Stereopsis tests your ability to fuse two similar objects in space. There are a number of tests for this. The fly/circles/animals test is probably most common. Worth 4 dot testing identifies suppression due to a central scotoma or diplopia. Testing fixation preference is a means of determining if amblyopia is present particularly in preverbal children and is not the same as ocular dominance. If a child does not alternate and hold fixation on cover/uncover testing we say he has a strong fixation preference with the assumption the non-fixating eye has amblyopia. People that are right or left eye dominant do not have any problems with depth perception or fusing unless they have some disruption of binocular fusion as a child.
As far as I know, there are no exercises or techniques to improve fusion, although patients often feel otherwise. Fusion/depth perception is a cortical phenomenon. Disruption of those pathways due to strabismus or amblyopia are not correctable beyond a critical period in early development. A better question is what degree of stereopsis is necessary to view depth at the slit lamp and using the indirect? My guess is gross stereopsis would be enough (i.e. fly), but this would not be optimal for discerning fine detail
