Double vision and Vision defect

Double vision noun - Visual impairment in which an object is seen as two objects.

Vision defect and double vision are semantically related. In some cases you can use "Vision defect" instead a noun phrase "Double vision".

Vision defect noun - Impairment of the sense of sight.

Double vision and vision defect are semantically related. Sometimes you can replace phrase "Double vision" with "Vision defect", this phrases are similar.