Glossary and Q&A - Part IIf you have any suggestion or question that you think deserve to be here, I'm all ears. I myself have tons of questions to figure out, so I cannot be relied on in terms of addressing specific individual concerns.
GlossaryQ&A Personal Glasses Near Stress
Distance RangesAn object is said to be:
- in the near distance range if it's within 0 to 2 meters (equiv., 0 to 6.5 feet) from the observer
- in the middle distance range if it's within 2 to 4 meters (equiv., 6.5 to 13 feet)
- in the far distance range if it's beyond 4m (equiv., beyond 13 feet)
Having these terms at hand will help simplify several higher concepts in Far-Stress Method.
Far PointIf you're myopic, objects from far will appear blurry to you (with naked eyes), but if you move closer, and closer, the objects will become clearer, and then clearer. The far point is the farthest distance, such that you can still see objects in perfect focus. However, far point can be altered by wearing a prescription:
1) Wearing plus lenses decreases your far point.
2) Wearing minus lenses increases your far point.
Reading within your far point can increase your myopia, by inducing the so-called hyperopic defocus. The first step towards myopia reduction is to read beyond your far point, and undercorrected lenses can be very useful for that purpose.
HypnoticityEver notice some images appear clearer than others, despite both being located at the same distance from you? An image is called
hypnotic if it's perceived to have:
a) Well-defined contour
b) High contrast (i.e., dbrk under a light background; light under a dark background)
c) preferably, large and has only one color inside the contour
These properties make hypnotic image less effortful to focus on. Consequently, hypnotic images are perceived to be more "pleasant."
Different images vary in terms of hypnoticity. An example of a highly hypnotic image would be a big black circle under a white background.
It's possible to increase hypnoticity of an image, by getting closer to the object, or by increasing the intensity of light.
Who are you?A fellow human being researching myopia on his own, through:
- Self Experimentation
- Cramming on Research Studies/Theses/Books/Other Publications
- Brainstorming about Theories
What are your intentions behind your myopia advocacy?I have been diagnosed with myopia and given a prescription probably since I was around 8. I have been becoming more and more myopic since then. By the time I realized the harm full-time wearing of minus prescription has done to me, I was already around -8D.
I have then been trying to find solutions to stop/reverse myopia for almost a decade, and I only got some substantial breakthroughs fairly recently when I realized that myopia is primarily perpetuated by short focusing distance, and compounded by the wearing of minus lens.
Armed with these information, I know that I now have a duty to speak out - as there is the possibility that if I don't, the public might only be informed of our progress on myopia decades later. Since the Web is full of not-so-correct information, I knew that people suffering myopia deserve better - The Compendium on Myopia Rehabilitation is my way of providing accurate and up-to-date information that adheres to my own standard.
Being a person with high myopia, I have seen the profound effects of myopia on my own well-being. I certainly don't want history to repeat itself for millions of other people, and the Compendium represents my contribution in eradicating the myopia epidemic.
Where can I find practical and accessible information about astigmatism (and cylinder lens)? What are the pros and cons of pinhole glasses?A minus reading prescription provides clarity by
re-projecting light onto (and around) the retina. The downside of this approach is some bundles of light could be projected behind peripheral retina, thereby inducing peripheral hyperopic defocus.
An alternative way to obtain clear vision, during close work, is through the use of pinhole glasses. Contrary to the mode of action of a minus lens, pinhole glasses ensure that light land on the retina, by
filtering out the peripheral beams of light. This peripheral filtering reduces unwanted spherical aberration and retinal defocus, leading to an increase in depth of field (i.e., wider range of clear vision).
Many people notice that holding one's arm immediately above eye level would increase visual acuity. Pinhole glasses essentially operate on the same principle - only in a more sophisticated manner.
For people with -2D of myopia or less, reading can be done at a reasonably far distance. Consequently, using pinhole glasses for close work is not necessary. However, for people with higher myopia, reading distance would be too short without minus lens. In such cases, pinhole glasses can be used instead to read at farther distances. Doing so would eliminate minus-lens-induced-near-stress that would otherwise occur.
Although pinhole glasses provide clarity in a relatively safer way, it is still not without its drawbacks. One of its side effects is that it over-restricts peripheral vision, making it unsuitable for activities requiring attention to the entire visual field. Another side effect is the dramatic reduction of incoming light, which then needs to be compensated by increasing background light level.
Since peripheral vision and ambient light are both necessary for normal emmetropization, the continued use of pinhole glasses (e.g., more than 2 hours at a time) is not recommended, as it could trigger
form deprivation myopia.
(No sweat though. The time course of form deprivation myopia differs from that of lens-induced myopia, in that the former would recover as one reverts back to normal visual environment. Form deprivation myopia is only a concern with substantially longer deprivation period (e.g., >24h), in which case the eyes might recover only to a limited extent.)
How do I know if I'm feeling near stress?Here is
Kathi talking about her experience:
I do notice when my eyes get tired form reading and feel pressure behind them when my glasses are on that goes away when I take off my glasses.
Kathi noticed that near stress can be triggered either by close work, or by minus lens. Notice that she talked about pressure
behind her eyes, This symptom is called posterior ocular pressure. In clinical jargon, this corresponds to an increase in vitreous chamber depth.
Here is Alex_Myopic's experience of near stress:
Something that I forgot to mention is that when I was fully prescribed -2,25D and wore them for hours I had a strong feeling at the end of the day to wear them off because of eye strain. I thought it was due to the heavy metal of the frame but even now I wear the same frame and I don't have this feeling, so maybe it was due to the inner eye strain full correction minus provoked.
Here is
Asli Han experiencing near stress, as the result of focusing close for a sustained period of time:
When I use computer without glasses and read-from 25-32cm, usually in half an hour I feel my eyes getting tired
For myopia rehabilitation, should one use bifocal rather than two separate pairs of glasses?Personally, I can't recommend doing that. While using bifocals (with appropriate prescriptions for both near and far) for far activities is not really harmful for low myopes, using such bifocals for near activities amounts to overprescribing oneself. This is because while engaging in near work, the top portion would then induce hyperopic defocus on one's upper retina.
In other words, just because one have learnt which portion of bifocal to use for which activity, doesn't mean that bifocal won't affect them. In fact, countless peripheral-hyperopic-defocus studies, both on human and other animals, invariably suggest otherwise.
Can higher myopes use prescription that only corrects one eye?The approach of correcting only one eye is called
monovision. Why on earth would someone do that you ask? This is because even though the oculars receive images of different levels of clarity, after the transmission of electric signals to the primary visual cortex, the brain integrates the two images into one. As a result, the subject actually gets clear binocular vision.
Monovision is not a bad idea, as it enables clear vision without compounding near stress in the uncorrected/undercorrected eye (as a sidenote, you may have to deal with the resulting double vision on your own, if the disparity between two eyes becomes large). There are studies on monovision that alternates the corrected eye. In fact, monovision studies provide the definitive evidence of the harmful effect of negativizing prescription. Monovision is also a solution for presbyopes, which allows one eye for far vision, and the other for close vision.
What are the pros and cons of using traditional minus spectacle to do work at the far point?Using an undercorrected traditional minus spectacle at one's far point is certainly less harmful than using a full correction, in the sense that the former eliminates central hyperopic defocus which would otherwise occur with the latter. It makes no sense to use a stronger minus prescription, when a weaker prescription can achieve the same task, while creating less near stress.
However, since the posterior retina is not a flat plane, using a traditional minus spectacle, even when reading at the far point, will still overcorrect your eyes in the periphery. This phenomenon of light projecting behind the retina in the periphery, also called
peripheral hyperopic defocus, has been extensively shown to worsen myopia.
In fact, more is true. It turns out that any overcorrection/undercorrection, in any meridian, can have an effect on the eyeball, and that effect tends to manifest only in the region affected. In other words, defocus is
regionally selective.
Therefore, traditional minus spectacle, which is designed simplistically (i.e., imposes defocus uniformly across all meridians), needs to be used with extra caution. One way of mitigating this issue, is by choosing a minus spectacle with extremely small frame, while taking great care to focus beyond one's far point. Smaller frames for minus prescription prevent the periphery from being overcorrected, and so does reading beyond the far point.
Would it be a good idea for higher myopes (e.g., -3D or more) to rehabilitate with plus lens instead and read at a closer distance?While reading slightly beyond one's far point, either with naked eyes or with plus lens, seemingly induces the same amount of defocus. In reality, there is something more at play.
In December 2013, we toyed precisely with the idea of reading at the edge of blur with plus lens at close (i.e., 10cm). While we acknowledged the resulting increase in blur definition and text magnification (as induced by the plus lens), and the resulting clear flashes after each session, it also wasn't long before we observe a worsening of myopia over time. After some more observation and experimentation, we also realized that the worsening was primarily caused by the substantial increase of near stress. A bit more research then revealed proximal accommodation as the main driver of such near stress.
To be a bit more pedantic, proximal accommodation was originally discovered by measuring refraction of subjects who were asked to read through a tiny pinhole - a practice which would eliminate primary optical defocus. Earlier research found that proximal accommodation increases along with the decrease of reading distance, at a rate of approximately -0.2D per diopter of accommodation load - A finding consistent with our daily experience with near stress, which is hardly relieved by the effects of even stronger plus lens.
To further complicate the matter, the effect of proximal accommodation operates in a
regionally-selective manner. This means that reading in a narrow corridor can still induce proximal accommodation in the ocular periphery, and this is even if the corridor measures 6 meters or longer. Without devices to trick us into believing that the objects are coming from far, the only way to relieve proximal accommodation is to read in an environment with a
radius of 1 meter or more.
In practice, this means that while a -3D myope might get away reading at 33cm with naked eyes, higher myopes should, in general, consider using the tools at their disposal (e.g., increased text size, magnifier, pinhole glasses) to read at farther distances (e.g.,1m), while taking active steps to reduce the duration of each near work session.
What are the risks of using thick optical lenses? While optical lenses are designed to be transparent, as the lens thicken, an unintended effect invariably occurs. Namely, the light rays would become significantly diffused by the lens, and non-stop exposure to
diffused blur has been shown, both in animals and by us, to induce form deprivation myopia.
In fact, we were able to replicate form deprivation effects on our own, through the prolonged use of strong minus lenses, strong plus lenses and sunglasses. However, we were also able to recover from form deprivation myopia, provided that these lenses are not used for too long. This is consistent with the findings on the time course of form-deprivation myopia, and the time course of its associated recovery.
In practice, this means that if thick optical lenses are to be used, they should be removed every hour or so to allow the eyes to recover the resulting optical distortions. However, a far more sustainable solution would be to obtain high-index lenses of the same diopter, as the stronger bending power of high-index lenses allows for thinner lenses to be crafted.
For some technical details on form deprivation myopia, see
here.
