If you are thinking about ordering your glasses or spectacles online, then obviously a concern is whether they will match your glasses prescription and you will have good eyesight after receiving your glasses. Just because it is cheap to buy glasses online does not mean that they should not perfectly match your glasses prescription and your eyesight should be exactly corrected.If you were to say, as some people do, that you have twenty twenty vision with your new spectacles, would this mean that you have:

(a) Sufficiently good eyesight to meet the requirement of the Road Traffic Acts, i.e. you are able to read a number plate at a distance of 20 metres.
(b) Good enough vision to meet any required occupational standard such as that needed to become a Police Officer or an Airline Pilot.
(c) Been watching too much American television?

The answer is that with your new glasses you have all three of the above and in particular (c), because in all countries of the world, with the exception of the United States, the standard of perfect visual acuity is expressed as 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 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?

Better still, could all British citizens who at present say 20/20 be persuaded to say 6/6.

Tags: Buying Glasses Online, Glasses, Glasses Online, prescription spectacles, road traffic act, spectacles, twenty twenty

This entry was posted on Friday, February 27th, 2009 at 5:29 pm and is filed under Glasses. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.