# Optical Forums > Ophthalmic Optics >  Poly and acuity loss?

## eye1u2see2020

Hi all, I have a quick question or verification.  The lead lab tech had told me that people will lose 2 lines of acuity by just using poly.  Is there any information out there that will show that this is not correct.  I have worked in this field for 15 years and have never heard this.  I know that there is a higher abberation value and that poly is not the best optically, however I don't think that you lose 2 lines of acuity.  Please help me to disprove this theory.
Thank you
Rick

----------


## Judy Canty

I've been wearing poly for YEARS with no loss of acuity.

----------


## hcjilson

I have 2 pr of identical Rx's in Definity, both in the same 3pc mounting. One is in poly and one trivex. I went to poly for the transitions which is not yet available in Trivex Definity's. (2nd quarter and still counting!) They are both excellent but the fact of the matter is that my Trivex's are "clearer" My Rx is 5 and just over +5 in the distance with marginal astigmatic correction, and a 3 add. In terms of acuity I don't think I drop a line with poly but things seem a lot sharper with Trivex. It's nothing I can verbalize which is why I hesitated to bring it up, but my vision is better through Trivex. I also own a pair of 1.67's and same thing applies. My Trivex is clearer.

Pete and I have been going around the Trivex vs poly circle for years and he may be tempted to say that I've just bought the hype, but I KNOW how I see and it has nothing whatever to do with hype. Acuity loss?? I don't think so or marginal at best. I really don't know what to make of it!

----------


## chip anderson

Some folks think there is a lot of loss with Poly, some folks can't tell the difference, some think they are the same.
Same with AR some folks think it's wonderfully better, most folks can't tell the difference (at least from the patient's side of the lenses.)
But I can absolutely find you any number of opticians and quite a few patients that will swear that their being able to "prove" any of the above statements is true.

Chip

----------


## hcjilson

I can sure tell the difference driving at night, between AR and non AR. Of course, Chip hasn't experienced that yet because he is much younger than I, and his cataracts haven't developed yet!!!  :):):):)

----------


## MarcE

Your lab tech is full of crap.
However, when you look off center in a low abbe material (poly), there is distortion.  This distortion is proportional to the Rx power, and proportional to the distance off center. This distortion is not obvious at all to most of the population.  The higher the Rx, the more noticable the distortion.  I see hyperopes notice this more than myopes because the add power increases the absolute power of the Rx.

From the previous post, HC's total near power is over +8.0, and when reading he is looking off center by at least 16mm.  That is why he notices that Trivex is clearer.

You can see this in a lensometer.  When checking the add in a high hyperope in poly or 1.67 I notice that even when I get the mires as clear as they can be, they still aren't exactly clear.

In another thread, drK reported that 80% of the Rxs are between +/- 3.00.  So poly should not be a problem for 80% of the population.

----------


## Happylady

> Your lab tech is full of crap.


I agree!

Two lines? What a ridiculous thing to say. I can see the 20/15 line on the eye chart. So if I look at it with glasses made with polycarb I should only be able to see the 20/25 line if he is right. 

It is easy to prove him wrong. Look at the eye chart through a standard cr39 lens and then look at it through a poly lens.

I honestly can't tell the difference when I look through poly, 1.6, 1.67, or regular plastic. I have glasses in both poly, 1.6, and cr39 right now and I see no difference. I know that is not true for everyone, though.

----------


## HarryChiling

Yes at a certain Rx a patient will lose visual acuity, if we were to look at a line on the chart generally a 0.25D change will equate to one line on the chart. We know that poly has an n=1.589 and an abbe=30 so lets break it down:

*abbe = (nyellow-1)/(nblue-nred)*

so pluggin in our givens:

*30 = 0.589 / (nblue-nred)*
*(nblue-nred) = 0.589 / 30*
*(nblue-nred) = 0.01963*

Now we can make a fairly accurate assumption that the wavelengths for the red and the blue fall equadistance from the yellow wavelength except on opposit sides of the spectrum so then we can make the assumption that the indices are also equadistant from the yellow index. So lets put that word problem into a formula so that we can reduce the above even further (I used the average but it may be more accurate to use the mean instead, I don't know how much accuracy would be lost but you could always tweak the formula around here to see what the outcome would be):

*nyellow = (nblue+nred) / 2*

Now if we were to solve the above equation for both red and blue:

*nblue = 2*nyellow - nred*

and

*nred = 2*nyellow - nblue*

Now we can use these formulas in the top equation to further reduce to get our indices for red and blue:

*2*nyellow - nred - nred) = 0.01963*
*2*nyellow - 2*nred = 0.01963*
*nyellow - nred = 0.01963 / 2*
*1.589 - nred = 0.009817*
*nred = 1.579*

Now to solve for our blue index:

*nblue - (2*nyellow - nblue)= 0.01963*
*nblue - 2*nyellow + nblue= 0.01963*
*2*nblue - 2*nyellow = 0.01963*
*nblue - nyellow = 0.01963 / 2*
*nblue - 1.589 = 0.009816*
*nblue = 1.599*

Now we know our blue and our red indices in the poly medium and we know we don't want a greater than 0.25D of difference between the two in a lens. So let's set that up as an equation:

*Dblue - Dred = 0.25*

Alright now we need to break that down even further into a radius of measure if we are to get a constant:

*[(nblue - 1) / radius] - [(nred - 1) / radius] = 0.25*
*(nblue - 1) - (nred - 1) = 0.25 * radius*

Subbing out our known values:

*(1.599 - 1) - (1.579 - 1) = 0.25 * radius*
*0.599 - 0.579 = 0.25 * radius*
*radius = 0.02 / 0.25*
*radius = 0.08m*

So now we need to know what power so we are going to use our reference wavelength in our radius to diopter equation:

*D = (1.589 - 1) / 0.08*
*D = 7.36*

So now you know that to get a 0.25D difference or the equivalent of one line of visual acuity loss the power of the lens would need to be 7.36D, of course prism is another question all together and would require a whole nother post. ;)

----------


## drk

> Yes at a certain Rx a patient will lose visual acuity, if we were to look at a line on the chart generally a 0.25D change will equate to one line on the chart. We know that poly has an n=1.589 and an abbe=30 so lets break it down:
> 
> *abbe = (nyellow-1)/(nblue-nred)*
> 
> so pluggin in our givens:
> 
> *30 = 0.589 / (nblue-nred)*
> *(nblue-nred) = 0.589 / 30*
> *(nblue-nred) = 0.01963*
> ...


One of your assumptions is incorrect...one quarter diopter does not equal one line of visual acuity.

It's more like 0.50-0.75.

So, in the Chilinguerian fashion, add fudge factor 0.62 / 0.25 = 2.5
2.5 x 7.36D = 18D

As you can see, the conclusion is practically the same: it's a non-issue.

P.S. I enjoyed your color-coding. I think your method for determining dioptric difference between long and short wavelengths was quite nice. I think, though, that there was a methodology flaw...

When refracting with a glass lens and a monochromatic chart, the "correct" or "reference" refractive correction is arrived at, we agree to assume.

If the lens is fabricated in that power, the "dioptric dispersion" you calculated above will occur at black-white interfaces and "veil" the edges with chromaticity, which can perceivably affect acuity (although it is not completely safe to assume...).

But with a spread between red and blue of even 1/2 diopter, the observer would only see one half of that interval...with a white-on-black edge there would be only the red fringe visible (but not the blue, which would occur looking through the lens on the opposite side of the optical center). 



So, to summarize the fudge factors, you'd have to further double even what you did above, making it ~28D!

----------


## HarryChiling

> One of your assumptions is incorrect...one quarter diopter does not equal one line of visual acuity.
> 
> It's more like 0.50-0.75.
> 
> So, in the Chilinguerian fashion, add fudge factor 0.62 / 0.25 = 2.5
> 2.5 x 7.36D = 18D
> 
> As you can see, the conclusion is practically the same: it's a non-issue.


Thanks for the catch and yes it does change things in the above equation but the fact still remains that there will be a differnce of 0.25 between the red and blue wavelengths or across the visible spectrum in a 7.00 lens. If we were to look at the TCA in the same lens:

*TCA = 7.36 / 30*
*TCA = 0.25*

In Mohamed Jalies book he refers to a TCA of 0.10 as being significant and as you could see this power has 2 1/2 times that amount of aberration. I have been over this before but a lens power with TCA of 0.10 in poly would be:

*Power = 0.10 * 30*
*Power = 3.00D*

It's not to say it's gonna effect everyone but powers above a 3.00 could potentially affect some, just to add a side note.  I wear a -5.00 in a poly and it has never bothered me, matter of fact if I look I can see color finges when I look at edges of contrasting colors like black/white.  It has never bothered me and I also would point out that in certain powers a degree of TCA will be present no matter what, so there is probably nothign that can be done in some cases but the moderate to high range shoudl have an appropriate material.  I have drunken from the Fezz juice lately and have been dabling in the Trivex and must say I am impressed so far and the price seems more reasonable lately so I think it is something that should be a great tool in situations like this.

----------


## dbracer

These posts are excellent. 

It's been awhile since I given thought to such matters and you've made me delve into the literature and refresh myself on these matters. 

To the original question the answer is short. Poly has poorer optics. Whether it bothers depends on the SRx and the patient, but it's seldom 2 lines of VA - not that it couldn't be in specific situation.

The various Trivex's are good, but the index separates them from "hi-index" lenses.

Once again drk and Harry, dang good posts.

Respectfully,
dbracer

----------


## HarryChiling

Thanks for the data Darryl always precise and on time, not bad on the estimate though I was off by 0.001 from your estimate.  I love it when I throw a dart and it lands close.:bbg:

Now TCA and LCA would they have the same effects on VA?  If so then the TCA computed in the above would be equivalent to a VA of 20/28, right?

----------


## Darryl Meister

> The lead lab tech had told me that people will lose 2 lines of acuity by just using poly.


I actually have a table of visual acuity values as a function of lateral chromatic available online at Chromatic Aberration Course. This table is based on a study done by Meslin & Obrecht, "Effect of Chromatic Dispersion of a Lens on Visual Acuity."

And you can calculate lateral chromatic aberration (C) by dividing the prism (P) produced at a given point through the lens (using good ole' Prentice's rule) by the Abbe value (v) of the lens material:



So, at 10 mm (1.0 cm) from the optical center, a +5.00 D polycarbonate lens, with an Abbe value of 30, will produce the following lateral chromatic aberration:





which corresponds to a visual acuity of roughly 20/25 in Meslin and Obrecht's study...




> Thanks for the data Darryl always precise and on time, not bad on the estimate though I was off by 0.001 from your estimate. I love it when I throw a dart and it lands close.


Very true. ;)

The differences would become more significant as you approach the far ends of the spectrum, particularly in the blue end. Across the central wavelengths, the refractive index varies nearly linearly and, for most ophthalmic lens materials at least, the difference between the refractive index of the blue hydrogen line and the red hydrogen line is relatively small.




> Now TCA and LCA would they have the same effects on VA? If so then the TCA computed in the above would be equivalent to a VA of 20/28, right


Lateral chromatic aberration is generally considered much more problematic. Keep in mind that the eye actually suffers from roughly 1 diopter of axial or longitudinal chromatic aberration. Also, since axial chromatic aberration may play a role in the accommodative mechanism, the visual system probably chooses the best color focus for a given object.

----------


## dbracer

> As it turns out, the refractive index in the blue end of the spectrum changes more rapidly than the refractive index in the red end...


Now we're getting ridiculous. 

When the formulas start looking like hieroglyphics and the one-up-manship looks like the last round of the Olympic tryouts, it's time to look at your motives. 

Enough is enough, and it can be said a lot simpler. 

Respectfully,
dbracer

----------


## Darryl Meister

> When the formulas start looking like hieroglyphics and the one-up-manship looks like the last round of the Olympic tryouts, it's time to look at your motives


I was sharing information that I found to be very interesting, myself, including the results of a clinical study that speaks directly to the problem. Although I've been sharing this kind of information with fellow OptiBoarders for over 13 years now, I do understand that not everyone shares a passion for the "details" or more pedantic side of this stuff. As for the formula, I have no doubt that it did not look like hieroglyphics to Harry, who may very well find a generalized equation for refractive index useful for a number of applications; I actually developed it for a computer program that must convert between helium d and mercury e refractive index values for power calculations in different countries.

----------


## HarryChiling

> I was sharing information that I found to be very interesting, myself, including the results of a clinical study that speaks directly to the problem. Although I've been sharing this kind of information with fellow OptiBoarders for over 13 years now, I do understand that not everyone shares a passion for the "details" or more pedantic side of this stuff. As for the formula, I have no doubt that it did not look like hieroglyphics to Harry, who may very well find a generalized equation for refractive index useful for a number of applications; I actually developed it for a computer program that must convert between helium d and mercury e refractive index values for power calculations in different countries.


You know I definately appreciated that, I was almost positive that the relationship wasn't linear and for an example here I figured a estimation would suffice, but like you I program and when the computer is doing the heavy lifting you tend to throw big weight at it.

----------


## Darryl Meister

> You know I definately appreciated that, I was almost positive that the relationship wasn't linear


Oddly enough, I searched through a dozen different optical engineering textbooks and countless websites when I was trying to find a reasonably accurate dispersion equation for calculating the refractive index of a lens material at an arbitrary wavelength, and I couldn't find one single example that relied only on the Abbe value and mean refractive index. So, even if the other OptiBoarders who frequent the Ophthalmic Optics forum don't necessarily appreciate this stuff or find it especially interesting, the next poor guy out there trying to solve a similar optical engineering problem will have at least _one_ hit show up in his Google search. ;)

----------


## HarryChiling

That's funny a few months back a thread got me thinking about the same thing and I had a hard time finding a formula for it as well I searched high and low and through various books.  I am sure I could have found it in the OSA's Book, but I had already wasted too much effort on it at the time and just thought I'd move on.

I know how difficult a pull that one was and believe me if I could give you more than one positive in a row I would.

----------


## Darryl Meister

> I know how difficult a pull that one was and believe me if I could give you more than one positive in a row I would


Well, I certainly appreciate the positive feedback.

I ran across a similar problem trying to find a good algorithm for calculating the dominant wavelength for a set of CIE color coordinates a few months ago, while finishing up that Spectacle Optics program. There are literally dozens of forums out there with posts asking for the very same solution, and I never found a single response with a complete numerical recipe. And it took a fair bit of effort to put one together.

So, to dbracer's point, perhaps nowadays I'm just looking for an excuse to post this stuff...

----------


## HarryChiling

> So, to dbracer's point, perhaps nowadays I'm just looking for an excuse to post this stuff...


Better than an excuse not to. I saw you've been updateing your site, anything new.

----------


## Fezz

Hey...

Does this thread come with a study guide? Cliff notes? Instructions? A interperter?

;):cheers::bbg::cheers::shiner:

----------


## DragonLensmanWV

> Hey...
> 
> Does this thread come with a study guide? Cliff notes? Instructions? A interperter?
> 
> ;):cheers::bbg::cheers::shiner:


How about a "For Dummies" book?

Here's one observation about ABBE that I experience on a daily basis.
If I look at a fluorescent light fixture on the ceiling ( so what if I spend hours doing that? :D) through the edge of my lenses (Hoya 1.70) I can see at the top of the fixture the red fringe fading to yellow and at the bottom of the fixture I see blue fringe fading to black. Now looking at pictures or TV through the edge (the effects are less in the central portion) I see feature edges reproduced in a different color just offset from the original like if your newspaper's register is off so people look like thay have four eyes. Now with the Hoya 1.70 there is more  color blur at the blue end than the red end. With 1.67, I have only a very small area that is usable and everything looks fringed and the lenses are basically useless for me, so I counsel against 1.67 for powers that exceed + - 4D. Of course, below that range there is no need for the 1.67, so my usage of 1.67 is zero.

----------


## Darryl Meister

> Does this thread come with a study guide? Cliff notes? Instructions? A interperter?


In all fairness, it has always stated right at the top of this forum, _Not for the faint of heart!_

In all my years of moderating this forum, I've never seen so much balking at a little high-school-level algebra!  :Nerd:  For shame! ;)

I've decided to start a separate thread for dispersion equations because 1) I think this information is too valuable not to make available to those who might find it useful and 2) I do not want this thread on chromatic aberration in polycarbonate further derailed.

Harry, I would encourage you to post your own "first-order" (linear approximation) dispersion equation in this thread as well.

----------


## Fezz

Just having a little fun Darryl!

Just having a little fun...thats all!

:cheers::cheers::cheers:

----------


## dbracer

> In all fairness, it has always stated right at the top of this forum, _Not for the faint of heart!_
> 
> In all my years of moderating this forum, I've never seen so much balking at a little high-school-level algebra!  For shame! ;)
> 
> I've decided to start a separate thread for dispersion equations because 1) I think this information is too valuable not to make available to those who might find it useful and 2) I do not want this thread on chromatic aberration in polycarbonate further derailed.
> 
> Harry, I would encourage you to post your own "first-order" (linear approximation) dispersion equation in this thread as well.


Ah heck Darryl, you're probably right. 

I probably should keep my comments to myself since I like the formula stuff and will probably follow you to your new thread.

I can't be too smart. I'm a dang optometrist. Go figure. (That's a rhetorical remark, not a command).

dbracer,
The guy with the big mouth or at least too fast of keys

----------


## MarcE

> so I counsel against 1.67 for powers that exceed + - 4D. Of course, below that range there is no need for the 1.67, so my usage of 1.67 is zero.


1.70 transitions??
1.70 polarized??

I will admitt that Hoya has focused on high OPTICAL quality materials, CR, 1.56, Trivex, 1.60 and 1.70.

----------


## Fezz

> 1.70 transitions??
> 1.70 polarized??
> 
> I will admitt that Hoya has focused on high OPTICAL quality materials, CR, 1.56, Trivex, 1.60 and 1.70.



:cheers::cheers::cheers:

----------


## DragonLensmanWV

> 1.70 transitions??
> 1.70 polarized??
> 
> I will admitt that Hoya has focused on high OPTICAL quality materials, CR, 1.56, Trivex, 1.60 and 1.70.


Got 1.60 in both.:D

Can't wait until Trivex polarized, and a 1.70 photochromic would be nice. Maybe Armorlite could wed Instashades with 1.70.

----------


## Fezz

I assume a case could be made that any medium for which light passes could cause acuity loss.

----------


## DragonLensmanWV

> I assume a case could be made that any medium for which light passes could cause acuity loss.




<muttering> Durn ol' air causing me acuity loss.:angry:






:D

----------


## Darryl Meister

> I assume a case could be made that any medium for which light passes could cause acuity loss


Certainly, any "real," homogeneous optical medium will at least 1) reflect some degree of light at boundary interfaces and 2) disperse light, both of which can degrade the quality of the image. Absorption and light scatter can degrade the image quality even further. But the effects have to be rather significant before visual acuity is noticeably affected. Keep in mind that the "just noticeable difference" for a typical observer is roughly 0.25 D, which actually represents a considerably greater reduction in contrast and image quality than the presence of low levels of these other effects.

----------


## Fezz

> Keep in mind that the "just noticeable difference" for a typical observer is roughly _0.25 D,_ which actually represents a considerably greater reduction in contrast and image quality than the presence of low levels of these other effects.


I assume that we can then make the argument about the above! If you combine the effects of power, material, index, abbe, etc with possible variances in the refractive findings on any giving day, we can open up a whole hell of a  Mighty Pandora's Box!!

When is Barry going to chime in?

;):cheers::D

----------


## sharpstick777

The whole question of losing 2 lines of resolution comes down to what measurement or chart you are using (you have to define your "line").  This entire discussion assumes we are talking about the Snellen Chart which is for measuring Visual Accuity only not resolution.  There are other charts for Resolution such as the Koren, USAF 1951 and the I3A/ISO.  

Poly is unlikely to drop a line in the Snellen Chart, but very likely to in tests specifically designed to test Resolution.  So if the lab tech in Reply 1 is talking about those charts that refer specifically to Resolution he could be correct.  

I think we all know that this question is both subjective and objective.  I have a -10.0 pt who loves poly, and a minus -1.0 pt who doesn't.  

We ALL know that Poly is not the best optically, and we ALL know that most patients won't notice the difference.

All I know is that I need another Calculus class.  

Sharpstick

----------


## Darryl Meister

> The whole question of losing 2 lines of resolution comes down to what measurement or chart you are using (you have to define your "line"). This entire discussion assumes we are talking about the Snellen Chart which is for measuring Visual Accuity only not resolution.


In the United States, at least, more often than not we're referring to the classic Snellen chart, unless we're dealing with a research environment. For corrected acuities in the 20/20 range, adjacent Snellen lines would typically represent +/-5 feet. This represents a difference of roughly +/-1 minute of arc, give or take.




> We ALL know that Poly is not the best optically, and we ALL know that most patients won't notice the difference... I think we all know that this question is both subjective and objective. I have a -10.0 pt who loves poly, and a minus -1.0 pt who doesn't.


This is a good point to make, particularly given the relatively small number of individuals who really fall into the higher prescription category generally associated with meaningful levels of chromatic aberration. Of course, your comment regarding subjective observations also alludes to the _potential_ for symptomatic wear even in lower prescriptions. It's definitely difficult to generalize...

----------


## chip anderson

Never overlook the fact that 20/happy is interchangable with 20/not complaining. This is a very fine line that I don't think gets the attention it deserves. I know OMD's who put as many of thier patient's as possible in O.U. Rx's for contacts thinking that thier patient's appreciate the convienence of not being able to get them mixed up, more than the best vision they can get.

Same could be said for poly usage....

Bad medicine, bad bad medicine....


Chip

----------


## Barry Santini

> When is Barry going to chime in?
> ;):D


Well, for me, its more about some of the factors that are either assumed, or not understood:

1. Does the given Rx really represent maximum acuity, i.e., full DV and astigmatism/axis correction...(you never know)
2.What has been the "habitual" vision/RX? We're keenly sensitive to comparative judgments, and humans often come to erroneous conclusions about what "looks" better, (at least at first)
3. Darryl's stuff on opticampus about chromatic aberration is great, but needs to be taken further.  Yes, our eye has significant axial chromatism.  Yet, when even an emmetrope looks at the full moon, does he/she see color fringing? No.  Why? neurological adaptation. 
4. Same goes for the inherently decenterd optics of the human eye.  It has significant mirror coma, but do you notice? No. Why? Neurological adaptation.
5. The wallies of poly:  Anyone on the board whose has one of Dr. Morrison's Enigma/Countour optics eyewear (Darryl, just why did Zeiss trash this great technology?  Was it NIH?), knows that there is no lateral color error with these lenses, made from poly.  I really believe it is the industry's fasination with Flat lenses that exacerbates lateral color with poly. And yes, I know that higher index lenses should be flatter form for maximum axial correction and sharpness

It really comes down to contrast: who has it, and who doesn't.

Barry

----------


## Fezz

> 5. The wallies of poly: Anyone on the board whose has one of Dr. Morrison's Enigma/Countour optics eyewear (Darryl, just why did Zeiss trash this great technology? Was it NIH?), knows that there is no lateral color error with these lenses, made from poly. I really believe it is the industry's fasination with Flat lenses that exacerbates lateral color with poly. And yes, I know that higher index lenses should be flatter form for maximum axial correction and sharpness
> 
> It really comes down to contrast: who has it, and who doesn't.
> 
> Barry


 
Sidenote / thread Hi-Jack-

My pair of Enigmas is just about DOA. The lenses have spider cracked so bad, that I can't keep them tight, and the scratches.......well, lets just say that I put the AR to the test! I will miss them when they are gone!
:cheers::cheers::cheers:

----------


## Darryl Meister

> 3. Darryl's stuff on opticampus about chromatic aberration is great, but needs to be taken further. Yes, our eye has significant axial chromatism. Yet, when even an emmetrope looks at the full moon, does he/she see color fringing? No. Why? neurological adaptation.


Adaptation plays a role, but keep in mind that the lateral chromatic aberration of the eye, which is responsible for color fringing, is not as significant as the axial chromatic aberration of the eye, particularly since the sensitivity of the retina drops off rapidly away from the fovea.




> (Darryl, just why did Zeiss trash this great technology? Was it NIH?)


Unfortunately, it was extremely difficult and expensive to mold and edge these lenses. So, given the market demand for the product at the time, it wasn't really cost-effective to continue making them.

----------


## Barry Santini

> Adaptation plays a role, but keep in mind that the lateral chromatic aberration of the eye, which is responsible for color fringing, is not as significant as the axial chromatic aberration of the eye, particularly since the sensitivity of the retina drops off rapidly away from the fovea.
> 
> 
> Unfortunately, it was extremely difficult and expensive to mold and edge these lenses. So, given the market demand for the product at the time, it wasn't really cost-effective to continue making them.


Thanks again, for your thoughtful response. I'll concede that an extended object like the moon is influenced by lateral chromatism. But, a star (being a point) is not. And no one I know sees color fringing, naked eye, on stars (axial chromatism).

Shame about the Contour optics. They certainly have a more imprtant place in our fieled than yet another free-form progressive, IMHO.

Barry

----------


## Darryl Meister

> not. And no one I know sees color fringing, naked eye, on stars (axial chromatsim).


Color fringing from lateral chromatic aberration of the eye is actually visible, but we are generally just unaware of it. If you move a card slowly over your pupil while staring at the edge of a white, brightly illuminated window sill, for instance, you can observe your own lateral chromatic aberration. Although I've never given it too much thought, I suspect that the transverse effects of ocular chromatic aberration would normally be perceived more as a reduction in image contrast, not as color fringing, since the defocused images of each color would still overlap to some extent.

In any event, the eye has several mechanisms in place to minimize this and other aberrations:

1) The sensitivity of the retina drops off rapidly away from the fovea; at only 5 degrees from the fovea, visual acuity has already dropped by roughly 66%, which reduces the chromatic aberration effects for larger or extended objects.

2) The Stiles-Crawford effect results in significantly less sensitivity for rays of light refracted through the periphery of the pupil, which reduces the chromatic aberration effects due to prismatic displacement away from the optical axis of the eye.

3) The relative sensitivity of the eye drops off rapidly away from the center of the visible spectrum, leaving the eye considerably less sensitive to red and blue colors and to chromatic aberration effects in general.

Of course, I guess you could think of one or two of these as a form of neurological adaptation in the evolutionary sense, anyway.

----------


## Barry Santini

> Color fringing from lateral chromatic aberration of the eye is actually visible, but we are generally just unaware of it. If you move a card slowly over your pupil while staring at the edge of a white, brightly illuminated window sill, for instance, you can observe your own lateral chromatic aberration. Although I've never given it too much thought, I suspect that the transverse effects of ocular chromatic aberration would normally be perceived more as a reduction in image contrast, not as color fringing, since the defocused images of each color would still overlap to some extent.
> 
> In any event, the eye has several mechanisms in place to minimize this and other aberrations:
> 
> 1) The sensitivity of the retina drops off rapidly away from the fovea; at only 5 degrees from the fovea, visual acuity has already dropped by roughly 66%, which reduces the chromatic aberration effects for larger or extended objects.
> 
> 2) The Stiles-Crawford effect results in significantly less sensitivity for rays of light refracted through the periphery of the pupil, which reduces the chromatic aberration effects due to prismatic displacement away from the optical axis of the eye.
> 
> 3) The relative sensitivity of the eye drops off rapidly away from the center of the visible spectrum, leaving the eye considerably less sensitive to red and blue colors and to chromatic aberration effects in general.
> ...


Although I haven't personally done the pupil test you describe, it does make sense. When I worked for Tele Vue optics, we used to regularly *sample* portions of the exit pupil of eyepieces to observe and corroborate design tradeoffs we made. However, anything other than an artifical star point is considered an extended object, and you are right, you would be sampling lateral color. But, axial color (and the eye's coma from its decentered optics) has been compensated by evolution as it tries to reduce/prevent neural fatigue.

Interesting discussion...I think you're right, these effects are part of neural adaptation (& I'm thinkin' I'm a little rusty here).

barry

----------


## Barry Santini

> Unfortunately, it was extremely difficult and expensive to mold and edge these lenses. So, given the market demand for the product at the time, it wasn't really cost-effective to continue making them.


Honestly, I worn and tried alot of lenses myself, and nothing, _nothing_ produced a "WOW" factor as much as the Contour optics (MUCH better than my new Hoya NuLux EP).

FWIW

Barry

----------


## Fezz

Could any of you Ultra Bright Folks educate a simpleton like me as to where I could read up on neural adaption?

Thanks!

;):cheers: :Cool:

----------


## Darryl Meister

> Interesting discussion...I think you're right, these effects are part of neural adaptation (& I'm thinkin' I'm a little rusty here).


I'm just glad to have a few people on this 'Board who are interested enough in this stuff to be able to banter back and forth about it. I often say the same of Harry C. in the various ophthalmic optics threads.




> Could any of you Ultra Bright Folks educate a simpleton like me as to where I could read up on neural adaption?


Although it doesn't focus specifically on neurological adaptation, I generally recommend Tunnacliffe's _Introduction to Visual Optics_ for those genuinely interested in vision science and visual optics. Michaels's _Visual Optics and Refraction_ is also a great text, although it is now long out-of-print.

----------

