The people who suffer from night blindness can't see things clearly at night. Maybe it is caused by lacking of vitamin A or pigmentary degeneration of retina. The patients need to have their eyes checked by an eye doctor immediately and apply for some appropriate treatment. The foods that are rich in vitamin A are good for their eyes.
If you can't see things clearly, you may get night blindness. It is a kind of eye problem. It can be caused by a few reasons so you'd better have you eyes checked by an eye doctor to see what caused your eye problem and then treat it timely. If it was caused by pigmentary degeneration of retina, you may need some medical treatment it immediately because it may lead to blindness.
The reason you don't see things clearly at night due to the photoreceptors in the retina of your eye.
You have two types of photoreceptors in your eyes - cones and rods. Cones allow us to see colors and work in bright lighting. Rods see black and white and work mostly in dim or dark lighting. SO, when you are in a completely dark room and you've become dark adapted, your cones are not being stimulated from bright lights and are not sending visual signals to your brain. Your rods take over and you can somewhat make out objects, shapes, and whatnot in VERY dim lighting.