20/20 vision is measured using a standardised eye chart at a set distance. The test checks how small a letter size you can read clearly, one eye at a time and then together.
The testing set-up
Clinics use Snellen charts or digital equivalents. You read down the lines until the letters become too difficult, wearing your usual glasses if appropriate.
- The chart is usually placed twenty feet away or optically simulated.
- Each line corresponds to a specific visual acuity level.
- The smallest line you can read reliably defines your acuity score.
- Testing is done first without and then with lenses when needed.
- Children may use matching pictures or letters instead of reading aloud.
What the results mean for you
Your acuity helps decide whether you need glasses or a new prescription. It also indicates whether your sight meets driving or occupational standards.
- Improvement with lenses suggests simple refractive error.
- Poor acuity that does not improve may signal eye disease.
- Some jobs require better than 20/20 or specific visual fields.
- Regular checks track changes and guide treatment timing.
- Ask for a copy of your results if you need them for licensing forms.
