Astigmatism is an irregular curvature of the cornea that causes a refractive error in a person's vision. Everyone has this condition to some extent, but only 10 percent of the population has visually significant astigmatism (usually defined as more than one diopter).
Instructions
1. Observe the presenting symptoms of astigmatism. These consist of blurred vision over all distances, eyestrain, fatigue and headaches. Astigmatism frequently occurs with refractive errors such as hyperopic and myopia.
2. Conduct comprehensive eye exams. These tests measure the ability of the eyes to focus and the amount of correction your eyes may require. Astigmatism is a non-spherical refractive error that is more difficult to diagnose because it has both magnitude and orientation whereas a spherical error has only magnitude.
3. Measure the basic visual acuity using a standard eye chart. Visual acuity is expressed as a fraction. A person with 20/40 vision would have to be 20 feet from a chart that a person with standard vision could read at 40 feet.
4. Perform a keratometry. A keratometer determines the cornea's curvature by reflecting a circle of light from the cornea and measuring the reflection. A corneal topography provides a more accurate description of the cornea's shape.
5. Determine the refraction. A phoropter is a series of lenses, and a retinoscope is a handheld lighted instrument that the ophthalmologist combines to evaluate the eye's focusing ability. The patient's responses refine the refractive value.
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