In article ,
Tim Lamb wrote:
You don't understand much about your own eyes, do you?

Well I've lived with them a long time so I Know them pretty well.

Apparently not.

:-)

From a point of technical ignorance, I'm with Bert.
Sat at the desk, I am wearing corrective reading glasses. Glancing
through the window, I can see trees on the horizon 1/2 mile away and all
the bits in between. However, nothing is in sharp focus.

Of course not. You've increased the power of your eye lens by using
reading specs, so they are no longer focused on the distance (infinity, in
practice)

The
registration on a van parked 20m away is blurred but just about legible.
If I take my glasses off, the computer screen is blurred but everything
else snaps into sharp focus.

Exactly what you'd expect with good vision as a youngster, as you age.

It remains my belief that adopting the bi-focals that Specsavers sold me
20 years ago would have caused endless dust/drizzle/condensation
nuisance during work related activities and might also have led to a
deterioration in distance vision.

Presumably those varifocals would have had no correction for distance at
all? So up to the individual if they would be more convenient than using a
reading etc aid as and when needed. And of course a shop will try and sell
you what gives them the maximum profit.

--
*Why is the word abbreviation so long? *

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