The ability to bring an object into sharp focus at close range varies based on the health of the neural retina, refractive errors, and interpupillary distance.

“Now, how close you can bring that object and still maintain it in sharp focus will vary from person to person based on a number of things. First of all, how healthy and well-performing their neural retina is, whether or not they have myopia or hyperopia, nearsightedness, et cetera, whether or not, for instance, you're like me and you have a fairly close inter pupillary distance, or whether or not you're more wall eyed and you have your eyes set further apart.”