https://www.ncbi.nlm.nih.gov/books/NBK558961/
Snellen Chart - StatPearls - NCBI Bookshelf
Invented in 1862 by a Dutch ophthalmologist named Herman Snellen, the Snellen chart remains the most widespread technique in clinical practice for measuring...
snellen chartncbibookshelf
https://play.google.com/store/apps/details?id=com.fonlow.snellen&hl=en_US
Snellen Chart - Apps on Google Play
Measure distant visual acuity
snellen charton googleappsplay