difficulty of making small corrections for distance vision

My vision has finally deteriorated to the point where I need glasses
for both near and distance. My problems are minor compared to those
of many people; yet the experience so far has been frustrating.

I got prescription glasses for distance. But distant objects (such as
birds) were still a bit blurry. After a month, I went back to my
regular doc (he'd been on vacation when I got the first exam). He
rechecked my eyes and found 1/4 diopter of astigmatism in one eye.

Things are slightly out of focus through my other eye, too, but I don't
know why.

He'll check my eyes one last time before I get the scrip filled. I'm
concerned we may miss something. He said my astigmatism was so minor
as to hardly exist, and, compared to the serious medical problems of
his other patients, I'm sure this is true. But *I* can sure see the
blurriness! It really takes the pleasure out of birdwatching, which
is my main recreation and stress relief.

Questions:

The "distance" part of the eye exam is done at only 20 feet. I'd think
that if you wanted your focus to be tack-on at 150 feet instead (given
that you can't have both), you'd test it with something further away.

Is there such a thing?

Also, the letters used for the exam are projected from an overhead
projector. They aren't that sharp to begin with. Most real objects
have a clearly defined edge, but these don't. Thus, it's hard to tell,
when looking through the exam machine, whether "this one or that one"
is better. But you sure can tell outdoors if something's not sharp.
Does anyone ever test distance vision using real objects - letters on a
sign, or something?

Also, it seems the test lenses do mostly gross corrections. If you
have only a little bit of astigmatism or prism or something, I'm
thinking maybe the examiners can't always find that, because their
tiniest correction is still way bigger than what you need.
True?

I'm pessimistic that we'll be able to correct everything that's wrong.
I'm also not sure how motivated the doc will be to fix the scrip from
"good enough" to "as good as possible".

What can I do at this upcoming exam to get the best results?

thanks...
LD
central USA

 

What does it involve? My curiosity is killing me now.

Is that a visible difference?
I'd rather the distant stuff be clear, at the expense of the closer
stuff.

I dunno how clear it's supposed to be. I got up on a chair and looked
at them on the wall. They have jagged edges up close; at a distance
these edges look soft or fuzzy. This is normal for an image projected
from a xeroxed transparency, but far from the crispness of a piece of
paper with letters printed on it.

(Please say more about that...)

Well.... I guess I'm skeptical because of my experience with it so far.
The first optometrist to examine my eyes (seen because my regular
doctor was out of town) did this test. When we got to that point, and
I said, "A is a little better than B, but both are still out of focus",
she said, "That's as good as it gets". I suggested there might be
astigmatism, and she put up a lens that when I looked through it made
things *totally* out of whack. So she said I didn't have astigmatism
at all. Since doc #2 says I do and she says I don't, this causes me to
think that maybe this test is not that precise. It might be the
person administering it, but I think the test images and/or test lenses
also make it harder for the patient to give reliable answers.

Yes, I get this impression too, that many people don't seem to notice
even rather large haloes, or misalignment, or whatever. Unfortunately,
I can indeed detect small differences in clarity. When birding, you're
often trying to spot something very small from quite some distance
away. Any deterioration of this capacity is noticeable, and
frustrating. (I'm probably spoiled, also, by having spent so many
years studying fine detail through very nice binoculars.)

Yeah, I don't know what 0.12 diopters would even look like. What IS
the smallest correction they have in that arsenal of test lenses,
anyway?

Can you say more about this? I thought that astigmatism was
manifested by thin lines looking double at one angle and OK at another
angle. So I would have tried to use E, M, and T. The Os are better?
What is "JCC"?

I'm afraid I'm going to go in there, do whatever can be done, and still
come out with glasses that leave much to be desired.

thanks,
LD
Indianapolis central USA
Home of the dull-colored warbler, the tiny cryptic sparrow, and many
birders with very expensive binoculars..... *sigh*

 

I sympathize with your desire to optimize your vision. You should
certainly shop around for an eye doctor who sympathizes as well. That
would be my first suggestion. My previous eye doc wanted to blow off
0.25 diopter of correction, which I found to make an absolutely
enormous difference. If you are like me, being 0.25 nearsighted
relative to what you are used to is totally unacceptable.

Having said that, I doubt going in increments smaller than 0.25 is
worth the trouble. Remember that your eyes can accomodate to near, so
you can overshoot the minus power by a smidge and you'll pull it in
when looking far away. Astigmatism doesn't work that way, but my
experience is that you simply can't notice errors smaller than 0.25.
And I've been called picky.

If you want to be anal and really understand what's going on (like me)
you can go out on E-bay and get yourself a cheap trial lens kit to
experiment with. I found it very educational, and you can hold lenses
up over your glasses or contacts to second guess your Rx in real life
situtations (like looking at birds?)

Have you considered RGP contacts? I recently changed, and the vision,
especially distance, is the best I've ever had. It took a few doctors
to get it right though, so I'd recommend seeking out someone who has a
fair number of RGP patients.

(I'm a patient, not a doctor)
--

 

I don't think that contacts are the answer for not being able to get a
proper script for spectacles. My experience is that approximately one
out of each three alleged refractometrists are able to get to within
0.5D of one's actual need for both of two eyes at one sitting. The
really bad ones may get bristly if challenged, like when you go back
with your new glasses and claim blur.

Yes, I agree that anality is the best answer here. I wish I knew more
about cheap trial lens kits. (I have got some, but they were not particularly
cheap). Having a test pattern for astigmatism on a wall can be useful also.
For me, the final test is reading lit signs at night, in the distance. In the
end, one must master the simple arithmetic of diopters which is sometimes
known to the phoropter jockeys (who, in my experience, are sometimes,
if not frequently, on-the-job-trained lackeys).

 

I have oblique axis astigmatism in both eyes, not much--.5 D I think,
but you're right--only the big "O" reveals it. I asked my optometrist
why doctors don't use the "fan spokes" image to test, and she said it's
old fashioned, not used anymore. Why is that? With the big "O" I have
to look at specific parts of it--the diagonal parts--and try to explain
which are blurry. My eye doctor had me turn the axis slider on the
phoropter (?) lenses to try to get the axis correct. This was minimally
effective.

I gave up getting the astigmatism correction in my glasses--there were
just too many variables--the Rx never seemed right. Partly it's the
type of lens, the shape of the frame, the accuracy of how the lens is
placed in the frame, the way the frame sits on my assymetrical nose and
ears...

And then my eyedoctor told me that the cylinder correction in the lens
only "corrects" about 15 degrees of arc, whereas, I perceive a greater
arc than that in my blurry astigmatism axis. Is this correct, or have I
misunderstood?

But viewing birds at a distance? For me, without binoculars--only
glasses, that would be impossible. And with my contacts, forget it.

Thanks,
C66

 

[Charles]
I sympathize with your desire to optimize your vision. You should
certainly shop around for an eye doctor who sympathizes as well.

[Mike Tyner]
I'd call a few offices and tell them you've had trouble getting a good
refraction, and ask which of their doctors have the best luck
satisfying engineers.

Ah HAH. Thanks for this tip.

[Dick Adams]
My experience is that approximately one out of each three alleged
refractometrists are able to get to within 0.5D of one's actual need
for both of two eyes at one sitting. The really bad ones may get
bristly if challenged, like when you go back with your new glasses and
claim blur.

Yes, that's what happened with the first one. :-(
I don't want to be a pain, but I would prefer to nail down the
refraction during the exam, even if that's tedious - rather than nail
it down by ordering glasses and looking through them. If the person
does a good exam, and finds that I have between zero and 1/8 diopter of
whatever, and there's no realistic way to correct for that, I'll live.
But I'd like to be confident that we did find out just what's wrong
with my vision. I'd like to not have to keep wondering whether if we
tried the exam yet AGAIN it would help.

The current person is an ophthalmologist, and he examined my eyes for
disease etc. as well. I think he is reasonably competent and patient,
but I worry that just by the nature of the test (especially those fuzzy
letters) and the natural flakiness of vision (it seems you need to look
back and forth at things a couple of times to be sure you're on
target), that it might take more than "reasonably". :-(


===============

[LD]

[Mike Tyner]
That's not typical. Mine are smooth, just a little blurring at the
limits of resolution for projection film.

Oh dear. I've never seen yours, so I can't tell if those I've seen
are any worse. Maybe they look find to most people and I'm just picky.
But the letters have never looked really sharp to me. They're dimly
lit, too. I feel as though my ability to accurately make fine
discriminations with them is limited. It's not like the close-up part
of the exam, where there is little doubt as to whether what you're
seeing is clear.

Why use a projector at all? Wouldn't it also work to just put a piece
of paper on the wall, in the same place, with the letters on it the
same size as they are projected on the wall? You'd see the same thing
in the mirror as you do now, and you could put a lot brighter light on
it too. Right?

I imagine the doc would have a cow if I brought such a thing in.

===================
[much info on how astigmatism tests work and what to look for]
Thank you all, this is very helpful. Phew.

[Mike Tyner]
The lens used to test astigmatism _should_ make things a little
blurry....

In other words, you make it too blurry - you overshoot - and then work
backwards to where it looks right?

Also:
My existing glasses correct for one eye being different from the other.

(Distance correct ion = +1.25 right eye, +1.75 left eye).
Will it help to wear these glasses before I go in? I'm thinking that
my eyes will have time to adjust to roughly where they need to be,
before trying to fine-tune the more difficult things.
?

===================
[various]
.....RGP contacts can be spectacular.

Thanks... I read about them (there is a good web site at

http://www.allaboutvision.com/contacts/rgps.htm

But my initial reaction is EEEEEEEEEEKKK you put something in your
EYE!!!!
Even seeing people wearing contacts gives me the crawls. The
description sounds like they might give really good vision, but I dunno
if I'm ready for them.

==================
[CC]
Viewing birds at a distance?

It's difficult. You have to locate the bird in the landscape first,
with just your glasses, before you can put binoculars on it. But the
birds try to stay invisible. Lately, I've been watching shorebirds,
because they tend to stand still out in the open, rather than rushing
behind a leaf. With birds in trees, you have to be fast, or all you
get is a glimpse of something's tail 2 seconds before it vanishes. I
can tell you of many fine tail views, or at least partial views, or at
least leaves that were almost partial views.....

cheers,
Liz D.

 

One of the problems with being an optometrist is that we do test in
unnatural surroundings. The peripheral vision is the major component in
focussing, but we block it out behind a refractor. We assume that 6m is
infinity, when it clearly isn't.

As a result, a percentage of people tend to get mildly overplussed,
resulting in fractional blur at distance. How do we eliminate this?
Longer rooms, trial frames, finishing off in the waiting room while you
look across the road, I am about to install a wall sized mirror to
reduce the effect of a wall 4m away.

I would recommend you get retested in a trial frame, then finish off
the final spherical component out of the consulting room.

dr grant

 

One of the problems with being an optometrist is that we do test in

(It is? I didn't know that.)

I've not heard of a trial frame, or of any testing being done outside
the exam room.
It sounds like a smart idea, but how would you get the exam lenses out
into the waiting room? (Remember, I don't know what most of this
stuff looks like.)
It does seem like it would be a bit more reliable to double-check the
scrip by looking at real objects that have real edges under good
outdoor light. I didn't realize you could do that without actually
having glasses made.

LD

 

CatmanX schreef:
We assume that 6m is

Add a - 1/8 dpt and you are done (I take it for granted you did know
already..)

A question related to this, do you use a red/green test?

Jan (normally Dutch spoken)

 

Adding -.125D can be misleadsing also. What we find in a refraction is
not necessarily what the eye wants in the real world. As much as most
(99%) of refractions are fine with what we find in the refractor head,
there is this small group that are probably active accommodators that
give funny results with their new specs.

And no, I don't use red/green, I can't do it (brain wiring probably)
and don't ask it of my ptients as I can't adequately explain what they
are supposed to get. I always finish with a frial frame and +/-0.25
flippers.

grant

 

(Sorry for posting to the group, but I can't get through to you via
private mail.)
thanks,
Liz D.