I didn't start having my eyes checked until I was well into my 20s. It immediately occurred to me at my first exam: when they show you the same eye chart for your left and right eyes, immediately following one another, aren't you likely to cheat? You say it 2-3 times looking through one eye. If the second eye is worse, then you've already memorized the lower most line you can read and know the letters/numbers. Which means you will probably be able to 'read' them with the worse eye. You don't mean to cheat, but you just do.
I think they should switch charts for each eye. It would definitely be a better diagnoses when you don't know what you are expected to see.
Just a thought.