In article ,
R D S wrote:
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.

I'm not one of those who would need to drive to Barnard Castle to check my
eyesight. ;-)

I have a brick built block some way beyond the end of my garden, perhaps
30m away, and the pointing on the bricks gives a pretty good indication of
how sharp my distance vision is. Something I see each and every day when
sitting down having a coffee etc. With no correction, it could be a
concrete wall. ;-) With +2 ready mades, I see the vertical pointing but
not the horizontal. With prescription and astigmatism correction, all
comes good.

A couple of years ago, I went to Specsavers after being royally messed
about by my previous optician. That had taken over from my original one,
who was very good indeed.

I have gas permeable lenses for distance, and add specs for reading. My
local branch of Specsavers seemed to actually still do gas permeable
lenses at a reasonable price. I'd pretty well run out of decent spares -
all acratched. Not surprising given their age.

Decided to get some ordinary prescription specs for distance too - as an
alternative. Left the lenses out for 5 days before going for the test. The
specs I got have a bit too much 'plus' Pointing on that brickwork no
longer pin sharp. But easier to use the computer with.

Got them to prescribe some new hard lenses afterwards. About a quarter of
the price of the previous optician I'd left in a huff. And pretty good too.

--
*Be nice to your kids. They'll choose your nursing home.

Dave Plowman London SW
To e-mail, change noise into sound.