Re: New Rx

On Jul 26, 11:51 pm, "Ms.Brainy" <mikabra...@xxxxxxxxx> wrote:
On Jul 26, 4:46 pm, Dan Abel <da...@xxxxxxxxx> wrote:

If there was such a prescription, I would be interested
in 10/10 vision, 2/2 and 1/1 (all measured in feet). I believe that I
can get this acuity with my glasses. Am I mistaken?

I don't know what this means.

Why? What's so magical about 20 feet?

20 feet is termed optical infinity. anything beyond 20 feet will be
properly focused with the same lens power that provided clear vision
at 20 ft.

And 20/20 = 10/10 = 2/2 etc. They are all equivalent just like they
are equivalent mathematically.
these ratios simply mean-- what letter size you can read at X feet /
what letter size the population norm can read at X feet.



Most people's daily
activities, especially if they are of the presbyopic age, do not
require distance vision but rather intermediate and near. I found
long before my special eye problems began that my computer glasses
served me better around the house and for most of my indoors daily
activities. I switch to my distance glasses only for driving.
Wouldn't it make more sense to test and prescribe vision for 12, 10 or
5 feet instead of 20? Or in addition to 20? Does the formula for
"add" or "subtract" always work?

No. you measure the prescription at 20 feet which gives the lens
powers needed for the clearest possible distance vision (20 feet and
beyond = optical infinity). then to determine what is needed at any
distance closer than 20 feet is simply a calculation. Lens power (in
diopters) equals the 1/focal distance (in meters). Thus the lens
prescription to see an object at 12 feet (~ 4 meters) is the distance
prescription plus 1/4 diopters.

With progressive lenses like you are getting, what the optometrist
does is measure the distance prescription, then specify the add power
which is usually set on the high end, like +2.50 or +2.75 (that number
is dependent on age, whether cataract surgery has been performed,
working habits, etc.). The progressive portion of the lens will
therefore provide the proper lens power at all distances between
infinity and about 15 inches from your face depending upon how far
down in the lens you view the object (by holding it down or tilting
your head back). Determining the near add power is pretty simple for
progressives but more prone to error with lined bifocals since its
hard to know at what distance the patient does much of their near
work.


In any case, what counts is how well you
can see. I would suggest measuring the distance you read at, and the
distance from your eye to the computer screen, and give this information
to the OD next time you are checked.

I checked it with the following results, which I think are typical to
most people:

24" - 28" for computer
8' - 12' for TV viewing (in my case it's 10')
22" for relaxed reding
10" - 14" for reading & writing at the desk

All of these working distances can be easily achieved using a
progressive lens with a strong bifocal add. Your last measurement,
the reading and writing at a desk measurement, who cause me to want to
push your add power even higher to about +3.00D and even then you
would be more comfortable if you moved a little further back for
that-- say 13" - 16"


Moreover, the middle
portion of any tri-focals or progressives will be of limited height
(probably 10mm), which is practically almost useless. Why? I have
inquired about the possibility of having a larger middle section, and
was told that it does not exist, they don't make them this way. This
is very frustrating. The intermediate power is not even mentioned on
the prescription.

I am ready for a revolution!

Bull***-- many different progressive lens designs exist. Some are
optimized for larger reading and intermediate areas. Below is a link
to one such lens and I am not sure if it is even the best. A good
optician, such as Rob M who often posts in this NG, could tell you
many others and recommend the ones that are best.
http://www.zeiss.com/4125682000258738/EmbedTitelIntern/SOLAMAX_Sell_***/$File/SOLAMAX_Sell_***.pdf

BTW -- as your cat surgery was 4 weeks ago, then you should be healed
quite well and there shouldn't be further Rx changes to worry about.
Its time to go ahead with getting your new glasses.

Also, I would recommend getting a good anti-reflection coating on your
lenses with a no-stick teflon finish. Transitions would be a good add-
on if you are outside in direct sunlight a lot. They won't darken if
your are behind the windshield of a car however.


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