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Re: [OM] Dioptric Correction

Subject: Re: [OM] Dioptric Correction
From: Joe Gwinn <joegwinn@xxxxxxxxxxx>
Date: Sun, 14 Dec 2003 14:33:56 -0500
At 1:49 AM +0000 12/13/03, olympus-digest wrote:
>Date: Fri, 12 Dec 2003 12:35:18 -0500
>From: "Lama-Jim L'Hommedieu" <lamadoo@xxxxxxxx>
>Subject: Re: [OM] Dioptric Correction
>
>I told my optometrist I wanted to pay him for second examination, to come up 
>with the exact prescription needed for a distance of 1 meter.
>
>He said that with all of the technology available to him, he had no way to 
>test at one meter.  He could test at infinity and that's it.

Find a new optometrist.  Or better, an opthalmologist.  

I had no difficulty getting a prescription tuned to any desired distance.  
Specifically, I got one tuned to 18 inches (46 cm) for use with the computer 
and other close work, and my wife got one tuned to 24 inches (61 cm) for 
playing the piano.  We have different opthalmologists, and neither had the 
slightest difficulty.  They have a test fixture with a sliding holder for the 
eye chart.  They set the eye chart at the desired distance, and go to work.

The only problem I had was that the normal practice is to find the prescription 
for each eye independently of the other, and this almost always works OK, but 
failed for me (perhaps because my target distance was so close).  The problem 
was that the eyes fought with one another, trying to find a focus acceptable to 
both, but the two eyes were too far apart in implied target distance.   So, the 
opthalmologist did it over, this time doing a final adjustment with both eyes 
at once, and that worked.  I am wearing the glasses as I type these words.

The opthalmologists called these special prescriptions "computer glasses".

Aside from the obvious need to see despite aging eyes, I had another reason to 
want computer glasses -- safety.  When doing the close work, generally working 
on some kind of hardware, I found myself bringing my eye to within three or 
four inches of what I was working on, and worried that I would eventually poke 
myself in the eye with a sharp tool, or have something spring out and get me in 
the eye, etc.  The glasses both allow me to be farther away, and physically 
stop such things from getting to the eye.

In the US, opticians can only make glasses, optometrist can also fit glasses, 
but opthalmologists are licenced medical doctors and can everything, including 
eye surgery.


If you are older than 35, you should have an opthalmologist examine your eyes 
at least once every three years, need it or not, because some of the important 
eye diseases give the patient no warning symptoms before irreversible blindness 
sets in, but a doctor can pick these diseases up far before the patient can 
tell.  Optometrists won't do, it must be a opthalmologist.


>I decided to make the transition to AF immediately, before I'm too old to want 
>to learn something new.  Scary, but it's better than being dead already.

The opthalmologist plus new glasses is far cheaper, and doesn't force one to 
learn the ins and outs of a glass-equipped computer, a wunderbrick.  Nor is 
autofocus such a panacea.

Olympus should know the apparent distance they designed the viewfinders to.  
I've heard one meter and two meters, which are plausible, but don't know if 
either is correct.  One can test this by looking alternately through the 
viewfinder (at the split prism) and a wall, and move until switching between 
the two causes no shift in the eye's focus (which one can feel).


Joe Gwinn


>
>From: "Mike" <watershed@xxxxxxxxxxxxxxx>
> > I asked my optometrist for the correct prescription for this
> > distance. My old glasses would not work as
> > you suggest as they are for distance vision.


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