Author Topic: An Anecdote About Visual Acuity  (Read 3235 times)

Offline ZC

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An Anecdote About Visual Acuity
« on: June 29, 2014, 04:04:34 PM »
When I was a high-school kid I read a blurb about Bates in the Whole Earth Catalog. I made a mental note and turned the page. My vision then was similar to my vision now: -5.0 / -6.5.

After I graduated college, I traveled across North America in the summer. Early in the summer I lost the glasses that I used every day when I was on an inner in a river in Iowa. A month later I lost my spare pair of glasses when I was backpacking in the Canadian Rockies. I was hopping across rocks to cross a stream and the glasses fell off my sweaty face into the stream and over a waterfall.

I was an experienced backpacker at the time and had a trusted friend with me, so I continued my camping trip without my glasses. Once we completed the journey and got back to our car, we drove to Victoria, on Vancouver Island where I went to an optometrist, who measured my vision and made me some new glasses. This was way before there were cell phones or personal computers, so I had no idea how the prescription for these new glasses compared to the glasses I had been wearing.

From Vancouver Island we went to Chicago, where I started a new job as an inspector in a machine shop. There was some near work but not a ton of it. Mostly I walked along the factory floor and measured the dimensions of metal parts. Back then there were no computer monitors. I did read a bit when I was not working but I was not spending many continuous hours doing near work each day.

After a couple of weeks in Chicago, I noticed that when I waited for the bus to go to or from work I could no longer read the bus number. Having read about Bates all those years earlier, I knew immediately what had happened: my eyes had strengthened during the week or so that I had worn no glasses. Therefore the Victorian optometrist gave me a weaker Rx. Then I went back to wearing my glasses virtually every waking minute in Chicago and my eyes reverted to their more myopic state. I went again to an optometrist and I had my eyes measured again and bought another pair of glasses. This new Chicago prescription was probably identical to the one that I had before my backpacking experience because it remained stable over many years into the future.

There is a point to this story. It seems to defy what I often read when people write about rehabilitating myopia. Let's break down my experience into two parts:

1. wearing no glasses for a little more than a week significantly improved my visual acuity (probably by more than 1 full diopter), and
2. wearing my new, weaker glasses quickly caused my improved vision to degenerate, reverting to its previous state.

The first point seems to conflict with claims that I often read stating that if the eyes are given too stressful a stimulus, they will not adapt. Therefore, the claim goes, correction should not jump from -6.5 to 0. Rather, they say, one should gradually change the correction. Say, for example, -6.5 to -6.0. Yet my n=1 experience seemed to suggest that significant improvements in visual acuity are possible in just a few days by providing significant visual stress. It raises the question of whether even greater improvements would be possible through the use of plus lenses on high myopes. After all, if -6.5 to 0 worked pretty well, maybe -6.5 to +1.0 could work better.

The second point seems to confirm that a small stress (1.25 D, say) provided a stimulus insufficient even to maintain the gains that I had acquired by using the very large stress (6.5 D). With the small stress my eyes became more myopic while with the large stress they became less myopic.

I recognize that my anecdote is merely an anecdote and it in no way resembles any kind of controlled experiment. There are all kinds of confounding variables: I was outdoors more when I was without glasses; and I probably did more near work when I wore the new glasses.

But from these experiences I believe that I am justified in holding two beliefs about my vision as a much younger person:

A. Large visual stresses can cause significant visual improvement in a short time period (days, rather than weeks), and
B. Gradual undercorrection alone is insufficient to bring about visual improvement.

I would be happy to hear from those who have alternative explanations of what happened to me.

(By the way, this all happened in 1978. Ever since then, I have mentioned it to every optometrist, optician, and opthalmologist who has examined me. I always ask them what they think happened. Every single one has refused to give me an answer. Essentially, they shrug their shoulders. Maybe they figure it's bad for business to tell the patient you think that he is crazy.) :o

(I should also add that I now have to stand at a desk at work five days a week and drive a car there and back. So, I have no opportunity to go seven consecutive days without glasses. So, I do use glasses that are undercorrected by 0.5 diopters at a time. But I do what I can to spend some time without glasses.)

Offline kenS

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Re: An Anecdote About Visual Acuity
« Reply #1 on: June 29, 2014, 04:35:51 PM »
Interesting story.  There seems to be differing opinions on which is the best methodology.  I am thus a bit confused as to which one I should follow.
I'm trying right now to not wear my glasses as much as possible.  When reading, I try to read at either edge of blur (D2 using Todd's terminology) or slightly further than that (dipping into D3).  The problem I have is that both the book and my head are always slightly moving, so I'm always moving in between D2 and D3 throughout my reading of the page. But what I'm not sure of is whether simply reading at this distance is what is supposed to be therapeutic or whether I ought to be actually staring at a word for 30 minutes waiting for clearing to take place.

This is all a bit confusing.  Hopefully some of what I'm doing is helping and I'll get lucky. :-\


Offline ZC

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Re: An Anecdote About Visual Acuity
« Reply #2 on: July 01, 2014, 04:57:54 PM »
The first post in this threat refers vaguely to "people" who make claims that appear to contradict my personal experiences. Since I did not give specifics, it would be reasonable to wonder if I was attacking a "straw man," that is, I was criticizing claims that no one actually made.

Although no one accused me of this, here is how I would fashion a response.

The person who sometimes writes under the name "Alex Frauenfeld," says:
Quote
Not wearing any glasses = Visual cortex signal error = Strain
Strain = increased risk of more myopia
bates-method-no-glasses-vs-glasses-the-blur-horizon.

Of course the statements quoted are false if one interprets the equals sign to mean something like "is equal to." Clearly that was not the author's intent, however. Rather, I believe, he meant to express the thought that we get if we interpret the equals sign to mean something along the lines of "is the cause of." The causal relation, like the equality relation, is transitive, so Frauenfeld is committed to the claim that:

    Not wearing glasses causes an increased risk of worsening myopia.  [1]

My experience was that not wearing glasses caused the lessening of my myopia. My experience is in direct conflict with claim [1], above.

David De Angelis makes a similar claim:

Quote
The load or the training stimulus imposed on the eye's focusing capacity must be efficient; that means neither too excessive nor too little. The best training effect is achieved by having minimum fogging, when the letters or the object you are focusing on are slightly out of focus.

Excessive fogging may cause the opposite negative effect, worsening either myopia or hyperopia. The reason might be that in the case of an excessive stimulus, focusing becomes impossible without even having a try at all.
(pages 50-52, locations 871-875, The Secret of Perfect Vision, English Translation, Kindle edition)

De Angelis clearly endorses the claim [1], above.

It is somewhat odd that De Angelis adopts this position because he describes research from Hung et al., in which monkeys were forced to wear either +6, +3, 0, -3, or -6 lenses for 72 to 113 days (page 35). The monkeys with plus lenses experienced a shortening of their eyes' axial lengths and the ones with minus lenses had increases in axial lengths. De Angelis cites this study approvingly, yet the researchers appeared to make what De Angelis would deem to be the cardinal error of applying an excessive stimulus.

Admittedly, this is a monkey model. But De Angelis seems to believe that it is legitimate to use such data to draw conclusions about human vision. I tend to agree, based on our shared evolutionary ancestry. So, if large, discontinuous changes in defocus change monkeys' refractive status, it seems reasonable to suppose that they could do the same in human beings.

(Just so that no one is confused, I state openly that I believe that many of the claims made by Bates are false. I am not trying to defend or criticize any individual person. Rather, I am attempting to test the claims I read about vision rehabilitation, so that I can distinguish those claims that are well-supported from those that are not, regardless of who formulated those claims.)

Offline Alex_Myopic

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Re: An Anecdote About Visual Acuity
« Reply #3 on: July 02, 2014, 04:11:17 AM »

It is somewhat odd that De Angelis adopts this position because he describes research from Hung et al., in which monkeys were forced to wear either +6, +3, 0, -3, or -6 lenses for 72 to 113 days (page 35). The monkeys with plus lenses experienced a shortening of their eyes' axial lengths and the ones with minus lenses had increases in axial lengths.


I don't remember if this was the same research that I posted before (my source was the myopia manual) but in that survey those who wore high plus (like +6D) had no improvement or became more myopic.

Offline ZC

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Re: An Anecdote About Visual Acuity
« Reply #4 on: July 02, 2014, 07:38:24 AM »
It doesn't sound like the same journal article since De Angelis claims that all the plus lenses moved the monkeys further towards hyperopia.

Offline OtisBrown

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Re: An Anecdote About Visual Acuity
« Reply #5 on: July 02, 2014, 10:05:03 AM »
Hi ZC,

I have read the report by Dr. Smith.  A "high plus" simply "saturates" the accommodation system.  But what it very important to understand is that the young natural eye is responsive IN BOTH DIRECTIONS - to a mild + and - 3 diopter lens (when measured as a refractive STATE).

This does not "prove" anything in a "medical sense", so the dynamic nature of all natural eyes - is ignored.  The ODs and MDs state that this type of objective science does not mean anything, because the "primate eye" data never behaves like the human eye.  In this case, I would not say, "hyperopia" that is biased and presumptive.  What is measure is a "change in refractive state".  The "length change" is assumed.

http://www.ocf.berkeley.edu/~wildsoet/images/pos_lens_induce_hyperopia.swf

As an engineer, I also look for "symmetry" of response - as shown here:

http://www.ocf.berkeley.edu/~wildsoet/images/neg_lens_induce_myopia.swf

If the natural eye did not do this, I simply would not publish anything, nor would I suggest that prevention is possible, when a person still reads the 20/40 line.

I disagree with ODs - but that is the difference between objective science - and the desire to "satisfy" the general pubic with a strong minus lens - in a few minutes.

I do  not "fault" them either, because nothing else "works" for them.  I just want the knowledge to protect my distant vision myself - because I know that they can not do that for me.


It doesn't sound like the same journal article since De Angelis claims that all the plus lenses moved the monkeys further towards hyperopia.
« Last Edit: July 02, 2014, 12:37:23 PM by OtisBrown »

Offline ZC

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Re: An Anecdote About Visual Acuity
« Reply #6 on: July 03, 2014, 10:55:37 AM »
There is nothing like writing down one's thoughts to make them clearer. I now realize that my opinion, as expressed in this thread conflicts as well with claims made in this forum by Todd Becker. If I understand Todd's position, it goes something like this:

1. The retina has substantial thickness.
2. Axial length changes only when focused images fall somewhere between the retina's front and back surfaces.
3. Therefore, focused images that fall in front of the retina or (virtually) behind it do not cause axial length changes.
4. Large deviations from emmetropic lens power cause images to fall either in front of the retina or behind it.
5. Therefore, large deviations from emmetropic lens power do not cause axial length changes.

I think that Todd is the model of an open-minded scientist. I certainly aspire to have as critical an approach as he. But I have a lot of trouble reconciling my personal experience with the conclusion expressed above. Of course, I can always come up with a just-so story to explain what happened to me.

Maybe when I was backpacking for a week, all the shortening of my axis was caused by the times when I was using my eyes to view objects between D2 and D3. This seems implausible to me, because most of my days were spent walking and even my feet are beyond D3. Yet, the implausible is sometimes possible.

I have a harder time explaining why the Rx I got after backpacking caused my eyes to deteriorate and the RX I got after living in Chicago remained stable for years.

The Rx after backpacking, according to Todd's hypothesis, caused the focused image to fall within the retina layer. Let us assume, that continued use of this weaker Rx led my eye gradually to lengthen. As it lengthened, the focused image would now move closer to the front of the retina. This should have signaled my sclera to stop the axial lengthening and led to a stable axial length. Instead, my axis continued to lengthen until the focused image moved in front of the frontmost layer of the retina.

I used the word "anecdote" in the title, because that is exactly what it is. I wonder if my experience is an anomaly.

Offline Ydgrunite

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Re: An Anecdote About Visual Acuity
« Reply #7 on: July 03, 2014, 01:37:10 PM »
1. The retina has substantial thickness.
"Substantial" is not a very precise term.  Although wikipedia says that the retina is 0.5 mm thick, it does not refer to a source.  I found better sources that place retinal thickness closer to 0.2 mm.  Entire axial length might be 24 mm for an emmetropic eye.  With the rule of thumb that 1 mm of axial length relates to 3 D of refractive power, that makes for a range of about 0.6 D to move a image across the whole retina.

2. Axial length changes only when focused images fall somewhere between the retina's front and back surfaces.
Why would axial length change when the focused image falls within the retina?  That is exactly where you want it to fall.  That is when you see a sharp image.  There is no stress on the eye when you see a sharp image.

3. Therefore, focused images that fall in front of the retina or (virtually) behind it do not cause axial length changes.
I thought that the whole point of the Getting Stronger website was to say that stress induces change.  If the focused image falls in front of the retina, this causes far stress and shortening of the eye.  If the focused image falls behind the retina, this causes near stress and lengthening of the eye.

4. Large deviations from emmetropic lens power cause images to fall either in front of the retina or behind it.
Yes.

5. Therefore, large deviations from emmetropic lens power do not cause axial length changes.
Deviations from emmetropic lens power do cause axial length changes, but other recent discussions on this board cite studies that show the deviation cannot be too large, otherwise it has no effect.  Your retina can detect which way it has to move to reduce bluriness within a certain range, but beyond that it is too blurry to detect required direction.

Offline ZC

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Re: An Anecdote About Visual Acuity
« Reply #8 on: July 03, 2014, 06:14:56 PM »
Ydgrunite,

Thanks for you responses.

My tentative position, as I've outlined in the posts in this thread, is in agreement with your responses to the first four claims. My position, based on my personal experiences, is that extreme defocus led to a diminution of my myopia.

What I was trying to determine was whether I was fairly describing Todd's position.

For example, here is what Todd wrote in one of his blog posts:

Quote
The retina is not single plane, but rather a tissue of some depth, consisting of multiple layers of sensitive photoreceptors cells (rods and cones) and intermediate conductive fibers. In fact, the photoreceptors perversely evolved for various reasons to be at the back of the retina, with the “wiring” actually in front of them.  But the photoceptors are distributed over multiple layers. Presumably, the most active receptors are those which are usually stimulated by well-focused images.  After all, those are the ones whose signals the brain can interpret, and they receive the most reinforcement.  For a myope, these will tend to be the receptors in the focal plane of close objects, toward the back of the retina. Because the myope is doing a lot of close work and spends less time looking in the distance, the closer retinal cells get less stimulation and suffer from underuse.  However, if these closer layers can gradually get more stimulation, or example by using plus lenses, they will adapt to increase in sensitivity and the strength of their signalling to the visual cortex will gain prominence.  At some point, weak signals from this forward layer (on which there is a sharper image) will be sent simultaneously with the stronger signals form the backward layer (on which the images are blurred).  During the period of adaptation, activation of multiple layers will be perceived as a double-image. Eventually, and with time, the sharper forward layer will dominate over the backward blurry layer.  And as the overall shape of the eye is remodeled as the eye grows in response to focusing on distant objects, the focal “strain” on the eye will be reduced, and a new equilibrium shape will take hold. This hypothesis is unproven, but is consistent with known mechanisms, and could be tested experimentally.
http://gettingstronger.org/wp-content/plugins/wordpress-toolbar/toolbar.php?wptbto=http%3A%2F%2Fgettingstronger.org%2Frehabilitation%2F&wptbhash=aHR0cDovL2dldHRpbmdzdHJvbmdlci5vcmcvMjAxMC8wNy9pbXByb3ZlLWV5ZXNpZ2h0LWFuZC10aHJvdy1hd2F5LXlvdXItZ2xhc3Nlcy88d3B0Yj5JbXByb3ZlIGV5ZXNpZ2h0ICYjODIxMTsgYW5kIHRocm93IGF3YXkgeW91ciBnbGFzc2VzPHdwdGI%2BaHR0cDovL2dldHRpbmdzdHJvbmdlci5vcmc8d3B0Yj5HZXR0aW5nIFN0cm9uZ2Vy

Specifically, this quotation provides some textual support for:

1. The retina has substantial thickness, and
2. Axial length changes only when focused images fall somewhere between the retina's front and back surfaces.

From 2, it follows that:

3. Focused images that fall either in front or behind the retina do not stimulate axial length changes.

As Todd describes the process, it is necessary that a focused image fall somewhere within the retina's thickness. You object that a focused image on the retina cannot stimulate remodeling. I presume that Todd's response would be that the remodeling is triggered by the focused image's location within the retinal layers. If the image focuses in the middle layer, there would be no stimulus to remodeli If the image focuses in a front or rear layer, there would be a stimulus to remodel.

Hung and Cieffreda discuss IRDT n this article:
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CCoQFjAB&url=http%3A%2F%2Fvisp.rutgers.edu%2FIRDT%2520of%2520Myopia%2520Development.pdf&ei=AAq2U9CvDI-ryATN3YC4Dg&usg=AFQjCNHddci5POkfjqJjF31vro2c1OpVIQ&sig2=ifbxBiLzttUbcligRNo4GQ&bvm=bv.70138588,d.aWw

I will need to read the article a few more times, but my initial impression is that the mechanism they propose in the linked article is different from the mechanism that Todd is proposing. In their article I think they are saying that the retina senses how the changes in axial length affect the changes in the radius of the blur circle. If the blur circle's radius is reduced (i.e., the image becomes more focused), the direction of axial length change continues. If the blur circle's radius is increased (i.e., the image becomes more unfocused), the direction of axial length change reverses. 

If I understand Hung and Cieffruda correctly, then this would mean that myopia rehabilitation does not require focused images to fall between the front and back layers of the retina. If that were the case, then your objections to claims 2 and 3 would be confirmed.

Offline ZC

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Re: An Anecdote About Visual Acuity
« Reply #9 on: July 04, 2014, 02:44:27 AM »
Tom and jimboston,

I very much appreciate your thoughtful comments. I welcome considering differing opinions and welcome hearing from people who disagree with my opinions. What I aim for, and what I think that jimboston has provided a model for, is conceptual clarity.

The addition of a separate causal pathway would explain why in some cases large deviations from emmetropic lens power improve visual acuity and in other cases large deviations from emmetropic lens power do not improve--and may even worsen--visual acuity.

Thank you!