Definitions of Perfect Eye Sight
When buying glasses online, it is natural to wonder whether the end result will be perfect vision (or 20/20 vision. Just because the glasses are cheap (or inexpensive), does not mean that the optical quality and level of correction will be any less.
Usually the definition of perfect eyesight is termed as twenty twenty vision – but what does this actually mean?
If you believe that you have perfect or “20/20” vision when wearing your glasses, would this mean:
(a) Vision is accurate enough to pass a driving test i.e. you can see and decipher a standard number plate on a vehicle from twenty metres. (b) sufficient visual acuity to pass entry standards for careers such as a pilot or maybe even a snooker player. (c) been a couch potato too much and have absorbed too many Americanisms?
The correct conclusion is that all three of the above are accurate, and especially true for (c) as everyone except the USA use a definition of 6/6. Now the mathematically minded reader will immediately notice that the one standard is based on metric measurement and the other on imperial, 20 feet being Visiclear very very nearly the same as 6 metres. The standard of 6/6 relates to the “Snellen” Test Type, of which everybody, at some time, must have been asked to read the letters, whether in the course of a sight test or simply a routine medical examination. The design of the Snellen test type is based on the assumption that the normal eye can recognise or resolve details that subtend an angle of one minute; or 1.75 mm at 6 metres.
Now some readers will have been aware of this useful piece of information already and others may feel that could happily have passed through life without ever being made aware of it.
So why is that Britain, with its imperialist history has always used the metric system and the United States which once declined to remain a member of the British Empire has always used the imperial measurements.
Perhaps the USA could be persuaded to use 6/6 instead of 20/20. Would this make it eligible to apply to be reinstated as a member of the, somewhat reduced British Empire? Of course this may require some juggling of their standards and definitions – indeed it may even require a new act of congress to be passed so that the “new” country may fall back in line with the “old” country. Another way of looking at it however is that by this one small step, the modern Europe may bring the modern United States kicking and screaming into the twenty first century to use a metric system that has long been adopted as a worldwide standard and in then makes a lot more arithmetic sense.