> noticed for the first time something that is present in all
> eyeglasses,
> the images in the eyeglasses are smaller than the actual.

> 1. Is the reason the monitor look bigger without using
> glasses is because the image is defocused and hence
> bigger?

> If not, and reason being that the glasses are farther
> away, but if I put the glasses by pressing it to my eyes,
> I can still see the monitor as smaller. Why didn't it change
> bigger?

> 3. Can wearing contact lens give the same size
> perspective as actual for one to one size match?

> 4. How do you optimize your glasses to make the image
> you see as big as or close to the original.. such that
> seeing the monitor without glasses and putting the glasses
> slowly would make you see images size that are not far?

> 5. Does it have something to do with the power, meaning
> myopia with larger power (above -4.0D) would produce
> smaller image scale (or smaller monitor for example)?

> "Horus" <horus...[at]hotmail.com> wrote
> > But you said accomodation and convergence are wired together
> > and changing one can change the other.
> Clear vision is an equilibrium, a balance between convergence and
> accommodation. Equilibrium is a balance that can tip either way.
> > So if you reduce
> > convergence, you reduce accomodation.
> If you "assist" convergence, some people lose focus.
> > *But you said
> > that in eyestrain, one must reduce accomodation.
> No, I said most "eyestrain" is accommodative, not phoria-related. *IOW
> focusing (accommodative) problems are more common than convergence
> (diplopia) problems.
> Convergence is seldom treated with prism (by decentration or otherwise) when
> there is a normal phoria and no diplopia.
> > However
> > we can reduce convergence and hence reduce accomodation.
> That's right. Thing is, if you hold a book at 40 cm and _reduce_ your
> accommodation, THE PAGE GETS BLURRY.
> > Unless you mean there is a way to reduce accomodation
> > without reducing convergence? *How?
> Add +0.50 to your prescription. Most of us wouldn't adjust the PD when doing
> that.
> > Of course I have eyestrain daily when using computer 15 hours.
> > I just want to know ways to eliminate it by altering the glasses.
> Have your phoria tested. If it's normal, have glasses adjusted by +0.50 and
> quit worrying about prism.
> > It doesn't make sense to induce more base-in to converge less
> > by making the optical centers wider than the PD? I still
> > can't see the reason why it can't be done.
> Because near work gets blurry when you reduce accommodation. If you reduce
> the need for convergence, you usually must reduce the need for accommodation
> by incorporating plus lenses.
> OTOH converging assists accommodation, so if someone doesn't accommodate
> well, we might INCREASE the demand for convergence, to boost accommodation.
> > It's not commonly
> > done in the 1980s but with computers now becoming
> > part of our life and we using it 15 hours daily. We ought
> > to think of it.
> Not as you imagine.
> Until computers, 20 years ago the "nominal reading distance" for near vision
> was 16 inches. For grandma reading her Bible, that's about right.
> Now Gramma has a PC and a Wii and wants PC glasses that are clear at 24".
> > It's off by 0.5mm to 1mm. Is this allowance normal
> > in automatic eyeglass making machine or are certain
> > machines more accurate than others? In your machine,
> > can you produce 100% fully vertically centered OC,
> > that is, without *any 0.5mm-1mm off in the vertical
> > axis of the optical centers?
> Maybe things are different there, but I thought people made those
> placements, not machines. Anyhow...
> Test your phoria. If you don't have vertical phoria at the reading position
> in your glasses, the placement is fine. If you do have significant vertical
> phoria at your reading position, it'll get tiresome pretty quick and you'll
> want to ask for a remake. Wear them in, show the optician "things jump up
> and down" when you alternate your hand over one lens then the other.
> If the OCs are _perfect_ you can still always show vertical phoria in
> certain positions because your lenses aren't the same left and right. *Don't
> evaluate at the OCs. Evaluate your phoria at the position you read through.
> -MT

> "Horus" <horusocu[at]hotmail.com> wrote

> > It's not commonly
> > done in the 1980s but with computers now becoming
> > part of our life and we using it 15 hours daily. We ought
> > to think of it.
> Not as you imagine.
> Until computers, 20 years ago the "nominal reading distance" for near vision
> was 16 inches. For grandma reading her Bible, that's about right.

> Now Gramma has a PC and a Wii and wants PC glasses that are clear at 24".

> > It's off by 0.5mm to 1mm.

> But you said accomodation and convergence are wired together
> and changing one can change the other.

> So if you reduce
> convergence, you reduce accomodation.

> But you said
> that in eyestrain, one must reduce accomodation.

> However
> we can reduce convergence and hence reduce accomodation.

> Unless you mean there is a way to reduce accomodation
> without reducing convergence? How?

> Of course I have eyestrain daily when using computer 15 hours.
> I just want to know ways to eliminate it by altering the glasses.

> It doesn't make sense to induce more base-in to converge less
> by making the optical centers wider than the PD? I still
> can't see the reason why it can't be done.

> It's not commonly
> done in the 1980s but with computers now becoming
> part of our life and we using it 15 hours daily. We ought
> to think of it.

> It's off by 0.5mm to 1mm. Is this allowance normal
> in automatic eyeglass making machine or are certain
> machines more accurate than others? In your machine,
> can you produce 100% fully vertically centered OC,
> that is, without any 0.5mm-1mm off in the vertical
> axis of the optical centers?

> "Horus" <horus...[at]hotmail.com> wrote
> > I thought that there would be less chromatic aberration if I get
> > one made at 65.
> I don't see why.
> If you have color fringes around objects, that's chromatic aberration.
> If that's the problem you're likely wearing polycarbonate and your only
> solution is to get rid of the polycarbonate.
> Chromatic abb doesn't usually cause eyestrain.
> > So you are saying it's not much and impractical
> > to make one at 65 and you never made one for any of your
> > patient because there is absolutely no advantage of any kind?
> Probably not. Like I said, you probably wouldn't feel any difference.
> When eyestrain is a problem, we usually approach it by reducing
> _accommodation_, not convergence.

> > Know the relationship of convergence and power. Supposed
> > a patient had a myopia of only -1.5D at right side and
> > -8.0D at left side. Can the convergence change?
> A prism diopter or two. Prescriptions like that have other problems, and
> altering convergence doesn't fix it.
> > I use computer 15 hours a day. Convergence may cause
> > eyestrain so I thought if I can make the glasses wider
> > and induce more base-in for even more reduced
> > convergence demand, there would be less eyestrain.
> > Isn't this done in practice to get less eyestrain?
> Notice how you delicately skirt around the question - you only say that
> "convergence may cause eyestrain," not that you actually have it.

> In practice we usually adjust the spectacle power to help eyestrain. PD
> adjustments are a relative afterthought.
> > Convergence is normally inseparable from accommodation. If you
> > accommodate,
> > you converge. If you converge, you accommodate. If you alter one side of
> > that relationship without considering the other it's like running a
> > bicycle
> > with wheels of different sizes.
> > Why did you mention "convergence excess"? I mean, if I
> > make an extra pair of 65 oc (my pd is 68). The convergence
> > would be similar to people who don't use glasses, right?
> > Or are you saying that using glasses when reading
> > where the oc is 65 (looking directly at optical centers)
> > would produce more convergence than without using
> > glasses (supposed there were no myopia)?
> No, but it WOULD require more convergence if you happened to look across the
> room at TV, which you would inevitably do.
> > As I have said, just to get less eyestrain by reducing
> > convergence and accomodation when using monitor
> > 15 hours a day, nothing more. I have no abnormal
> > phoria.
> Typically we reduce "eyestrain" by reducing accommodation. Changing the
> phoria with induced prism is only likely to help if there is a phoria
> problem.
> Likewise changing the accommodation by changing the power is only likely to
> help if there's an accommodation problem.
> If we change one, we usually change the other because accommodation and
> convergence are wired together.
> Even so, accommodating and converging all day doesn't guarantee eyestrain..
> You haven't actually said you have eyestrain.
> -MT

> I thought that there would be less chromatic aberration if I get
> one made at 65.

> So you are saying it's not much and impractical
> to make one at 65 and you never made one for any of your
> patient because there is absolutely no advantage of any kind?

> Know the relationship of convergence and power. Supposed
> a patient had a myopia of only -1.5D at right side and
> -8.0D at left side. Can the convergence change?

> I use computer 15 hours a day. Convergence may cause
> eyestrain so I thought if I can make the glasses wider
> and induce more base-in for even more reduced
> convergence demand, there would be less eyestrain.
> Isn't this done in practice to get less eyestrain?

> Convergence is normally inseparable from accommodation. If you
> accommodate,
> you converge. If you converge, you accommodate. If you alter one side of
> that relationship without considering the other it's like running a
> bicycle
> with wheels of different sizes.

> Why did you mention "convergence excess"? I mean, if I
> make an extra pair of 65 oc (my pd is 68). The convergence
> would be similar to people who don't use glasses, right?
> Or are you saying that using glasses when reading
> where the oc is 65 (looking directly at optical centers)
> would produce more convergence than without using
> glasses (supposed there were no myopia)?

> As I have said, just to get less eyestrain by reducing
> convergence and accomodation when using monitor
> 15 hours a day, nothing more. I have no abnormal
> phoria.

> On Mar 19, 7:16*am, "Mike Tyner" <mty...[at]mindspring.com> wrote:

> My PD is 68 and if I get extra pair made at 65mm. It will be
> exclusively
> for near use and not far because I have the other glass made at 68.
> I thought that there would be less chromatic aberration if I get
> one made at 65. So you are saying it's not much and impractical
> to make one at 65 and you never made one for any of your
> patient because there is absolutely no advantage of any kind?
> > > My myopic power is -7.0D on right and -8.0D on left. Does the
> > > inbalance power mean the convergence on each eye is different?

> Know the relationship of convergence and power. Supposed
> a patient had a myopia of only -1.5D at right side and
> -8.0D at left side. Can the convergence change? In
> this case, how is the optical centers of the lens
> adjusted (if at all)? Just want a good theorerical
> grasp of relationship between convergence and power.

> In most cases, "reducing strain" indicates reducing accommodation.
> Accommodating stimulates convergence and it will still continue to do
> so if
> you make new glasses.

> > You seem to be saying that your vision would be better if you wore a few
> > p.d. of horizontal prism. *Why do you need to alter your vergence demand at
> > near?
> As I have said, just to get less eyestrain by reducing
> convergence and accomodation when using monitor
> 15 hours a day, nothing more. I have no abnormal
> phoria.

> > What are you trying to fix?

> Convergence is normally inseparable from accommodation. If you accommodate,
> you converge. If you converge, you accommodate. If you alter one side of
> that relationship without considering the other it's like running a bicycle
> with wheels of different sizes.

> "Horus" <horus...[at]hotmail.com> wrote
> > > I'm pretty sure you couldn't tell the difference.
> > Couldn't tell the difference of what? Couldn't tell or feel the
> > difference of the covergence assistance?
> Right. With glasses of ~-7.50, I doubt you could feel a difference between
> glasses made with PD of 68 and a pair made with 65. At least when reading,
> probably no difference.
> It's just as likely they'd be _uncomfortable_ for distance vision.
> > Remaking them with a PD of 65 would eliminate that assistance and require
> > you to converge _more._
> > But you said above I couldn't tell the difference. Or do you
> > mean other
> > thing beside convergence assitance, what is it that I couldn't
> > tell the difference?
> I mean that theoretically you will have to converge MORE with glasses made
> at 65 mm.
> You would also have to converge MORE if you glance up and watch TV far away.

> > My myopic power is -7.0D on right and -8.0D on left. Does the
> > inbalance power mean the convergence on each eye is different?
> For ease of calculation (induced prism, Prentiss' rule) you could assume
> both lenses are -7.50.
> > In such cases, what are usually done to the eyeglasses optical
> > centers? If my PD is 68. Should the glasses oc still be 68 or
> > should it be adjusted to compensate for mismatched power
> > of -7.0D and -8.0D?
> The PD should be 68.
> > You mentioned "Your glasses (pd 68) provide about 2.5 prism diopters
> > of "assistance" when you converge to a PD of 65".
> > How did you solve for the value of 2.5 prism diopters of "assistance".
> > How large should prism diopters be before one can significantly feel
> > the assistance?
> Prentiss' rule says diopters x decentration in cm = prism.
> 7.50 x 0.3 = 2.25 prism diopters.
> You could get fancy and figure each eye separately but you'll still round
> prism diopters to whole units, unless you want to give the lab guys a laugh.

> > If one's PD is 68 and one wants an extra pair for near view to
> > take advantage of the assistance. Does it make sense to make
> > the optical centers of the extra pair even wider than 68 to get
> > more base-in assistance or reduced convergence demand?
> Unless you have a complaint like headache or diplopia, you're obsessing.

> Convergence is normally inseparable from accommodation. *If you accommodate,
> you converge. If you converge, you accommodate. If you alter one side of
> that relationship without considering the other it's like running a bicycle
> with wheels of different sizes.

> Prism is prism, whether it's obtained by decentration or by actually
> altering the grind. Let's put Prentiss' rule aside.
> You seem to be saying that your vision would be better if you wore a few
> p.d. of horizontal prism. *Why do you need to alter your vergence demand at
> near?

> We'll want to know your phoria. What is your phoria at near?
> You can test it by looking at one single spot on a page, then watch the spot
> while you alternately cover each eye.
> Don't allow yourself to use both eyes during the test. Switch your occluder
> quickly, from one eye to the other, and measure the distance your two images
> "jump."
> That "jump" is your phoria, a resting position that depends on your anatomy
> and on your binocular reflexes. These reflexes have _learned_ to coordinate
> your accommodation and your convergence simultaneously, and somewhat
> inseparably.
> You can predict that people with _big_ phorias (jumps) will appreciate
> prism. To get a better prediction, you can test phoria at distance and near.
> But even with good, predictive formulas we don't go fixing stuff that ain't
> broke. Have any discomfort, double vision?
> What are you trying to fix?
> -MT

> > I'm pretty sure you couldn't tell the difference.

> Couldn't tell the difference of what? Couldn't tell or feel the
> difference of the covergence assistance?

> Remaking them with a PD of 65 would eliminate that assistance and require
> you to converge _more._

> But you said above I couldn't tell the difference. Or do you
> mean other
> thing beside convergence assitance, what is it that I couldn't
> tell the difference?

> My myopic power is -7.0D on right and -8.0D on left. Does the
> inbalance power mean the convergence on each eye is different?

> In such cases, what are usually done to the eyeglasses optical
> centers? If my PD is 68. Should the glasses oc still be 68 or
> should it be adjusted to compensate for mismatched power
> of -7.0D and -8.0D?

> You mentioned "Your glasses (pd 68) provide about 2.5 prism diopters
> of "assistance" when you converge to a PD of 65".

> How did you solve for the value of 2.5 prism diopters of "assistance".
> How large should prism diopters be before one can significantly feel
> the assistance?

> If one's PD is 68 and one wants an extra pair for near view to
> take advantage of the assistance. Does it make sense to make
> the optical centers of the extra pair even wider than 68 to get
> more base-in assistance or reduced convergence demand?