My contact lens prescription is -2.20. What is the diopter?!

Best Answer - Chosen by Voters

2.20 doesn't exist, it's either -2.00 or -2.25. In any case those are your diopters. if by "diopter" you mean something like 20/20, then you're talking about visual acuity which is totally a different thing and can't be derived from your diopters. To determine your visual acuity there's no other way than to read the Snellen chart which all doctors have (it's the chart with big and small letters).

Diopters are prescription powers to eye docs. You can have diopters of sphere and diopters of cylinder (astigmatism). If it just says -2.00 or -2.25 that is diopters of sphere. If it is -2.00 -2.25x180, the -2.00 is sphere and the -2.25 is the cylinder or the astigmatism power.

Eye docs do powers of quoter and 1/6 steps for glasses, but for contacts they are only quarter steps. So in glasses you could have -2.00, -2.12, -2.25, -2.37, -2.50 etc, but normally we dont do 1/6 steps.

4th year optometry student, 7 months until graduation!!

Not really answering your question but the optometry student that answered your question needs to know this before he graduates: 0.12 is approximately 1/8 not 1/6. I worked in an optical shop where they called them twelfths. That was also not correct. One half of one quarter is one eighth. You should have learned that in seventh grade.

optometrist

There is no such thing as - 2.20 in glasses or contacts...that has to be - 2.00 or - 2.25

Whichever it is...is what the diopter is.

- 2.00 is 2 diopters....- 2.25 is 2 1/4 diopters

Optician

Fooprinc is right. So glad to see the spaceman admits there is a use for eye exams and snellen charts. Call your eye doctor and ask him/her to explain your prescription to you. That is one of the things they get paid for.

No such thing as -2.20, there is -2.25.

You dioptre is -2.25.

Good luck

Eye care specialist.

Maybe you got 20/20.