People who lose vision in one eye because of an injury or a medical condition must adapt to a narrower field of vision and loss of depth perception. They still see small objects as well as before, assuming the other eye is normal.
People with strabismus (misalignment of the eye) or amblyopia (lazy eye) have poor depth perception because they have trouble using two eyes together, thus do poorly on tests of depth perception in an ophthalmologist’s office. In real-world circumstances however, they may function significantly better by benefitting from monocular clues such as shadowing and size comparison. Of course, this condition is best dealt with by early surgical correction.
At first, adults who lose vision in one eye tend to have a few fender-benders, and reach out next to the hand they want to shake. But with patience and time, they learn to use clues to depth perception that do not require both eyes.