Wow -- any eye experts out there?

Tom Hoskinson · May 31, 2007

Roger Hicks said:
Wow... like... shit, man. Why'd nobody tell me? I mean, uhhh, yeah...

(2000 words deleted here)

But I'm pretty sure I have some of those glasses somewhere in the studio. I'll try it too.

Cheers,

R.

I have a big box of the disposible Red/Cyan glasses in our microscopy lab at work. We make a lot of SEM anaglyphs and nanofocus Xray anaglyphs.

For Red/Cyan glasses See: www.anachrome.com

Earl Dunbar · May 31, 2007

Roger Hicks said:
Wow... like... shit, man. Why'd nobody tell me? I mean, uhhh, yeah...
<snip>
Cheers,

R.

OMG, one of the funniest posts I've seen!

But take heart, Roger ... In my retirement my major objective will be to reintroduce the 60s to my world. Ta-hell with anyone who doesn't understand! You're free to join the new commune.

Earl Dunbar · May 31, 2007

DrPablo said:
And you might accomodate the difference in brightness by dilating the pupils more -- so the effective light entry would be unchanged.

But then (with pupils dialated), acuity would be reduced, no?

On my next visit to my optometrist, I will seriously investigate IZon technology for what they tout as as "High Definition vision".

As of my last email exchange with my optometrist, the technology may not yet be ready for progressive contacts, so I may just end up waiting or getting it just for my spectacles. I will have a discussion with her regarding how/whether such a technology would enhance focusing with my rangefinders, SLRs and the 4x5. BTW, she's the coolest optometrist I've ever had.

DrPablo · May 31, 2007

Earl Dunbar said:
But then (with pupils dialated), acuity would be reduced, no?

I don't think so for a few reasons (though I'd be interested to hear other thoughts):

1) resolution, whether you're an eyeball or a camera lens, depends on your ability to discriminate contrasting details, and you need to regulate exposure via your pupil diameter in order to do that

2) the pupil does diffract light, and diffracts more heavily at narrower apertures

3) when focusing on close objects you physiologically dilate your pupils to focus (termed accomodation)

Now, your depth of field might change, but I don't think that matters because the angle of view of the fovea is very narrow. And our eyes aren't taking still pictures -- we have rapid movements of the eyes called saccades that dart around to different subjects of interest, and that makes the instantaneous DOF not so important.

You may be right that at full (or excessive) pupillary dilation acuity falls, but that may be a matter of acuity being impeded by an exposure problem.

So for the above situation with the yellow glasses at night, you have to dilate your pupils in order to maintain the ability to see if you effectively cut exposure to your eyes. Your pupils are making up for the "filter factor" of the glasses, lest they underexpose and you crash because you can't see.

AgX · Jun 1, 2007

AgX said:
...ones scoptic vision (with a peak at 520nm)...

It is 505nm and scotopic.

(Glasses were not working...)

AgX · Jun 1, 2007

Vaughn said:
If I look at some printed material in which there is red lettering on a white or black background, the red letters seem to be 3D...to stand up off the page. Closing one eye eliminates this effect.

I suspect that my two eyes do not register color in the same way -- and the difference acts like a stereo viewer for those 3D photos of old. Equally plausible is that I'm nuts.

Vaughn

Nuts too...

I remember experiencing this with blue on black and as far as I remember also with lettering in another colour. But never on white. With me this effect is rather situation depending, I guess rather due to a contrast effect, however with black base only.

MattKing · Jun 1, 2007

You realize that there are a whole bunch of APUG members reading this thread, thinking about it, and alternately winking at there computer screens - first left eye, then the right, etc., etc. ...

Matt

AgX · Jun 1, 2007

I close my eyes and count to ten,

as Dusty Springfield sang in those days...

Roger Hicks · Jun 1, 2007

Earl Dunbar said:
But take heart, Roger ... In my retirement my major objective will be to reintroduce the 60s to my world. Ta-hell with anyone who doesn't understand! You're free to join the new commune.

Now THERE'S a cause worth demonstrating for. I can see us now in our 90s:

"WE shall not...
WE shall not be... uh... what was it we weren't going to be, Earl?"

But to return to the thread, the French used to be required by law to have yellow headlights on their cars, precisely because this allowed maximum resolution and minimum dazzle. English drivers crissing the Channel were required to paint their headlamps with a sort of yellow mail-varnish so as not to damage sensitive French retinas. I don't know when the law changed but it's been many years now. Even so, you still see some new (or newish) cars with yellow lights, so evidently some still believe in it. The drawback, of course, is that one of the reasons it's less dazzling is that there's a lot less light...

Cheers,

Roger

ic-racer · Jun 1, 2007

APO correction lens for the Human EYE

I also am a MD and a physiologist. I thought you might be interested in this article which describes a corrective lens for the human eye. The goal is to eliminate the chromatic abarrasions of the human eye and essentially make the human eye an APO lens.

www.opticsexpress.org/viewmedia.cfm?id=90577&seq=0

Here is a image from the paper showing the theoretical effectiveness of the lens.

Vaughn · Jun 1, 2007

There you go...trying to confuse us with facts! (thanks, by the way...)

Now I am worried about parasitic aberrations whenever I put my glasses on. Can one get those parasites from unprotected sex?

Vaughn

jovo · Jun 1, 2007

Now, since I'm red-green perception deficient, I wonder if all the above affects me as it does those with normal color perception, or whether I actually might have some advantage in a safelight type environment. I have not been aware of any focus issues with my eyes in the darkroom nor that kind of 'pulsing' (for lack of a better or more correct word) that many experience with red against green or other combinations.....or at least not to the extent that others describe.

jovo · Jun 1, 2007

Roger Hicks said:
"WE shall not...
WE shall not be... uh... what was it we weren't going to be, Earl?"

Well, Roger, when you remember, there's ex lax....or immodium. Whatever...

greybeard · Jun 1, 2007

Dr. Pablo: when focusing on close objects you physiologically dilate your pupils to focus (termed accomodation)

Ummm...not to be overly picky, but when focusing on close objects, most of us physiologically distort our eyeballs to increase the lens-to-retina distance (termed accommodation). At least, we do when we are young. (At my age, we pick up a different set of glasses!)

With respect to the discussion regarding yellow glasses, tinted headlights and the like; blue light scatters more strongly from small particles than does light of longer wavelengths, and the reduction of what is called "veiling glare" (not the blinding reflection of a light source, but a general, overall reduction of contrast by scattered light) greatly improves visual acuity. This is one of the bases for yellow-tinted shooting glasses, and one of the best arguments for outlawing high-brightness bluish automotive headlights, which are particularly bad for older drivers with otherwise unnoticeable cataracts, or a lot of "floaters".

DrPablo · Jun 1, 2007

I had it backwards, we physiologically constrict the pupil during accomodation. Yes, there are other effects on the lens as well, but the pupil physiologically responds to close focusing. There are disease states in which there are errors in that -- classically, the Argyll-Robertson pupil in tertiary syphilis is when you constrict for accomodation but you don't constrict to bright light.

DrPablo · Jun 1, 2007

ic-racer said:
I also am a MD and a physiologist. I thought you might be interested in this article which describes a corrective lens for the human eye. The goal is to eliminate the chromatic abarrasions of the human eye and essentially make the human eye an APO lens.

Dead Link Removed

Here is a image from the paper showing the theoretical effectiveness of the lens.

Thanks for the great link. Boy, it reminds me how hard it is to read papers that are far outside my subspecialty. I'll pore over it in more detail, but I wonder why apochromatic lenses would be an engineering goal if physiologically we're achromatic.

Earl Dunbar · Jun 1, 2007

Dr. Pablo/Paul: Thanks. I was thinking of DOF, not resolution. But I do notice that under dim interior lighting (hence when my pupils are dilated), acuity seems to be decreased, whether for reading or resolving distant details, such on a distant LCD television screen, etc.

The iZon lens technology I am contemplating is claimed to use wavefront technology (as has been used in laser and other similar types of corrective surgery) to create a very thin lens which corrects for each eye at a very "low level", if you will. These lenses are encapsulated in the spectacle lenses, thus giving better correction and addressing distortion especially for night driving, etc. While that benefit is of interest to me, the possibility of better correcting CA and other problems for normal daytime vision, and how it might help in focusing a camera, really intrigues me.

ic-racer: Thanks for that link, I will read it with interest.

DrPablo · Jun 1, 2007

Earl,

I'm pretty sure that under dim lighting, a decrease in acuity will be largely explained by lighting and contrast factors. This will be particularly true if our eyes are adjusted to a bright light source, but we are trying to resolve things that are more dim.

On the other hand, your ophthalmologist is going to test your visual acuity before dropping in the pilocarpine or whatever it is they use to dilate your eyes. Certainly when you're pharmacologically totally dilated things look blurry, though I'm not so sure that's a problem with DOF as opposed to other pharmacologic effects of the eyedrops and/or difficulty with accomodation.

That iZon is worth thinking about for the next time my prescription changes, which based on past history will be somewhere in the next 14 seconds.

greybeard · Jun 1, 2007

I learn something new every day. I had the impression that Dr Pablo was referring to constriction of the pupil (opening through the iris) during focusing, avelength) then the eye which didn't sound right, so I popped over to Wikipedia (some authority, eh?) and found that

"Accommodation is the process by which the eye increases optical power to maintain a clear image (focus) on the retina. The principal focusing ability of the (terrestrial) eye is due to the difference in refractive index between air and the curved cornea, but the variable curvature of the lens allows for an additional adjustment. This varies from a maximum of over 15 diopters in an infant to only about 1.5 diopters in a person 70 years old, as the lens becomes less flexible with age."

I'm sure about the "less flexible with age" part, but was surprised to find that the accommodation issue has to do with the lens, and not the eyeball. This would certainly explain the differences in vision as a function of color, if the eye has more chromatic aberration than it can accommodate.

I always knew that monochrome had more advantages than I could explain...

Earl Dunbar · Jun 1, 2007

Paul: I often use other liquid substances for self-dilation. Amazing the bokeh I can get, not to mention multiple images. I don't need no steekin' Spiratone prism filters!

DrPablo · Jun 1, 2007

greybeard said:
I learn something new every day. I had the impression that Dr Pablo was referring to constriction of the pupil (opening through the iris) during focusing, avelength) then the eye which didn't sound right

The pupil does constrict during close focusing. That doesn't mean that that is the primary mechanism of focusing, but it's part of it. Take it for granted, it happens. It's a routine part of the physical exam, which is a routine part of my day. I reversed it in my post before because I was thinking about the whole Argyll-Robertson versus Marcus-Gunn pupil pathology which gets into efferent versus afferent defects and the neuroanatomy of the eye, which is hard to keep straight if you're not a neuroophthalmologist. But plain and simple, on physical exam, the pupils constrict on accomodation whether it makes intuitive sense or not.

Look under focusing here:

http://www.cf.ac.uk/biosi/staff/jacob/teaching/sensory/vision.html

Look down towards the bottom on this one:

http://cnri.edu/coursedemo/Pupils_and_Pupillary_Symptoms/Pupil_Reflexes.htm

ic-racer · Jun 8, 2007

DrPablo said:
The pupil does constrict during close focusing. That doesn't mean that that is the primary mechanism of focusing, but it's part of it. Take it for granted, it happens. It's a routine part of the physical exam, which is a routine part of my day. I reversed it in my post before because I was thinking about the whole Argyll-Robertson versus Marcus-Gunn pupil pathology which gets into efferent versus afferent defects and the neuroanatomy of the eye, which is hard to keep straight if you're not a neuroophthalmologist. But plain and simple, on physical exam, the pupils constrict on accomodation whether it makes intuitive sense or not.

Look under focusing here:

http://www.cf.ac.uk/biosi/staff/jacob/teaching/sensory/vision.html

Look down towards the bottom on this one:

http://cnri.edu/coursedemo/Pupils_and_Pupillary_Symptoms/Pupil_Reflexes.htm

Yes you are right on the miosis of the pupil on accomadation. It [miosis] is in fact from the parasympathetic nerves to the eyeball riding along with cranial nerve III. A little amazing that the accommodation(ie focusing & miosis) is all done with the autonomic nervous system. Somatic motor fibers in CN III just do the cross eye thing.

dslater · Jun 8, 2007

DrPablo said:
Thanks for the great link. Boy, it reminds me how hard it is to read papers that are far outside my subspecialty. I'll pore over it in more detail, but I wonder why apochromatic lenses would be an engineering goal if physiologically we're achromatic.

Hmm - I only briefly skimmed the paper, but the impression I got was that this is not intended to improve vision, rather it is intended to improve our ability to image a persons retina for diagnostic purposes.

Dan

DrPablo · Jun 8, 2007

Yes, you're right, though I was thinking about this interesting part of the introduction. I hadn't realized that correcting naturally occuring CA had been such a significant area of investigation.

Achromatizing the human eye by using refractive elements has been accomplished in the past in the visible range, exclusively for visual applications. Different lens designs have been proposed for this purpose. In this context, van Heel first presented a symmetrical triplet [27], based on experimental measurements of LCA accomplished by Ames and Proctor in only 3 subjects [28], reporting a subjective gain in vision when employing such a lens with polychromatic stimulus. The idea of a symmetrical triplet was also exploited by Bedford and Wyszecki [12]. The last achromatizing lens (AL) reported for the visible based on a triplet design was developed by Lewis and collaborators [29]. All of these mentioned lenses suffered from a rapid increase in TCA off-axis. In order to overcome this fundamental limitation,
particularly important when testing the lenses with extended polychromatic objects, Powel proposed the use of a more complex design to achromatize the eye, compounded by a triplet and a doublet air-spaced [30].

All these previous designs were intended to enhance vision, by introducing the opposite LCA found in the human eye.

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