system
Given the following post, respond as if you're commenting on Reddit:
human
How does a lazy eye affect vision?

Can somebody with a severe lazy eye actually see out of that eye? Are they constantly looking in two places at once, or is it just the healthy eye that can see?

If they are looking in two places, how does that affect their visual field?
gpt
If you are referring to strabismus (as stuthulhu explained) combined with amblyopia, it directly impacts the perception of depth of field. Since the images from both eyes fuse thanks to the brain, and thus create "3D", the misalignment of one eye, and/or the fact that the brain takes only one eye into account upsets this balance. In Amblyopia, the subject would see perfectly fine, but miss the "third dimension", as in depth. 

There are a lot of variations within that. For example, if the person developed amblyopia in their first year, the brain effectively rewires itself to cope, and the person would have a sense of depth thanks to "motion parallax", or simply the motion of objects around him/her. (ex: "the ball gets bigger, so it must get closer") Another help in perceiving depth are shadows ("the darker the well, the deeper"), or simply the illusion of perspective ("the railroad tracks intersect far away") but all that is usually unconscious. As a matter of fact, a person may suffer from amblyopia and be completely oblivious to the fact that they lack the sense of depth. They may just feel they are "a little slow" in dodge-ball practice, or feel that cars are more unpredictable when they are driving. People who have lost an eye, or loose eyesight in one eye, or develop amblyopia later on are much more severely impaired as they may loose the complete field of vision for that eye, combined with the fact that they know what they are missing, and also the fact that the brain now needs to adapt to this new situation, which is uneasy.. 

Also, one can't assume that the amblyopic eye is "weaker" than the other, the brain, generally speaking, ignores the amblyopic eye, to concentrate on the signal sent by the other one. We are not quite sure why that is (is it that the eye is malformed? is it a "troubleshooting" problem in the neurons?). Generally, again, since the amblyopic eye hasn't had a lot of chance to "exercise", it tends to be weaker, but it may not have been the case at birth, or when the amblyopia was first detected. In some cases, the amblyopic eye is stronger than its counterpart, it simply remains latent, and can only work to its full extent when the other eye gets tired, or is covered up (which is why you may have seen amblyopic people wear patches, or use blurring drops). 

You also mentioned double vision, which can happen for various reasons: both eyes are taken into account by the brain but they are not aligned (this is not amblyopia generally, but "just" strabismus). An Amblyopic person can have double vision if their stronger eye gets weaker (when they are tired for example), in which case the other, amblyopic eye is "put on the line", therefore, the person will see double, but also may perceive both image with different strengths (one image clearer than the other). Double vision can also happen after an accident, if the brain has been affected and hasn't rewired properly. It is somewhat distressing to the person, and in most cases irreversible, but more people than you would suspect live with double vision. In fact, one can even have alternative vision (one eye for a while, then the other for a while)! In any case, it's never "lazy" :)

EDIT: added some clarifications, + some formatting.