What it means and why
Visual acuity records how well someone resolves detail under a particular test setup. The chart, distance, lighting and whether glasses were worn all matter. It is a test result, whereas a prescription records optical correction.
Common notations such as 6/6, 20/20 and decimal 1.0 describe similar reference acuity in their respective systems. They are not lens powers and cannot be converted into SPH by multiplying a number.
A worked example
Teaching scenario: two people read the same chart line while wearing glasses, but one has much stronger lenses. Their corrected acuity matches in that test; their prescriptions do not. To compare visits, ask whether the results were unaided, with existing glasses or with the test correction.
What it does not tell you
A good chart score does not assess every aspect of vision or rule out eye disease. Contrast, visual field and eye health require other parts of an examination.
THINK IT THROUGHCan a chart score tell you which lens power to order?
No. Acuity describes performance in a test; refraction and fitting provide different information.
Sources & reading notes
Page updated:
- AOP · Your prescription explained ↗ Professional body guidance
Explains terminology and dispensing practice; it is not a head-to-head product trial.
- AAPOS · Vision screening ↗ Professional body guidance
Explains terminology and dispensing practice; it is not a head-to-head product trial.