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.
q means every (for example: qday = every day; q6h = every 6 hours). qid means 4 times a day. Other commonly used abbreviations include BID (twice a day) and TID (3 times a day). however qid is no longer a recommended way of giving orders because it is easily confused with similar abbreviations.