How can I use the Snellen chart in my iPhone?
The Snellen chart for iPhone displays letters of reducing size. The distance and font size determine visual acuity. Place the iPhone at 13'8" or 4.2m (14 feet approx.) from your eyes, and cover one eye. Each eye will be tested separately. If you can read the first row of the Snellen chart then your vision is 20/20. Otherwise get closer at 9'1" (9 feet approx.) and try to read the first row again. If you can read now the letters then your vision is 20/40
How accurate is the Ishihara test from your website?
The Ishihara test for color blindness may be affected by the brightness (luminance) and color settings of your monitor. It can provide an approximate condition of your eyes response to colors, but to make it sure you should seek professional advice.