Re: Change in lens power with distance

On Wed, 20 Feb 2008 19:29:39 -0600, John O'Flaherty <quiasmox@xxxxxxxxx> wrote:

On Wed, 20 Feb 2008 13:51:31 -0600, Robert Martellaro
<robopt@xxxxxxxxxx> wrote:

On Wed, 20 Feb 2008 01:53:02 -0600, John O'Flaherty <quiasmox@xxxxxxxxx> wrote:

I wonder if someone could help me understand something about glasses.
I am 62, myopic, and don't think I have any accommodation to speak of.
My prescription is about -2,-2.25, averaging in the astigmatism.
When I got my eyes checked, I mentioned that I wanted a special pair
of glasses to watch TV, at a distance of 11 ft. (3.35 m),


because I found my old glasses blurry at that distance.

That's a common complaint when the Rx changes towards less minus or more plus.
Has it changed? Are your eyes healthy? Post the new unmodified (distance) Rx and
the lens powers of the old glasses.



I had (2004):
-2.5 -.5 90
-3.0 -.5 50

add +2.25

I now have (2008)
-1.75 -.5 90
-2.25 -.5 50

add +2.25

Ok, that explains why the TV is blurry with the old glasses.

It's changed a lot. It may be worth saying that the older
prescription was obtained by an automatic instrument, while the new
one was obtained by a phoropter and "is this better, or is this
better"? How much variation will there be between these two methods?

Autorefractors and retinoscopy are starting points, but the final Rx is
determined with lenses/phoropter.

I have had one pair of glasses made to the new script, and the
bifocals are almost unusable, because the lower segment has no
remaining correction at all, which may be ok for reading, but I don't
need glasses for reading.

They're not unusable, you just don't like them.

What I do need is some way to see the
speedometer of my car clearly, and to see items on grocery store
shelves or on a table in front of me without removing my glasses.

You and millions of other presbyopic ametropes.

I guess that's another matter, along with the fact that the bifocal line
lies almost within my level-headed field of vision.

Consider progressive power lenses. Bias the design for distance and
intermediate. Take them off to read for extended periods. You still may need
computer glasses.

Anyhow, referring to the original problem, the old glasses were ok
for driving, but not sharp and clear for watching TV,

They worked poorly for the TV distance because the Rx was outdated and
incorrect.

while the new
ones are good for watching TV but not sharp and clear for driving.

That's probably the doctors fault because the correct Rx would have made both
distances ok. However, I wasn't there, and you may have insisted that the doc
give you an Rx that was optimized for the TV distance.

I'd
like to order a new pair of bifocals that will be sharpest for
driving. At this point, I'm thinking of going with -2, -2.5 (restoring
one quarter diopter of convergence), with add of 1.5, which would make
the bifocal segment equal to my current computer glass prescription,
which is -.5, -1, and which works fine.

Look, you need to get good advice from both the doctor and optician. If you're
not comfortable with your present eye care providers then shop for new ones. It
may help if either the doctor or optician is about your age. Stick with the
independents, explain the circumstances and your concerns, and if you get blank
stares then move on.

Robert Martellaro
~~~~~~~~~~~~~~~~~~
Optician/Owner
Roberts Optical
Wauwatosa Wi.
~~~~~~~~~~~~~~~~~~
"Science is a way of trying not to fool yourself."
- Richard Feynman
.

Relevant Pages

  • Re: Does AR Coating Improve Vision?
    ... prescription and eyeglasses as soon as I could. ... these glasses is that the peripheral vision far surpasses the ... Not on the distance gaze, unless the distance Rx is very strong, over eight ... Regarding sharpness of the Ovation vs the Rodenstock, ...
    (sci.med.vision)
  • Re: Seeking re-assurance on my prescription
    ... further tests at both my usual distance for computer work and my preferred ... box on the prescription for "reading addition" for both eyes. ... getting headaches from my old glasses. ...
    (sci.med.vision)
  • Re: First progressives for computer user
    ... Sorry I forgot to say that the correction for the glasses that I have now ... -Without glasses the distance between my eye and computer screen where I can ... I don't know how to convert corrections from my prescription to distances as ...
    (sci.med.vision)
  • Re: deducing a reading/computer rx from a general rx
    ... does not know the distance to the computer. ... He could have asked for what purpose you wanted your prescription, a quite normal question for an optometrist and quite normal to prescribe according to these findings. ... Although an ophthalmologist should be capable in prescribing for glasses, it is my opinion an optometrist performs better in this field of eyecare. ...
    (sci.med.vision)
  • Re: Possible silly question about bi-focals
    ... Lots of variables, but one of the biggest is if you use a desk top computer with a high set monitor, you might be "craning" your head to get into the near part of a bifocal. ... Although it's a bit risky for me to guess at your age which can affect this a lot, you might start with a pair of single vision lenses that correct whatever distance you have the most problems with, and go from there, depending on how it works out for you. ... I actually regularly use 4 different glasses. ... The doctor suggested that because my work involves computers he would ...
    (sci.med.vision)