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How to measure astigmatism



Astigmatism is a common eye disease that causes blurred vision. It occurs when your cornea is more elongated or football-shaped than round. Astigmatism can be diagnosed by your optician or ophthalmologist with a comprehensive eye examination. It can be corrected with glasses, contacts, or sometimes surgery – but measuring the shape of your cornea is important to getting the right lens prescription. [1] Astigmatism is usually measured by a series of eye examinations, some of which are common methods and others that may apply only in certain circumstances.

[ Edit ] Step

[ Edit ] Using the Standard Measurement Tools

  1. Perform Visual Acuity Test. Stand where your doctor tells you at your ophthalmologist's office and look at a chart with numbers and letters on the wall. Cover one eye and read the lines of text to the smallest line you can clearly read, then repeat this with your other eye covered. This test for myopia (myopia) and hyperopia (myopia) and astigmatism. [2]
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    • Astigmatism accompanies myopia or hyperopia 50% of the time. Blurred vision can be caused by astigmatism or one of these other common conditions.
    • The results will be listed as a fraction, for example 20/20. 20/20 is normal visual acuity. The first number is the distance between you and the chart. The second number is the size of the letters on the last line you can read compared to normal visual acuity. For example, someone with 20/40 vision must be 20 meters from something that can be read by someone with normal vision. [3]
  2. Measure the curve of your cornea with a keratometer. A keratometer is the instrument your ophthalmologist can use to measure the curve of your anterior cornea (the anterior surface of the cornea). [4] Sit with your chin on your chin rest and look straight ahead in the instrument with one eye and then others, when asked by your doctor. The keratometer glows a bright circle on your cornea and measures how it reflects on the surface of your cornea.
      Measure Astigmatism Step 2 version 2.jpg
    • This is a particularly important test to get contact lenses that fit properly. [19659010] Although this method has its limitations, it is still the usual way to measure astigmatism. [5]
  3. Use refraction to measure astigmatism. Sit straight up and look ahead while your doctor places a retinoscope in front of your eyes. The Retinoscope is a small, hand-held instrument that measures light refraction in the eye. Your doctor will move a large machine with lenses (a phoropter) in front of your eyes that either clarifies or obscures your vision, which measures how your eyes focus light. You must tell your doctor if each lens makes your vision better or worse. [6]
      Measure Astigmatism Step 3 Version 2.jpg
    • The refractive test helps determine the location of the irregular shape of the cornea. This will be called the "axis" of a corrective lens prescription.
    • Be honest with your doctor during these tests – although the technique improves, your feedback will still help determine the results of your eye examination.
  4. Understand your prescription for astigmatism. After your eye examination, your doctor will give you a prescription for glasses or contact lenses to fix your astigmatism. The prescription will usually have three digits – the first one refers to whether you are visually impaired or impaired, and the last two refer to your astigmatism. [7]
      Measure Astigmatism Step 4 Version 2.jpg
    • The second number is for "cylinder", which is a measure of how flat or irregular your cornea is. This is measured in diopters. Most people with astigmatism have between 0.5-0.75 diopters; you probably need prescription lenses for a diopter measurement of 1.5 or higher.
    • The third number is for "axis" and goes from 0 to 180, which is a degree measurement of where on your cornea astigmatism is.

[ Edit ] Using other measurement options

  1. Use a corneal topograph for more accurate measurements. A topograph is a newer version of the keratometer. [8] Your doctor will let you sit at a table and look into a bowl. The inner surface of the bowl is covered by a pattern of concentric rings. A digital camera sits at the bottom of the bowl and maps the surface of the cornea by measuring the reflected pattern in the eye. This basically creates a contour map on your eye, and it is an excellent technique for measuring irregular astigmatism. [9]
      Measure Astigmatism Step 5 version 2.jpg
    • Most corneal topography tests measure 8,000 to 10,000 points on the cornea, making it the most accurate keratometry test.
    • Other advanced ways of measuring astigmatism include autofractors that measure refraction and IOLMaster that make extensive measurements of the inner and outer eye. IOLMaster is usually used before gray cataract surgery. [10]
  2. Try a placido disc for irregular astigmatism. The Placido is an old-fashioned, handheld device shaped like a giant club. The disc has several sets of concentric circles painted on one side and used to measure the regularity of the surface of your cornea. Your doctor holds the disc up to his own eye with the rings facing you and they look into the eye. Sit still and look straight ahead. The image of your cornea reflects back, and where there is an irregular shape it makes the concentric rings look distorted to your doctor. [11]
      Measure Astigmatism Step 6 Version 2.jpg
    • This old-fashioned method can help diagnose keratoconus, a disorder that causes irregular astigmatism due to thinning and ejection of the cornea.
  3. Use a Scheimpflug device to measure the posterior cornea. The shape of your posterior cornea (the posterior surface of the cornea) can affect the severity of your astigmatism. [12] Keratometry can only measure the front of your cornea, but Scheimpflug imaging uses tomography to get more accurate readings of how thick your cornea is and how the back of it looks. [13]
      Measure Astigmatism Step 7.jpg
    • This method can be helpful in predicting how successful surgery can be to correct your astigmatism. [19659038] [ Edit ] Tips
      • More than one eye test is usually done to measure astigmatism. An ophthalmologist or optician will perform a series of tests in his office with various equipment. [15]
      • Most astigmatisms can be treated by using prescription glasses or contact lenses. Depending on the severity of your astigmatism, laser operations such as LASIK can also improve your vision. In severe cases, as with keratoconus, a corneal transplant surgery or the use of rigid corneal-forming corrective lenses may be necessary. [16]

      [ Edit ] Video

      [ Edit ] References

      1. [1945 http://www.aoa.org/patients -and-public / eye-and-vision-problem / gossary-of-eye-and-vision-conditions / astigmatism? sso = y # 2
      2. http://www.aoa.org/patients-and-public/eye-and-vision-problem/gossary-of-eye-and-vision-conditions/ astigmatism? sso = y # 2
      3. http://www.aoa.org/patients-and-public/eye-and-vision-problem/gossary-of-eye-and-vision-conditions/ astigmatism? sso = y # 2
      4. http://www.aoa.org/patients-and-public/eye-and-vision-problem/gossary-of-eye-and-vision-conditions/ astigmatism? sso = y # 2
      5. http://www.ophthalmologyweb.com/Tech-Spotlights/26530-Keratometry-Focusing-on-Astigmatism/
      6. http: //www.aoa .org / patients-and-public / eye-and-vision-problems / glossary-in-eye-and-vision-conditions / astigmatism? sso = y # 2
      7. https://www.aao.org/eye-health/diseases/ what-do-astigmatism-measurement-means
      8. http: // www. aoa.org/patients-and-public/eye-and-vision-problem/gossary-of-eye-and-vision- conditions / astigmatism? sso = y # 2
      9. http://www.ophthalmologyweb.com/Tech-Spotlights/26530-Keratometry-Focusing-on-Astigmatism/
      10. http: //www.ophthalmologyweb .com / Tech-Spotlights / 26530-Keratometry-Focusing-on-Astigmatism / strong19659056vard ↑ http://phisick.com/item/placidos-disk-for-astigmatism/
      11. https: / /www.ncbi.nlm.nih.gov/pubmed/25162757
      12. http://iovs.arvojournals.org/article.aspx?articleid=2212759
      13. https: // www .eyeworld.org / article-review-of – contribution-of-posterior-corneal-astigmatism-to-total-corneal-astigmatism-
      14. [1945 http: //www.mayoclinic .org / diseases-conditions / asti gmatism / diagnosis treatment / diagnosis / dxc-20253081
      15. https://www.aao.org/eye-health/diseases/what-do-astigmatism-measurements-mean

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