How do you convert a vision reading from 20/20 type to -1 type?

Question: I know my eye sight is -8 in both eyes and my friends never know what I'm talking about. They'll say things like 20/100 for their eye sight. Do you know how to convert from one to the other?

Answer: You really can't convert them directly from one to the other. The -8.00 that you are referring to is what is called your refractive error. The 20/100 you are referring to is referring to actual visual acuity. Of course, the worse your refractive error the worse your visual acuity will be. But visual acuity is not one to one related to refractive error. Other things than refractive error can influence ones visual acuity. For instance pupil size can influence visual acuity. One person with say a -2.00 refractive error with a 2 mm diameter pupil may have significantly better visual acuity than another with a -2.00 refractive error but a pupil size of 6 mm. If I had to guess, though, I would say your visual acuity with a -8.00 refractive error would range from 20/400 to 20/800. Only way to know for sure would be to have your visual acuity tested. Hope this helped.

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