How to Measure Astigmatism
Perform the Visual Acuity Test., Measure the curve of your cornea with a keratometer., Use refraction to measure astigmatism., Understand your astigmatism prescription.
Step-by-Step Guide
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Step 1: Perform the Visual Acuity Test.
At your eye doctor’s office, stand where your doctor tells you and look at a chart of 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 tests for myopia (near-sightedness) and hyperopia (far-sightedness), as well as astigmatism.Astigmatism accompanies myopia or hyperopia 50% of the time.
Blurry vision could be caused by astigmatism or one of these other common conditions.
The results will be listed as a fraction, such as 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 instance, someone with 20/40 vision has to be 20 feet from something that can be read at 40 feet (12.2 m) by someone with normal vision. -
Step 2: Measure the curve of your cornea with a keratometer.
A keratometer is the instrument your eye doctor can use to measure the curve of your anterior cornea (the front surface of the cornea).Sit with your chin on the chin rest and look straight ahead into the instrument with one eye then the other, when prompted by your doctor.
The keratometer shines a circle of light onto your cornea and measures how it reflects over your cornea’s surface.
This is an especially important test for getting contact lenses that fit correctly.
Though this method has its limitations, it’s still the standard way of measuring astigmatism., Sit up straight and look forward while your doctor places a retinoscope in front of your eyes.
The retinoscope is a small, handheld instrument that measures light refraction on the eye.
Your doctor will move a large machine with lenses (a phoropter) in front of your eyes that either clarify or obscure your vision, which measures how your eyes focus light.
You will have to tell your doctor whether each lens makes your vision better or worse.The refraction test helps to establish the location of the irregular shape of the cornea.
This will be called the "axis" in a corrective lens prescription.
Be honest with your doctor during these tests – even though technology is improving, your feedback still helps determine the outcomes of your eye exam. , After your eye exam, your doctor will give you a prescription for glasses or contact lenses to help fix your astigmatism.
The prescription will usually have three numbers – the first one relates to if you’re near-sighted or far-sighted, and the last two relate to your astigmatism.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 the astigmatism is located. -
Step 3: Use refraction to measure astigmatism.
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Step 4: Understand your astigmatism prescription.
Detailed Guide
At your eye doctor’s office, stand where your doctor tells you and look at a chart of 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 tests for myopia (near-sightedness) and hyperopia (far-sightedness), as well as astigmatism.Astigmatism accompanies myopia or hyperopia 50% of the time.
Blurry vision could be caused by astigmatism or one of these other common conditions.
The results will be listed as a fraction, such as 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 instance, someone with 20/40 vision has to be 20 feet from something that can be read at 40 feet (12.2 m) by someone with normal vision.
A keratometer is the instrument your eye doctor can use to measure the curve of your anterior cornea (the front surface of the cornea).Sit with your chin on the chin rest and look straight ahead into the instrument with one eye then the other, when prompted by your doctor.
The keratometer shines a circle of light onto your cornea and measures how it reflects over your cornea’s surface.
This is an especially important test for getting contact lenses that fit correctly.
Though this method has its limitations, it’s still the standard way of measuring astigmatism., Sit up straight and look forward while your doctor places a retinoscope in front of your eyes.
The retinoscope is a small, handheld instrument that measures light refraction on the eye.
Your doctor will move a large machine with lenses (a phoropter) in front of your eyes that either clarify or obscure your vision, which measures how your eyes focus light.
You will have to tell your doctor whether each lens makes your vision better or worse.The refraction test helps to establish the location of the irregular shape of the cornea.
This will be called the "axis" in a corrective lens prescription.
Be honest with your doctor during these tests – even though technology is improving, your feedback still helps determine the outcomes of your eye exam. , After your eye exam, your doctor will give you a prescription for glasses or contact lenses to help fix your astigmatism.
The prescription will usually have three numbers – the first one relates to if you’re near-sighted or far-sighted, and the last two relate to your astigmatism.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 the astigmatism is located.
About the Author
Amanda Flores
Committed to making creative arts accessible and understandable for everyone.
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