Amblyopia and Drivers Vision Test

I have amblyopia in my left eye.  Both if my daughters do, also.  When we take the DMV drivers vision test, we cannot see anything on the left side. It is just blank.  On a regular vision chart we can read down to the third or fourth line from the top with this eye.  And can see the remaining lines, just cannot read them.  I do not understand why this happens at the DMV, other than I know it has something to do with the machine we have to look into.  Could you please explain this?
PS Because of this happening at the DMV, they insist we are leagally blind in this eye (which isn't so) and have to have a restriction listed on our licenses. Thank You

[John C Hagan III, MD, FACS, FAAO]

Because you have amblyopia when both eyes are open your brain suppresses the central vision from the amblopic eye and only uses the peripheral vision. All your central vision comes from the good eye.

When you look through the machine it used polarizing lens to make a column of letters seen with each eye. Since both eyes are open the column in front of the lazy eye can't see.  

This is hope to "cheat" Read one set of letters then shut your good eye. Don't make this obvious, since the good eye is shut the brain will not suppress the lazy eye (it only does so under binocular conditions). You will then see the missing letters.

JCH III MD

PS Don't tell them who told you how to cheat.