart to determine the astigmatic axis and power.

 

If you are experiencing blurry vision, involantary squinting, discomfort, irritation, fatigue or headaches, this could very well be caused by astigmatism or any number of other refractive errors. To best pinpoint and measure the error, please visit your local optometrist or opthamologist for an eye examination. 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. Upon further examination and analysis, the phyisician will be in position to prescribe the necessary corrective measure to fix the error.

For additional information or to schedule an Eye Examination, please contact us at (866) 611-7556.