Puzzle From an Eye Corner

A little girl was sent to ana eye doctor after sustaining injury on her left eye following a blunt trauma from a fellow friend. The girl was complaining that the injuried eye was not seeing clearly.

An eye Doctor decided to examine both eyes thoroughly and finally he checked her vision, and he could not detect any deficient. He decided to do the visual field test by what they call confrontation test, where the girl had to fix her uncovered eye to the uncovered eye of the Doctor.

The eye doctor was puzzled to note that the girl was able to lacate and count accurately the fingers in all fields including the one an eye Doctor could not see!

The eye Doctor decided to put his fingers behind the girl's head, but yet the girl counted accurately the fingers!
The Doctor turned his head at his back to look for any puzzling event, but he just saw his usual wall at his back with nothing which can explain the girl's response, he then  pulled his chair and sat down with a deep a thoughts.

He eventually told the girl that her eye is okay, will recover from pain and she will be able to see clear in few days, but he finally asks her, how did she managed to see fingers behind her back?

What she answered... The Doctor was embarassed and admitted that he had learnt a lesson.

My readers, it is time for you to give your thoughts!!

Why do you think the Doctor turned his head and look behind his back wall when the girl was able to count fingers behind her back correctly?
Can you explain how did the girl managed to see the finger behind her back?
Can you guess the answer the girl gave to the Doctor?

I promise, if you get 50% or above from these questions, you are absolutely genius!!!