How to Convert Eye Grade to Contact Lens Grade

Most people know that 20/20 vision is a perfect eye grade, but few people know how this score relates to the strength of contact lenses. The conversion of visual acuity to the corrective power of a lens requires basic math. Vision scores are written as 20/20 or 20/60, while contact lens strengths are written in diopters as +0.25, or -1.00. About 1/4 diopter, which is the measure of where a lens focuses light, is added to a lens' strength for every increment of 10 that the denominator of your visual acuity is over 20.

Instructions

• 1

  Find out what your visual acuity score is for each eye. You can do this by seeing an optometrist, or by trying to read the visual acuity chart at home.

• 2

  Subtract the numerator of your visual acuity score from the denominator of the visual acuity score of one of your eyes. Write down the result of this subtraction.

• 3

  Divide the number found in the previous step by 10. Write this number down.

• 4

  Multiply 1/4 by the number that you found in the previous step.

• 5

  Repeat the conversion process, this time using your visual acuity score for your other eye.