How to shift by using the eyechart to get most benefit?

[BrightStar]

I just wonder while I use the eyechart for practice shifting from one point of the letter to another and see the previous worse, will I have to see the letters best(most clear) or just as far as I could see the letters(most blur)? And which line on the Snellen eyechart should I use for the practice?

Thank you for your answer!

[David]

I don't understand what you're asking in your first question. As far as your second question, you can use any line on the eye chart where you can see the letters well enough to separate them. The lower the line, the better, because smaller letters have smaller details, and the letters a shorter distance apart.

Dave