focal plane problem

I hope that someone on this newsgroup might be able to suggest how to go
about solving a problem I have, that I am sure others must have as well.

My latest prescription gives me excellent vision in each eye separately, but
such horrible vision with both eyes open that I have abandoned my new
spectacles in favour of a pair from two prescriptions ago!

The problem is that the image in each of the two eyes is (it appears to me),
of different magnification, and in a different focal plane. I would much
prefer to have *less than perfect vision* in each eye, and trade off a
decrease in the focus and individual image quality against a *reasonable*
quality image that preserves stereopsis. I have heard several people of my
age complain of a similar problem, and several times the person has said
that their optometrist has acknowledged that there is likely to be an
"initial" problem, but apparently without proferring any solution other than
to "get used to the new prescription."

So what can/should one do? Is there any simple way of calculating a "good"
(not perfect) same-focal-plane prescription from my existing prescription?
At the very least (though not having an optometry background), I would have
thought that even a prescription based on the very old pair of spectacle I
now use, but with the astigmatic rotation updated, would be better than
either the old pair, or the new prescription.

If you have any suggestions, about (1) reading about the subject; (2) how to
approach the topic with an optometrist; or (3) how to do the calculations
.... I would be very grateful.

 

Yes if there is a big difference between the right and left lens power
that is causing you problems (known as anisometropia), it should be
possible to reduce the difference and improve the "balance" between your
eyes, probably at the expense of individual sharpness. However, this
would normally only be done once you have given the current arrangement
a fair go, say a few weeks of wear. What was your optometrist's advice?

Also you should have the optical centres of your lenses checked, just in
case they aren't aligned closely enough with your pupils (in the
horizontal and the vertical).

I should stress that you should take this advice with a grain of salt,
as I am only guessing at the problem based on your description.

Dom

 

Dear Mark,

The normal process of prescribing a lens is to ask you
"...is it better, is this better", and work to
clear each eye to pass the 20/20 line.

In general, the vision with the two eyes together is
generally better than each eye separately.

It is considered that this operation of the phoropter,
and "correct" lens places the focal plane of the
eye (and lens) on the surface of the retina -- for
each eye.

I do not know what the problem is, but by classical
definition, the focal plane of your eyes are
correctly "set" by that external lens.

Since you see well with the older pair of glasses,
I would go bact the OD and discuss the specific
issue you described to us. He will be responsive
and will perhaps use a different prescription
process.

Please let us know what he says.

Best,

Otis
(I am not an OD)

______

 

Perhaps you could post your prescription, that would help us. I was
diagnosed with cataract some years back. We discussed what strength of
lens I wanted implanted. The doctor warned that I would probably not be
able to wear glasses after the first surgery, since the prescription in
the eyes would be so different that the brain wouldn't be able to merge
the two images, due to the difference in magnification. He suggested
switching to contacts, which I did, at age 45. After the first surgery, I
got some glasses, mostly to see what happened. I sat in front of the
house, after taking out my contacts and putting on my new glasses. I
watched the cars go by. They were in pairs, one on the ground and the
other about ten feet in the air!

I would give your new glasses a couple of weeks, to see if your brain
could merge the two images. If not, take them back and explain that they
just don't work. The OD can verify if they were made correctly, and then
advise you what to do to get glasses that work for you. He can adjust the
prescription so they more closely match. Of course, if your problem is a
difference in prescription between the two eyes, contacts will solve the
problem. This is what I did for the five years between my two cataract
surgeries. Now that I've had both done, I can go back to wearing glasses.

 

Thanks to all three who replied.In reponse to the various questions that
were raised, I wore the new prescription spectacles for a couple of months
before reverting to the very much older pair, and in that time I never
seemed to get either good stereopsis or a general sense of good vision,
notwithstanding that the vision in each eye individually was very good.

The prescription, given that you asked, is

Right Sphere = +0.50 , Cyl = -1.50 axis = 18.0
Left Sphere = +1.25 , Cyl = -1.50 axis = 175

I shall go back and talk to the optometrist as you suggested, but if, given
the extra information, you have anything to add, I would be glad to hear.

Cheers,
mark

 

Yes, the .75 difference in your sphere would not cause the problems I was
referring to in another post. I believe that I was told that a difference
of 2 or greater was needed to prevent the brain from merging the images.
I had a difference of 10! Hopefully the OD can fix you up.