His difficulty can best be attributed to his lack of the depth cue known as "retinal disparity".
Retinal disparity is characterized as the manner in which that your left eye and your right eye see somewhat extraordinary pictures. The two marginally extraordinary pictures created in the two eyes are mixed into one view when the two eyes are open, and this is one of the manners by which human profundity observation is conceivable.
Retinal disparity is vital in checking how far away questions are. The more contrast (or more noteworthy uniqueness) between the picture each eye has of a similar question, the closer it is to you. The more distant away a protest is, then again, the more comparative it looks from review it with each eye alone.
