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    Patent Pending

    Visual Acuity Testing (Snellen Chart)

    Assess binocular and monocular visual acuity.

    IMPORTANT

    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). Variation in screen resolution and text size may impact accuracy.

    INSTRUCTIONS

    • 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.
    When to Use
    Pearls/Pitfalls
    Why Use

    To assess binocular and monocular visual acuity in cooperative patients.

    • Patients over the age of 40 may have presbyopia and often require reading glasses; thus, their near-vision test results may be unreliable if the test is administered without reading lenses.

    • Alternate charts exist for illiterate patients or young children, but have limited studies evaluating their use in smartphones.

    • While the Snellen chart is the most widely used method of testing visual acuity in clinical practice, it is not without its pitfalls, including difficulty with standardization of the chart, as well as test-retest reliability.

    Instructions for Use:

    • 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.
    • If the patient is unable to read any of the letters on the chart, the person checking vision should hold up fingers at varying distances and assess whether the patient can count them; this is recorded as counting fingers (CF) vision (e.g. CF at 4 feet, 1.2 m).

    • If the patient cannot count fingers, the person checking vision should move his/her hand across the patient’s field of vision to assess whether the patient can see this; this is recorded as hand motion (HM) vision.

    • Finally, if the patient is unable to see hand movements, a penlight should be swept across the patient’s eye to assess whether the patient can tell when the light is pointed at the eye. If they are able to identify when the light is pointed at the eye, this is recorded as light perception (LP) vision. If they are unable to identify the light, this is recorded as no light perception (NLP) vision.

    Provides a portable and quick method to assess visual acuity.

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    Result:

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    Next Steps
    Evidence
    Creator Insights
    Dr. Herman Snellen

    About the Creator

    Herman Snellen, MD, (d. 1908) was an ophthalmology professor at Utrecht University in the Netherlands. He was also the director of the Netherlands Hospital for Eye Patients. Dr. Snellen’s research interests included astigmatism, glaucoma, and correction of visual acuity using eyeglasses and ophthalmological surgery.

    Are you Dr. Herman Snellen? Send us a message to review your photo and bio, and find out how to submit Creator Insights!
    MDCalc loves calculator creators – researchers who, through intelligent and often complex methods, discover tools that describe scientific facts that can then be applied in practice. These are real scientific discoveries about the nature of the human body, which can be invaluable to physicians taking care of patients.
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