Newly discovered medical reports about Hitler show that Hitler was, for
quite some time during WWI, "hysterically blind". I.e. he was
psychologically so devastated and scared of being sent to the front again
that he believed he couldn't "see" anymore.
Medical examinations proved that nothing was wrong with his eyes. The doctor
who treated him and similar cases, had used his own method of getting
through to hysterical patients like him: he started SCREAMING at them
(while they believed they were blind) and insulting them as cowards, giving
them orders to see and walk around by themselves, etc.
Actually that doctor's method was quite successful. It is believed that
Hitler's own SCREECHING during his speeches was derived from the
"SCREECHING method" performed by that doctor, while Hitler had no other
contact to the outside world except that doctor's voice.
That doctor, because he had written down a lot of embarrassing reports about
Hitler, after the Nazi came to power, at first was isolated and discredited
and later killed by the Nazis.
I saw it on a TV documentary a few weeks ago, don't know whether there are
already documents online.