On 02/02/2021 10:52, Dave Plowman (News) wrote:
In article ,
charles wrote:
In article , Brian Gaff \(Sofa\)
wrote:
Yes well, I'd be too. Back when I was a child some home or other remote
venues were used for eye tests, if the room dimensions were too small, a
mirror was used and a mirror image letter chart was hung behind the
patient so they could see it in the mirror. It worked well. Brian

That technique is still used in 'proper' venues. Certainly in my local
Specsavers.

Anyone have the figure for the minimum distance between eye and chart
(using mirrors when needed) to give 'infinity' for practical purposes?
I've a feeling not all setups have enough lenght.


Historically testing distance was 20 feet hence the term 20/20 (a letter
that subtends summat degrees of arc....or summat....at 20 feet) or
nowadays 6/6 in metres. So usually 3m and a mirror.

Presumably test charts had the letters made a standard size designed to
work as above but nowadays you can have a screen displaying different
sized letters calibrated to the testing distance.

I don't know if there's a stated minimum but there comes a point where a
shorter testing distance can be problematic in gaining an accurate Rx.

It's all about cramming them them in and making them look modern though
these days.