Disparate diopters...

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Frank M - 31 Dec 2004 05:29 GMT

I have a problem rx which has been corrected in the past but which I am
currently having problems
getting right. I sure would appreciate some direction as to how to
solve this problem, e.g. is it
in the prescription or the lenses or both - or other? (My MD otherwise
gives ok eye health.)

My left eye is -5.0 and right eye is -11.5 (w/o reference to the
spherical and axis). I've had this
corrected using base out prism...one O.D. prescribing 3.0 b/o and other
4.0 b/o, to correct a tendency
towards cross vision (in spectacles).

I can see out of either, but their sph and axis numbers vary - so
either pair causes pain after
a while. One rx is from a private O.D. who has tried a couple of
iterations, and the other is from
a lense crafters' O.D., and they've been through a couple of tries as
well. I've gotten distance and
near glasses from both places, and contacts from a previous O.D. ,
which get me very close to 20/20 but do not address the prism need, so
they are tiring as well.

Addressing the spectacles, where's the problem likely to lie - in the
rx or in the lenses, sic the materials and tolerances? Both places
seem to be "hurried" to get me in and out and both make
their own products. Would an independent Optician be more likely to
get the rx's translated
right, or try another O.D., or give up the ghost and go back to soft
contacts and get "over" glassess for the prism?

Thanks and regards in advance.

--
To email, change "nospam" to "fwmco"

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Dr. Leukoma - 31 Dec 2004 13:42 GMT

> I have a problem rx which has been corrected in the past but which I am
> currently having problems
[quoted text clipped - 31 lines]
> --
> To email, change "nospam" to "fwmco"

The problem likely lies with your vision and not with the eyeglasses. Are
you binocular, or do you see only out of one eye at a time (which would be
my guess)? What are your visual acuities with correction? Without knowing
anything else, I would guess that a combination of contact lenses and prism
glasses would have the best chance of working.

DrG

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Dom - 31 Dec 2004 13:54 GMT

> I have a problem rx which has been corrected in the past but which I am
> currently having problems
[quoted text clipped - 28 lines]
>
> Thanks and regards in advance.

Generally speaking I would rarely use base out prism, it can create more
problems than it solves. My first instinct (going only by the limited
information you have given) would be to try with no prism at all - how
do your eyes cope with that?

Questions for you to answer that will help me and other NG posters to
answer your queries:
What was the successful Rx that worked for you in the past (in
particular, how much prism worked for you in the past?)
What is the cyl & axis in your latest Rx (so as to compare with the
previous Rx which worked).
When do you experience the tired or pained eyes - when using the
distance or the near pair?
How do your eyes start to feel (e.g. 'tired', sleepy, dry, scratchy,
itchy; or more 'strained', achey, headachey, pulling, drawing)?
When do these symptoms start to appear (i.e. how long after starting the
task?)
What is your age?
Do you spend a lot of time reading or computing, or doing any other
particular task?

If you could provide answers to the above it would help 'us' to help
you... but my gut instinct is that the prescription, in particular the
prism, is the problem - rather than the manufacturing of said lenses.

To answer your other Q, in general I would say that a small independent
operation is more likely to really try hard to get it right than a big
corporate sausage factory. Of course, there are exceptions to every rule!

Regards

Dom

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Dan Abel - 31 Dec 2004 19:46 GMT

> My left eye is -5.0 and right eye is -11.5 (w/o reference to the
> spherical and axis). I've had this
> corrected using base out prism...one O.D. prescribing 3.0 b/o and other
> 4.0 b/o, to correct a tendency
> towards cross vision (in spectacles).

I'm a lay person, and don't understand this prism thing. As far as the
disparate diopters, I had that for five years, and contacts for distance
with reading glasses for close fixed that for that period of time.
There's no way to have binocular vision if you choose glasses for most
people with that much difference in the diopter correction.

Signature

Dan Abel
Sonoma State University
AIS
dabel@sonic.net

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Joe Stella - 31 Dec 2004 23:52 GMT

>> My left eye is -5.0 and right eye is -11.5 (w/o reference to the
>> spherical and axis). I've had this
[quoted text clipped - 7 lines]
>There's no way to have binocular vision if you choose glasses for most
>people with that much difference in the diopter correction.

Interesting. I'm a lay person too, and I don't understand the disparate
diopter problem. Assuming that each eye individually can be corrected
for clear distance vision (with the eyes having very different diopter
lenses) then why wouldn't there be adequate binocular distance vision
using both eyes at the same time? I can see where there would be a
problem at intermediate distances, where one eye loses focus before
the other one does, but why would distance be a problem?

Similarly, if both lenses were adjusted to bring reading distances into
focus, why is there a binocular problem when reading?

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Dr. Leukoma - 02 Jan 2005 00:04 GMT

>>> My left eye is -5.0 and right eye is -11.5 (w/o reference to the
>>> spherical and axis). I've had this
[quoted text clipped - 19 lines]
> Similarly, if both lenses were adjusted to bring reading distances
> into focus, why is there a binocular problem when reading?

Image size difference.

DrG

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Dan Abel - 03 Jan 2005 18:43 GMT

> >There's no way to have binocular vision if you choose glasses for most
> >people with that much difference in the diopter correction.

> Interesting. I'm a lay person too, and I don't understand the disparate
> diopter problem. Assuming that each eye individually can be corrected
> for clear distance vision (with the eyes having very different diopter
> lenses) then why wouldn't there be adequate binocular distance vision
> using both eyes at the same time?

I guess I should have explained that. The way binocular vision works is
that the two eyes send images to the brain, and the brain merges them
together into one image. Very strong minus lenses in glasses reduce the
image size, quite a lot. If both eyes need strong minus lenses, the brain
gets two small images, which then are merged. Since people who need
strong minus lenses can't see a thing without them (at distance), then
this doesn't matter. However, if one eye needs a strong minus and the
other doesn't, then the brain gets two images of greatly different sizes.
The brain cannot merge them, and the result is that the person sees
double. Eventually, some people can get used to this, and they don't see
double, but I don't believe that the brain is merging the images, it is
just blocking one of them, meaning that the person doesn't have binocular
vision.

Contact lenses don't reduce the size of the image (at least not nearly as
much). Thus, switching to contacts will get rid of the double vision
while enabling binocular vision.

I wore glasses for 35 years with strong minus lenses for both eyes. I was
then diagnosed with cataract, significant in one eye but very minor in the
other. As part of cataract surgery, the doctor normally replaces the
defective lens with a new plastic lens inside the eye. The patient gets
to choose the power. I chose to have my distance corrected, meaning I
wouldn't have to wear thick glasses anymore. However, the doctor advised
that after the first eye was done, but before the second eye was done, if
I chose to wear glasses, I would probably see double. He advised me to
switch to contacts, which I did.

Signature

Dan Abel
Sonoma State University
AIS
dabel@sonic.net

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Jkumar167 - 08 Jan 2005 21:44 GMT

>isparate
>diopter problem. Assuming that each eye individually can be corrected
>for clear distance vision (with the eyes having very different diopter
>lenses) then why wouldn't there be adequate binocular distance vision
>using both eyes at the same time? I can see where there would be a

It has to do with the magnification difference between the lenses. If you are
wearing spectacles, and have a five diopter difference between the two eyes,
one eye will see a LOT larger image than the other. This makes it difficult to
fuse the two images. The brain just won't do it. Frankly, I'm not sure where
prism will help either. prism might help hold the eyes straight (assuming one
tends to wander, which is often the case when there is a difference like this)
but it won't help with the fusion issue. You need fusion for true binocular
vision.

Contact lenses are often effective in these types of cases because they cause
less magnification differences when the power is disparate.

I hope this explains the issue in a way you can understand. I tried to avoid
jargon.

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