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. [2] X Trustworthy Source American Optometric Association Professional medical organization dedicated to supporting optometrists and improving public eye and vision health Go to source
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. [4] X Research source
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.
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.
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 autorefractors that measure refraction, and the IOLMaster that makes extensive measurements of the interior and exterior of the eye. The IOLMaster is usually used before cataract surgery. [9] X Research source
This method can help to diagnose keratoconus, a disorder that causes irregular astigmatism due to thinning and protruding of the cornea. Your doctor may also use a modern instrument that has a light in the center. The disc is projected onto the cornea, and the doctor will analyze the reflection of the light on your cornea. [11] X Expert Source Rajesh Khanna, MDBoard Certified Ophthalmologist Expert Interview. 11 November 2020.
This method can be helpful in predicting how successful surgery may be in correcting your astigmatism.
