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Gary
medicine forum beginner
Joined: 18 Nov 2005
Posts: 21
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 Posted: Wed Jun 14, 2006 5:10 pm Post subject:
Toric lens and accomodation
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A quick query, anyone know if while wearing a toric lens, does it alter the
eyes accomodation abilities?
TIA
Gary |
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Neil Brooks
medicine forum Guru
Joined: 24 Mar 2005
Posts: 1148
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| Posted: Wed Jun 14, 2006 5:20 pm Post subject:
Re: Toric lens and accomodation
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On Wed, 14 Jun 2006 18:10:37 +0100, "Gary"
<gary@franklin49deletethisbit.freeserve.co.uk> wrote:
| Quote: | A quick query, anyone know if while wearing a toric lens, does it alter the
eyes accomodation abilities?
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I'm not an eye doctor, but ... I do wear toric lenses.
My first question would be "Why?" It seems like you're experiencing
something, and you're trying to understand what's causing it. If so,
perhaps you should elaborate.
What's the issue you're having?
What's your prescription?
What's your age?
These might lead you to a better answer....
Neil |
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tkopan1@yahoo.com
medicine forum beginner
Joined: 05 Apr 2006
Posts: 13
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| Posted: Wed Jun 14, 2006 5:48 pm Post subject:
Re: Toric lens and accomodation
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Yes, you will accomodate. If you are myopic and remove your glasses to
read, you are not accomodating fully. After Wearing a corrected
contact lens prescription, you should begin to accomodate normally
again. The same applies to lasik. If you are hyperopic (farsighted),
your are accomodating too much already. A corrected toric lens will
have you accomodate less.
-Dr. Tom
Gary wrote:
| Quote: | A quick query, anyone know if while wearing a toric lens, does it alter the
eyes accomodation abilities?
TIA
Gary |
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Gary
medicine forum beginner
Joined: 18 Nov 2005
Posts: 21
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| Posted: Wed Jun 14, 2006 6:07 pm Post subject:
Re: Toric lens and accomodation
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"Neil Brooks" <neil0502@yahoo.com> wrote in message
news:c9h0925f0rev1oq03a77vfvsbkefhl3gec@4ax.com...
| Quote: | My first question would be "Why?" It seems like you're experiencing
something, and you're trying to understand what's causing it. If so,
perhaps you should elaborate.
|
The reason I ask is that I'm presbyopic and my close focussing abilities
vary between wearing contact lenses and glasses. It's better with the
latter.
I've assumed this is purely because of the physical distance from the eye
when being corrected by glasses. Or does/can a toric contact lens constrict
the eye's accomodation abilities?
Regards
Gary |
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Neil Brooks
medicine forum Guru
Joined: 24 Mar 2005
Posts: 1148
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| Posted: Wed Jun 14, 2006 6:28 pm Post subject:
Re: Toric lens and accomodation
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On Wed, 14 Jun 2006 19:07:14 +0100, "Gary"
<gary@franklin49deletethisbit.freeserve.co.uk> wrote:
| Quote: |
"Neil Brooks" <neil0502@yahoo.com> wrote in message
news:c9h0925f0rev1oq03a77vfvsbkefhl3gec@4ax.com...
My first question would be "Why?" It seems like you're experiencing
something, and you're trying to understand what's causing it. If so,
perhaps you should elaborate.
The reason I ask is that I'm presbyopic and my close focussing abilities
vary between wearing contact lenses and glasses. It's better with the
latter.
|
Contact lenses REDUCE the amount of accommodation that a FARSIGHTED
person needs. They INCREASE the amount of accommodation that a
NEARSIGHTED person needs.
It *could* be just what you alluded to below (known as the "vertex
distance"). IF the vertex distance wasn't factored in appropriately
when either or both your glasses or contact lenses were made, then you
would effectively have different prescriptions.
If that's the case, you really *don't* have an apples-to-apples
comparison between specs and contacts.
You might want to get back with your optometrist to see if your
contacts need the prescription tweaked. Depending on your Rx, it
could be that you're due for reading glasses *over* the contacts.
Hopefully, one of the docs can sweep up behind me if need be ;-)
| Quote: | I've assumed this is purely because of the physical distance from the eye
when being corrected by glasses. Or does/can a toric contact lens constrict
the eye's accomodation abilities?
Regards
Gary
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Robert Martellaro
medicine forum Guru Wannabe
Joined: 03 May 2005
Posts: 187
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| Posted: Wed Jun 14, 2006 8:07 pm Post subject:
Re: Toric lens and accomodation
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On Wed, 14 Jun 2006 18:28:27 GMT, Neil Brooks <neil0502@yahoo.com> wrote:
| Quote: | Contact lenses REDUCE the amount of accommodation that a FARSIGHTED
person needs. They INCREASE the amount of accommodation that a
NEARSIGHTED person needs.
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....compared to eyeglass lenses. In addition, the prismatic effect (induced
base-in prism) with minus power lenses assists with convergence.
Regards,
Robert Martellaro
~~~~~~~~~~~~~~~~~~
Optician/Owner
Roberts Optical
~~~~~~~~~~~~~~~~~~
"If a million people believe a foolish thing, it is still a foolish thing."
- Anatole France |
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Philip D Izaac
medicine forum addict
Joined: 08 May 2005
Posts: 78
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| Posted: Thu Jun 15, 2006 8:26 am Post subject:
Re: Toric lens and accomodation
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"Neil Brooks" <neil0502@yahoo.com> wrote in message
news:k1l092te9oi1ks8j2og6a26nc07nnf661m@4ax.com...
| Quote: | On Wed, 14 Jun 2006 19:07:14 +0100, "Gary"
gary@franklin49deletethisbit.freeserve.co.uk> wrote:
"Neil Brooks" <neil0502@yahoo.com> wrote in message
news:c9h0925f0rev1oq03a77vfvsbkefhl3gec@4ax.com...
Contact lenses REDUCE the amount of accommodation that a FARSIGHTED
person needs. They INCREASE the amount of accommodation that a
NEARSIGHTED person needs.
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I thought it was the opposite, Highly myopic individuals need to accomodate
slightly more with their contact lenses and vice versa when presbyopic.
Base in prism when reading with spectacles also help.
Roland Izaac |
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JohnDoe
medicine forum Guru
Joined: 14 Jun 2005
Posts: 364
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| Posted: Thu Jun 15, 2006 10:21 am Post subject:
Re: Toric lens and accomodation
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Gary wrote:
| Quote: | A quick query, anyone know if while wearing a toric lens, does it alter the
eyes accomodation abilities?
TIA
Gary
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The short answer is "no". If you're experiencing difficulty with close
focussing while wearing a toric lens it could be due to the lens being a
slightly different strength to your glasses or various other factors. In
my opinion the difference in convergence required between specs and
contact lenses isn't really significant but I know that others disagree.
Dom |
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William Stacy
medicine forum Guru
Joined: 01 May 2005
Posts: 1177
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| Posted: Thu Jun 15, 2006 3:20 pm Post subject:
Re: Toric lens and accomodation
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Philip D Izaac wrote:
| Quote: | "Neil Brooks" <neil0502@yahoo.com> wrote in message
news:k1l092te9oi1ks8j2og6a26nc07nnf661m@4ax.com...
On Wed, 14 Jun 2006 19:07:14 +0100, "Gary"
gary@franklin49deletethisbit.freeserve.co.uk> wrote:
"Neil Brooks" <neil0502@yahoo.com> wrote in message
news:c9h0925f0rev1oq03a77vfvsbkefhl3gec@4ax.com...
Contact lenses REDUCE the amount of accommodation that a FARSIGHTED
person needs. They INCREASE the amount of accommodation that a
NEARSIGHTED person needs.
I thought it was the opposite, Highly myopic individuals need to accomodate
slightly more with their contact lenses and vice versa when presbyopic.
Base in prism when reading with spectacles also help.
Roland Izaac
I think you guys are comparing apples to oranges. |
Myopes have to accommodate more in full distance Rx glasses than they do
in full distance Rx contacts, although certainly less when not wearing
any correction.
Hyperopes have to accommodate less in their full distance Rx glasses
than they do in full distance Rx contacts, although certainly more when
not wearing any correction.
Now is that perfectly clear?
w.stacy, o.d. |
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Neil Brooks
medicine forum Guru
Joined: 24 Mar 2005
Posts: 1148
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| Posted: Thu Jun 15, 2006 4:04 pm Post subject:
Re: Toric lens and accomodation
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On Thu, 15 Jun 2006 15:20:43 GMT, William Stacy <wstacy@obase.net>
wrote:
| Quote: | Myopes have to accommodate more in full distance Rx glasses than they do
in full distance Rx contacts, although certainly less when not wearing
any correction.
Hyperopes have to accommodate less in their full distance Rx glasses
than they do in full distance Rx contacts, although certainly more when
not wearing any correction.
Now is that perfectly clear?
|
As mud ;-)
I can't find the two original cites that I used to post, but ...
here's a quote and the cite from which I pulled it:
"The accommodative demand on hyperopic patients is less with contact
lenses than with spectacle lenses, and so they are more readily
accepted"
FROM:
Fitting youngsters with contact lenses
From children to teenagers
http://www.optometry.co.uk/files/16b584a2c9ab1d496644a3d8e3b2184c_bansai20040924.pdf
OR: http://tinyurl.com/mxxsf
Interesting, and only tangentially related is:
http://aglasser.opt.uh.edu/publications/KV&G2003.pdf
I also found this:
"In this respect, it is interesting that wearers of glasses
accommodate less and have lower convergence demands than emmetropes or
wearers of contact lenses due to optical reasons" [presumably implying
the prism effect of the spectacle lenses, BUT ... CL's (primarily
RGP's) have this, too, no??]
FROM: http://www.agingeye.net/myopia/3.2.1.2.php
Which seems to cite this:
http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1175259&blobtype=pdf
OR: http://tinyurl.com/zj67f
Now THIS should clear it right up  |
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Robert Martellaro
medicine forum Guru Wannabe
Joined: 03 May 2005
Posts: 187
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| Posted: Thu Jun 15, 2006 7:33 pm Post subject:
Re: Toric lens and accomodation
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On Thu, 15 Jun 2006 16:04:50 GMT, Neil Brooks <neil0502@yahoo.com> wrote:
| Quote: | I also found this:
"In this respect, it is interesting that wearers of glasses
accommodate less and have lower convergence demands than emmetropes or
wearers of contact lenses due to optical reasons" [presumably implying
the prism effect of the spectacle lenses,
|
Hyperopes wearing glasses have the highest accommodative requirements,
emmetropes and contact wearers have lower accommodative requirements, and myopes
wearing glasses have the lowest accommodative requirements.
The prismatic effect is a separate issue from vergence considerations.
For example, look at three eyes, a -5.00DS myopic eye, an emmetropic eye, and a
+5.00DS hyperopic eye, all gazing at an object at a distance of one third of a
meter, with the spectacle plane (except for the emmetrope) 15mm from the eye.
Using U + D = V (for a thin lens system U is the vergence of the light
entering the system (U=1/u where u is the measure from the lens to the object.
D is the dioptric power of the lens and V=1/v is the vergence of the light in
image space as it leaves the lens) the -5.00D eye (vergence power entering the
spectacle lens = 3.15D, leaving the lens -8.15D, and at the cornea -7.25D),
(lens power -4.65 at the cornea), requires +2.60D of accommodation (-4.65 -
(-7.25) , the emmetropic eye +3.00D, and the +5.00D eye +3.50D of accommodation
(+5.40 - (+1.90).
Regards,
Robert Martellaro
~~~~~~~~~~~~~~~~~~
Optician/Owner
Roberts Optical
~~~~~~~~~~~~~~~~~~
"If a million people believe a foolish thing, it is still a foolish thing."
- Anatole France |
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Neil Brooks
medicine forum Guru
Joined: 24 Mar 2005
Posts: 1148
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| Posted: Thu Jun 15, 2006 7:46 pm Post subject:
Re: Toric lens and accomodation
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On Thu, 15 Jun 2006 14:33:51 -0500, Robert Martellaro
<robopt@nospam.com> wrote:
| Quote: | On Thu, 15 Jun 2006 16:04:50 GMT, Neil Brooks <neil0502@yahoo.com> wrote:
I also found this:
"In this respect, it is interesting that wearers of glasses
accommodate less and have lower convergence demands than emmetropes or
wearers of contact lenses due to optical reasons" [presumably implying
the prism effect of the spectacle lenses,
Hyperopes wearing glasses have the highest accommodative requirements,
emmetropes and contact wearers have lower accommodative requirements, and myopes
wearing glasses have the lowest accommodative requirements.
The prismatic effect is a separate issue from vergence considerations.
For example, look at three eyes, a -5.00DS myopic eye, an emmetropic eye, and a
+5.00DS hyperopic eye, all gazing at an object at a distance of one third of a
meter, with the spectacle plane (except for the emmetrope) 15mm from the eye.
Using U + D = V (for a thin lens system U is the vergence of the light
entering the system (U=1/u where u is the measure from the lens to the object.
D is the dioptric power of the lens and V=1/v is the vergence of the light in
image space as it leaves the lens) the -5.00D eye (vergence power entering the
spectacle lens = 3.15D, leaving the lens -8.15D, and at the cornea -7.25D),
(lens power -4.65 at the cornea), requires +2.60D of accommodation (-4.65 -
(-7.25) , the emmetropic eye +3.00D, and the +5.00D eye +3.50D of accommodation
(+5.40 - (+1.90).
|
I *think* I'm following you, Robert, and/but I'm very much intrigued.
When you speak of the vergence, or prismatic effect, even of a thin
lens, how is it calculated whether the prismatic effect is BI or BO?
Is it purely a function of whether the lens is minus or plus?? If so,
then is *that* the basis for the delta in accommodative demand
introduced by spectacles as different between myopes and hyperopes?
I'm curious because--if I DO understand you correctly, and--for
example--my spectacles (which do NOT have "added" prism correction)
INDUCE prism that is the *opposite* of what I need (inducing BO, for
example, when I'm exotropic), then I would need to force additional
accommodation simply to compensate for the inherent prismatic effect
of the thin lens, no?
Do I have that right?
If so, and if it is such a readily quantifiable issue, then
couldn't/shouldn't compensatory prism be introduced in spectacle
lenses--particularly higher power--to offset this effect and minimize
"spurious accommodative load?"
Thanks much, Robert. |
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Dick Adams
medicine forum Guru
Joined: 12 Oct 2005
Posts: 300
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| Posted: Thu Jun 15, 2006 7:50 pm Post subject:
Re: Toric lens and accomodation
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You're all nuts!
Any eye corrected to focus infinity unaccommodated will need to
accommodate 2 diopters to focus text at 0.5 meter, etc.
"Toric" does not change anything, except for being another one
of your misty concepts.
--
Dicky |
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Neil Brooks
medicine forum Guru
Joined: 24 Mar 2005
Posts: 1148
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| Posted: Thu Jun 15, 2006 7:58 pm Post subject:
Re: Toric lens and accomodation
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Dick Adams wrote:
| Quote: | You're all nuts!
Any eye corrected to focus infinity unaccommodated will need to
accommodate 2 diopters to focus text at 0.5 meter, etc.
"Toric" does not change anything, except for being another one
of your misty concepts.
|
The topic shifted. You simply didn't keep up.
The topic shifted into the relative accommodative demand induced by:
Glasses in hyperopes;
Glasses in myopes;
Contact lenses in hyperopes;
Contact lenses in myopes. |
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William Stacy
medicine forum Guru
Joined: 01 May 2005
Posts: 1177
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| Posted: Thu Jun 15, 2006 9:51 pm Post subject:
Re: Toric lens and accomodation
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Neil Brooks wrote:
| Quote: | When you speak of the vergence, or prismatic effect, even of a thin
lens, how is it calculated whether the prismatic effect is BI or BO?
|
I think Robert was using the term vergence to describe spherical
refractive power as opposed to prismatic effects. The term is confusing
because convergence can mean light focused by a plus lens, and it can
also mean turning the eyes inward (binocularly).
At any rate, you can tell if prismatic effect is base in or out by
looking at the profile of the lens. If it is a plus lens and you are
converging binocularly toward a near object, you are looking through
base out prism (the centers of your lenses are thick, the nasal edge is
thin, so your induced prism is base out). Just the opposite for minus.
Plano lenses have zero prism induced, no matter where you look.
| Quote: |
Is it purely a function of whether the lens is minus or plus?? If so,
then is *that* the basis for the delta in accommodative demand
introduced by spectacles as different between myopes and hyperopes?
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Nope. That effect is due to the differences in effective powers of plus
and minus lenses that are placed a finite distance from the eye, e.g.
spectacle lenses.
| Quote: | I'm curious because--if I DO understand you correctly, and--for
example--my spectacles (which do NOT have "added" prism correction)
INDUCE prism that is the *opposite* of what I need (inducing BO, for
example, when I'm exotropic), then I would need to force additional
accommodation simply to compensate for the inherent prismatic effect
of the thin lens, no?
|
If your lenses are plus, and you converge toward something near, you
indeed get a certain amount of base out prism. But if you added
compensatory prism for this, it would give you more base in prism in the
primary position, something you might or might not want.
| Quote: | couldn't/shouldn't compensatory prism be introduced in spectacle
lenses--particularly higher power--to offset this effect and minimize
"spurious accommodative load?"
|
If you are exo, you might indeed want some base in prism. The effect of
converging to a near object means that whatever base in prism you have,
it will be effectively less and less as you bring the object nearer and
nearer. Again, I don't think it has much to do with accommodation.
w.stacy, o.d. |
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