Question

when we suddenly go out in the sun for the light in a room is switched on the eyes blink why

Answer 1

Because of Iris....
When we come back in a room from sun
Our iris is suddenly do not work
When our iris is adjusted
we can able to see.....

Answer 2

here is your answer:-
it happens because of when we enter a bright room then the size of pupil decreases so that small amount of light rays can enter eye. due to this sudden change in the size of pupil we are not able to see. moreover size of pupil can be controlled by iris. the colour of eye is colour
of iris.

hope it helped ^_^