I have strabismus (my eyes do not both look straight forward - one of them turns out when the other one looks forward) and anisometropia (my eyes have different prescriptions - my left eye is slightly farsighted, my right eye quite nearsighted).
Both of those conditions cause amblyopia*, because they cause the brain to receive different, incoherent signals from each eye. When this suddenly arises in adulthood, it causes diplopia (double-vision). When it arises in early childhood, since diplopia impedes sight, the brain learns to block out one of the signals.
In my case, the left eye is amblyopic. When I look at a scene, I see objects on the right and centre of my visual field with my right eye alone; only when I cannot see something with my right eye do I see it with my left. However, if I close my right eye, my left eye sees normally (though farsightedly).
If amblyopia is left untreated in childhood, it can go so far as to cause the recessive eye to be effectively blind; even though the eye itself is healthy, the brain does not use it.
Treatment, in my case, involved my wearing an eyepatch on the right eye for extended periods when I was little (say ages three to six or so). This allowed the brain to make the necessary connections to see out of my left eye, allowing me to retain sight in that eye, even though my right eye remains dominant.
As a result of my amblyopia, I do not have good depth perception; also I cannot see those stereogram things that were popular a while ago. I have investigated (partly for aesthetic reasons) a surgery to further correct my strabismus (when it emerged when I was 18 months old, it was partially corrected); I’m told this could cause my amblyopia to ease.
*Note. Further to what I said above, “lazy eye” is used for two different conditions, because they often occur together: strabismus, or deviated eyes, which is a physical condition in which the eyes do not point in the same direction; and amblyopia, a purely neurological condition.