Now, having said that, it is possible to compensate for the loss of depth perception, which is probably what your friend is either consciously or, more likely, unconsciously doing. Engage in a simple experiment. Take two objects of equal size and, while your eyes are closed, have someone position one about a foot closer to you than the other. Now open one eye. You can tell which object is closer automatically not because you still have depth perception, but because the closer object is bigger than the further one. You know this instinctively. The brain itself can also make dramatic compensations for sensory losses, such as compensating for surprisingly large blind spots, which your friend may also be experiencing.