Put another way, suppose you have trouble seeing objects at a distance and you can only see out to 20 ft what a person with normal vision can see out to 200 feet, then you have 20/200 vision. The 6/6 terminology is more commonly used in Europe and Australia, and represents the distance in metres.
1 SID, also s.i.d., is a veterinary abbreviation meaning to give medication once a day. 2  Medical professionals for humans instead use the term qd (an abbreviation for quaque die). 3  However, that term can be easily mistaken with the term qid (an abbreviation for quarter in die), which means four times a day.
Medical Definition of q.i.d. (on prescription) q.i.d. (on prescription): Seen on a prescription, q.i.d. (or qid) means 4 times a day (from the Latin quater in die). The abbreviation q.i.d. is also sometimes written without a period in capital letters as QID.