Visual Acuity Testing (Snellen Chart)
This calculator is intended as a convenient screener for visual acuity to be used on a mobile device and should not be used as a replacement for in-office testing. Evidence for smartphone apps for Snellen visual acuity is limited, and currently no app has been found to be accurate to within at least one line of formal visual acuity testing (and further validation is required).
- Ensure proper room lighting and set phone brightness to 100%.
- Hold the screen 4 feet (1.2 m) from the patient (approximately the end of a standard hospital bed if patient is sitting upright).
- Test each eye independently. The patient should completely cover the opposite eye.
- See Pearls/Pitfalls for further instructions.
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