It is impossible to convert 20/20 vision directly into diopters because they are two different measures of sight. However, there is a correlation between the measure of visual acuity (20/20) and the focusing power of corrective lenses (diopters).
- Determine visual acuity
Individuals with 20/20 vision have average visual acuity, which means they see the same detail at a distance of 20 feet as most other people. Optometrists typically use a Snellen eye chart to measure acuity to determine how strong of a correction may be needed.
- Find out the strength of corrections
Ask your optometrist for the number that corresponds to the strength of focus on your lenses. Near-sighted individuals have a number that's expressed in negative diopters, such as -5.00. Corrections for far-sighted people are shown in positive diopters, such as +3.00.
- Consult a diopter to visual acuity conversion chart
Visual acuity does not directly convert into diopters. Lower corrections are usually consistent from one patient to another. For instance, a -1.00 diopter correction usually belongs to a person with 20/40 vision. Corrections higher than six diopters, either negative or positive, may have exponentially lower acuity than lower corrections. These are determined by data collection rather than mathematical formulas, so an acuity chart is necessary for the conversion.