Try to close your eyes and walk around the room, not to say about using the computer. Almost impossible, yeah?
Human eye (source: Wikipedia)
Sensitive to wavelengths within the range of 380 (violet) to 780 nm (red), reacts to just a few fotons, this makes a human eye a great detector. Adding to this adaptation (ability to adjust the quantity of light falling on retina by changing the dimension of iris), accommodation (ability to adjust focus by changing the shape of lens) and 3D viewing (thanks to two eyes) – this is really complicated!
Have you ever thought about how does the eye evolved? There is a short story!