http://www.allaboutvision.com/eye-test/ Eye Test The Eye Chart and 20/20 Vision Eye Test Snellen’s tumbling E chart Eye Test - The Eye Chart and 20/20 Vision Explained Snellen’s tumbling E chart "The Eye Chart and 20/20 Vision" "The Eye Chart and 20/20 Vision" « The Eye Chart and 20/20 Vision » Snellen’s tumbling E chart Snellen’s tumbling E chart Snellen’s tumbling E chart