Re: [photo-3d] Stereo vision and eye spacing

["John A. Rupkalvis" <stereoscope@xxxxxxxxxxxxx>]

----- Original Message -----
From: "William Gartin" <william_gartin@mac.com>
To: <photo-3d@yahoogroups.com>
Sent: Sunday, March 11, 2001 11:03 PM
Subject: Re: [photo-3d] Stereo vision and eye spacing

> This reminds me of when I got my first pair of glasses as a kid
> (nearsighted). The ground seemed almost a foot farther away, though I've
> never really noticed as much difference with later prescriptions, so this
> could be partly due to a bad grind on the lenses.

Another possibility:  As most people get older, the most common the vision
shift is toward the presbyopic (farsighted).  In fact, the very word
"presbyopic" essentially means "older vision".

Lenses that correct for myopic vision (nearsighted) are negative lenses.
These do not magnify, they reduce.  Thus when you wear glasses that have
negative lenses, the images you see actually are smaller.

Then, as you grow older and become an adult, your vision will often
(probably usually, I don't have the statistics) become more presbyopic.
Most people that wear glasses as children find that when they become
teenagers and again when they become adults they will have changed
prescriptions at least twice.   This change is usually to weaker negative
lenses that will reduce the images even less (they will appear larger, that
is closer in size to the way they look without glasses).

If this progression continues, the person may be lucky enough to not need
glasses as an adult at all.   Until they get older still.  At some point
they may find that as they age they have to wear glasses again.  Only now
the vision will have progressed to the point where the prescription will
become totally presbyopic, and the same person who wore negative lenses as a
child will be wearing positive lenses in their golden years.  Then,
depending on the strength of the positive lenses, things will be magnified
(positive lens glasses are commonly known as "reading glasses").  Oh, well -
everything will appear to be larger than life.  An advantage.  I think.

JR


 

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