We've all seen the startling numbers -- society as a whole is getting more and more myopic with each generation at a speed that can't be explained by genetics alone.
About 1/3 of the US population is near sighted, an increase of 66% since the 1970s, and in Asia the number of school children that are near sighted may be as high as 90%. But with the
World Health Organization now discussing a true myopia epidemic, scientists and researchers are struggling to understand in a very short time why our vision as a population is changing so rapidly. The real truth is that we can only theorize what is causing our eyes to change -- studies on chicks and monkeys about how the eyes develop in different environments give us some insight, but to understand the human eye we often have to rely on correlational study data that can prove cause, only relationships. The result is a number of theories for why myopia occurs and progresses:
Nearpoint Stress Model
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Kids are drawn to visual stimuli like lights and colors, and they
tend to like to get very close! With the near point stress model
of optometry, too much time or strain on the eyes this close
may eventually result in us becoming myopic! It gives credence to
listening to mom and dad about not sitting so close to that TV. via |
The most studied and discussed theory behind why children develop myopia is that it is a result of visual stress from near work. Our eyes are evolutionarily made to excel at distance vision. Images from about 20 feet away would have perfect resolution to details as small as 8.87 mm in size in a "perfect" or normal eye. But today's world finds us even as very young children spending less time looking across the horizon, and more time looking at objects much closer. Think about a book, cell phone, tablet, computer, television. All of these items are much closer than what our eyes are theoretically best designed to see. In order to see things clearly up close, our eyes use the focusing system (which includes the eye muscles and the lens inside the eye, also called accommodation) to bring focus closer in. Our eyes are designed to be able to change this focus back and forth between distance and near until we age to the point that the system no longer works -- this is called presbyopia and it's why people can't see as well to read after age 40. But in a young child, the focusing system is flexible and should be able to transition back and forth to see both up close and far away. The near point stress model of myopia theorizes that if too much time is spent up close, or if for some reason up close work is more difficult than it should be, the eye will begin to change to reduce the amount of stress it has to overcome to focus clearly at near. When the eyes design themselves for easier, clearer reading vision that means they no longer focus light clearly far away -- this is myopia.
Here's the body chemistry behind the model: our body responds to stress by activating the
sympathetic nervous system. You'll often hear this referred to as fight or flight. When our body is stressed by environment or emotion or fatigue, or just about anything difficult or stressful, the sympathetic nervous system takes over. This is the system that increases our heart rate, speeds up breathing, slows down digestion, and makes us more alert. With the eyes, an activation of the sympathetic nervous system means that your pupils dilate so that you can take in more light and be more aware of your surroundings. In order for your pupil to dilate, your ciliary muscle (the muscle around the iris that also controls our focusing system!) relaxes. As a side effect of this muscle relaxation, your focusing system relaxes. Your body has entered an alert mode that was meant to help it see threats from far away --but that means you've just diminished the action of those eye muscles that let you focus on things up close. So the theory here is that when you get stressed (you are learning to read and it's a hard word, you've been reading too long, you're tired), your body enters sympathetic/fight or flight stress mode and your body now makes it even harder for you to see what you are reading! The result of all this stress? Your body has two choices:
Fight (which can lead to common binocular vision issues like convergence disorders, accommodative spasm, and ultimately even the prescription changes that result in myopia)
or Flight (which is what some children do -- they avoid reading, and
may even get incorrectly diagnosed with ADD).
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| Need a refresher? Accommodation is what each eye does to bring the image into focus clearly on the retina. Convergence is the movement of the eyes together to point both eyes at the right place in space for clear focus on the image. These two systems work in conjunction to keep vision clear and single. via |
Let's say your body decides to fight -- what's going on in the eyes when they are fighting to stay focused up close? When we are trying to focus on a near image but our accommodative system isn't able to handle the work to bring the image into focus, our eyes turn to the convergence system. Convergence is the system that brings the eyes together to focus on the same point in space. When we look at something up close, our eye muscles turn in (convergence), and shift focus closer to the object (accommodation).
If you don't have enough accommodation to see clearly, then you draw more effort from the convergence system. If you are over-converging to make up for insufficient accommodation, then your eyes have what's called an
esophoric posture. The problem? If you are overfocusing on a target, that means your eyes are much more likely to see double since they aren't positioned equally to where you are looking. How do the eyes try to prevent from seeing double? They try to pull in more accommodation. This back and forth balance between accommodation and convergence as they work to keep vision clear and single is called the AC/A ratio and one of the foundations of binocular vision system performance. The theory of near point stress implies that accommodation and convergence are constantly out of balance in the patient at risk, and the eye adjusts its shape in order to relieve some of this constant pull and tug by becoming myopic. Image can't focus clearly on the retina? Well let's make that eyeball longer so that when I look up close the image falls on the retina without any effort from this beat up focusing system. But if lengthening the eye is the body's way to solve the problem, why does the myopia keep getting worse? The reason is that the balance of accommodation and convergence is still messed up, so the eye has to keep lengthening to keep things in check.
In this theory, vision therapy may play a role in myopia control. If we can find early children at risk -- children that have accommodation or vergence issues that are just starting to express themselves, then we can help the child develop their focusing system skills to handle the amount of near work required to get through the day at school and home. If your doctor has talked to you about your child needing vision therapy or reading glasses or both, they may have mentioned something to the extent of "wearing glasses now may help keep them from needing glasses later." If so, they are citing this near point stress concept of myopia progression.
Theoretically if nearpoint stress was the sole cause of myopia development, then wouldn't wearing bifocals that reduce the accommodative demand for near work prevent myopia progression? Unfortunately this doesn't hold true in clinical research.
Studies where children were prescribed single vision glasses compared to children prescribed progressive glasses (with a reading power in the bottom to reduce near accommodative demand) report no clinically significant reduction in how quickly myopia progressed. Undercorrecting myopia has also been disproven as a possible means to slow myopia creep. In fact, undercorrecting a child
has been shown to make myopia progress faster than fully correcting the child's prescription! So if near point stress isn't the whole story, what else is causing myopia to develop in our children? In our next post we talk the other two theories of myopia development: sunlight exposure and peripheral defocus theory.
Do you think it might be possible to *reverse* myopia using vision therapy? Apparently some behavioral optometrists have reported success with that.
OdpovedaťOdstrániťCan optometrists usually detect pseudo-myopia, and do they usually check for it before prescribing glasses or contacts? From this post, it seems very plausible that pseudo-myopia and true myopia have a common root cause, in which case reversing pseudo-myopia might prevent true myopia. I talked to a behavioral optometrist, who seems to be widely respected. He said that nearsightedness which has recently developed could usually be reversed by therapy, but once the collagen fibers have stretched (true myopia?), it's too late.
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OdstrániťTheoretically this may be possible if you have "pseudo" myopia -- the patient will present with myopic complaints and accept minus correction on refraction, but they are really just in an accommodative spasm mimicking myopia. Basically the focusing system locks up as it fatigues from near strain and all light entering the eye will get focused in front of the retina, just like what happens in real myopia. Vision therapy is a great treatment for accommodative spasm that would reverse these issues and make the pseudo myopia go away. But as of the current research, vision therapy can't reverse true myopia, which is caused by light focusing in front of the retina due to an eyeball that is too long or a cornea that is too steep.
Your understanding of this topic is perfect! Optometrists check for pseudo myopia by several methods-- adding plus to blur the patient, dilated refractions, checking accommodative ability, just to name a few. The whole crux of the near point model of myopia control discussed in this article is that if you can catch pseudo myopia you can halt it before it becomes true myopia, or if you have already become myopic we can potentially keep that myopia from progressing if it is an accommodative issue that spawned the original problem. The eye will eventually become truly myopic if it is under this level of near stress. A lot of our theories about near point stress and myopia come out of the school of behavioral optometry.
OdstrániťThe comments now appear out of order (perhaps you slightly edited your first response? The time it was posted appears to have changed.) Do you think that most optometrists nowadays actually do check for pseudo-myopia, and inform the patient of the situation? Not too long ago, a regular optometrist told me that the only thing that might have prevented my high myopia would have been hard contact lenses. Also, I actually found this blog through another optometrist's blog, and that optometrist adamantly insisted that any therapy to reverse myopia was a scam (even while acknowledging that at least two optometrists he had studied under believed otherwise!)
OdstrániťYes I had a typo in my first reply but it is fixed now, unfortunately changing the time stamp though. If you had real myopia, your doctor was right-- there is no amount of therapy in the world that can change that. The overwhelming majority of kids that present with distance vision problems have real myopia which means that they aren't candidates for VT as a solution. But we do have ways of screening for pseudo myopia and optometrists test for it at every exam so we can help get those patients the accommodative system therapy they need to help normalize their eye's development. In most people with myopia, this type of therapy won't help because your accommodative system is fine, it's the shape and length of your eyeball that is anomalous and no therapy can fix that.
OdstrániťSo you're saying that pseudo-myopia does not usually precede true myopia? Or that by the time someone gets their distant vision checked, the transition to real myopia has usually occurred already?
OdstrániťYes, pseudo myopia can lead to true myopia if not treated, but not everyone who is a myope started out as an accommodative dysfunction issue/ pseudo-myope as far as the current research tells us. We don't know the exact percentage, but we do know that near point stress model doesn't appear to fully explain myopia's development and progression and there are other issues at play making most of us myopic.
OdstrániťLooking back at my correspondence with the behavioral optometrist, most of what he said seems to line up with what you've said here. He did not use the terms "pseudo-myopia" and "true myopia", but that seems to be essentially what he was referring to. However, he seemed much more optimistic than you do about reversing mild myopia which has recently developed, if the person is motivated to do so. Is it possible that pseudo-myopia, even when it exists, is often not detected by the usual methods? Could there be a stage in between "pseudo" and "real" myopia which is hard to distinguish from the latter? I would ask him more about this, but I've probably used up enough of his time.
OdstrániťIf you know any behavioral optometrists, perhaps you could talk with them about this. This behavioral optometrist said that most optometrists have not been sufficiently educated in the visual system, and thus can't treat myopia as effectively as it could be treated. He said that the most that one could hope to reverse would be about 2 diopters, with the best outcomes tending to occur when the onset was recent, so he at least mostly agrees with your model. Yet he seemed much more optimistic than you do about the prospects for improvement. Interestingly, there are behavioral optometrists who seem even more optimistic about this than he does. Antonia Orfield, a behavioral optometrist who died six years ago, reported having reversed her own myopia by over 3 diopters, as an adult who had been myopic since childhood. Google "Antonia Orfield", "Seeing Space".
OdstrániťAt this point I'm definitely a student of the published research like yourself, and if you are interested in learning more of the science behind the opinions of these different specialists I highly suggest you check out the journal Optometry and Visual Performance (http://www.ovpjournal.org). They have fantastic research in behavioral optometry, vision therapy, and visual development published regularly, and reading this periodical in addition to conferences on the topic has been the driving influence of my current understanding of myopia development.
OdstrániťI think you'll get a lot from this article published in OVP: http://www.ovpjournal.org/uploads/2/3/8/9/23898265/ovp2-4_article_brimer_web.pdf. It sums up nicely a lot of the studies you'll see included throughout this blog too, but this is a great overview in one article of all of the most prominent published studies on myopia and a myopia control by behavioral optometrists.
OdstrániťThanks. I liked this: "Too often, some practitioners feel that they are not obligated to intervene in myopia progression because there is no one clear answer that works for everyone. But it is the optometrist’s responsibility to inform young myopic patients and their families about available options and their potential to slow progression."
OdstrániťMe too! I'm hoping through my own practice and this blog I can help educate more patients and parents about the research on myopia control and that there are things that have been studied and we know can help slow down how fast vision is changing.
OdstrániťIn regards to research which has found no success in reducing "real" myopia: it could be that this kind of thing is very difficult to adequately test. For example, Antonia Orfield reported that her 3.5-diopter improvement took seven years. Let's say it would take several months to reverse mild myopia which had recently developed; the behavioral optometrist I talked to said that the exercises have to be done 2 or 3 times per day for up to 12 months. Not very many people would stick with such a program, when glasses and contacts are available. Even in a study, most of the sessions would presumably be done at home, so how would we know that the subjects really did everything that they were supposed to do? Or that the correct methods were used in the first place? From what I can gather, there is a perception that any therapy to actually reverse myopia has been thoroughly discredited, so researchers aren't interested in investigating that further. But it may be that the studies have more or less been straw-men.
OdstrániťYou could argue that optometrists really are not obligated to inform patients of this particular option, in light of the research. However, if someone wants to try therapy to reverse myopia, it would be far better for them to do it right away, not years later when they're more nearsighted and/or have more responsibilities, and then hear about vision improvement somewhere.
There are several books promoting this, but only a few are by optometrists. One such book is "Take Off Your Glasses and See", written in 1995 by behavioral optometrist Jacob Liberman. I was recently shocked to see a quote from it on the Facebook page of a regular optometrist I had been to, who told me plainly that this was BS. I'm still not sure what happened, but maybe he has changed his views.
I'm definitely not wanting to discourage you from any attempts that you might want to make to treat your own myopia with these doctor's theories, because I don't know anything about your personal case and maybe you are a person whose focusing system is at fault and could benefit from vision therapy. But unfortunately the studies published thus far on reversing true, axial length myopia are very clear that it doesn't work. Maybe one of these other optometrists reporting successes will publish scientific data that will help us change this mindset, and I am all onboard with recommending vision therapy for patients with accommodative and binocular visual system dysfunction at the root of their visual issues. As a doctor I'm ethically and morally obligated to report the real science of vision on this blog so that's the root of the opinions you'll see written here, but we all know that new research is coming all the time, and it may be that we find new data that will change our current scientific understanding of what is and what isn't possible to achieve with vision therapy.
OdstrániťMy local behavioral optometrist seems to agree that axial length myopia cannot be reversed, but from reading between the lines it seems like he believes that there is an intermediate stage between "pseudo" myopia (or what would usually be detected as such), and axial length myopia. I guess if I actually go to him as a patient I will ask about that.
OdstrániťI myself am a true high myope, so it is probably too late for me to reverse it, if it was ever possible.
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OdpovedaťOdstrániťSo in my research/studies you either have true myopia which is not reversible or accommodative spasm/convergence dysfunction which we are calling pseudo myopia here because it can falsely make the patient have complaints of blurry distance. Anytime your doctor tests eye muscle alignment, near reading vision tests, or asks something like "tell me when it gets too hard to see" where they blur your vision on purpose during the glasses prescription check, they are testing for these conditions that might falsely appear initially as myopia. Only the patients that we find have accommodative or vergence system issues might have vision improvements with vision therapy by today's research. So theoretically if you have a normal focusing system, then training your focusing system with strengthening techniques would yield no results on your prescription because you are already normal in those skills. The best way to catch a child who may start as a pseudomyope but progress to true myopia is to make sure every child gets yearly eye exams, even if they don't have vision complaints yet.
OdstrániťThis comment system is pretty messed up. To explain this thread for anyone else who might be reading, I tried to reply in the first thread, but mistakenly started a new thread, and then deleted my comment here and posted it in the correct place. Dr. L's reply is an edit of a comment that was originally in the above thread. Editing one's comment seems to move it to the bottom. I'm not sure if anything can be done, or if that's just the way blogspot now operates.
OdstrániťAs soon as you go to edit a typo or missing word in a post it kicks it out of sequence unfortunately. I suppose blogspot is free after all so we're having to deal with some issues.
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