Why to Use
The Snellen chart provides a portable and quick method to assess visual acuity.
When to Use
Use the Snellen chart to assess binocular and monocular visual acuity in cooperative patients.
Next Steps
Edmund Tsui, MD
Priya Patel, MD
The Snellen chart provided in the MDCalc app is in-tended 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 supporting the use of smartphone applications (apps) for Snellen visual acuity is limited, and currently no app has been found to be accurate to within at least 1 line of formal visual acuity testing; further validation is required.
There are 2 main charts used to test visual acuity: (1) Snellen charts, which use a geometric scale, and (2) logMAR charts, which use a logarithmic scale. While both have been widely studied, Snellen charts are used more often in clinical practice and logMAR charts are used more often in the context of research studies, given the ease of statistical analysis. Data from 11 different smartphone apps found that the accuracy of the apps was limited; none were within 1 line of the true Snellen visual acuity (Perera 2015). One study suggested that the visual acuity on smartphone apps may not be completely accurate, but the results are reproducible, allowing the app to track change from baseline (Phung 2016). There has been 1 study validating the use of smartphone-based charts in measuring visual acuity; however, this validation was application specific and more studies must be conducted to evaluate the true validity of these charts (Bastawrous 2015).
Herman Snellen, MD
Original/Primary Reference
Validation References
Kelly O’Keefe, MD, FACEP; Sarah Temple, MD, FACEP
Ashley Norse, MD, FACEP; Jeremy Rose, MD, MPH, FRCPC
April 1, 2020
April 1, 2023   CME Information
4 AMA PRA Category 1 Credits™, 4 ACEP Category I Credits, 4 AAFP Prescribed Credits, 4 AOA Category 2-A or 2-B Credits
Price: $59
+4 Credits!
Kelly O’Keefe, MD, FACEP; Sarah Temple, MD, FACEP
Ashley Norse, MD, FACEP; Jeremy Rose, MD, MPH, FRCPC
April 1, 2020
April 1, 2023
4 AMA PRA Category 1 Credits™, 4 ACEP Category I Credits, 4 AAFP Prescribed Credits, 4 AOA Category 2-A or 2-B Credits
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