How to understand it
Record which eye, test distance and whether correction was worn. Acuity is one part of vision and does not describe every aspect of eye health.
An example
20/20 and 6/6 express comparable chart ratios in different distance units. Neither tells you an SPH value.
A common mix-up
Do not convert a chart score directly into a glasses prescription.
See the idea in a full guide →
Sources & verification
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