Myopia - How Did This Happen?
[!info] This is the third in a series of posts about the epidemic of myopia (nearsightedness), my personal experience with it, and what people are doing about it. The second part is *"Myopia - So What?"
So far I've tried to show what the problem is with nearsightedness, why it's not harmless, and why it's not just genetic. Before talking more about my own experiences with it, it's worth talking about how we got here. We could ask this question in two senses:
- How did eyecare professionals take the erroneous stances for so long that this disorder was solely genetic, there was nothing to do about it, and that it could not continue to get worse after adolescence?
- What factors or by what means might an eyeball actually get too long?
For the first question - I'm not sure I'm equipped to address that yet. I haven't looked into the history of the profession much. I did have an optometrist tell me at one point that many ophthalmologists likely don't update their opinions much after their education, which would mean transmission of new information is very slow. There also could be confusion between the different types of practitioner - optometrist and ophthalmologist. The scope of optometry seems to be expanding, but the fields still seem like they talk at odds with each other sometimes. For example, an ophthalmologist's nurse will try to assess someone's eyeglasses prescription and prescribe them eyeglasses. But vanishingly few of them seem ready to prescribe specialty lenses for myopia control, a set of myopia treatment methods we'll discuss in a while. Still, this might be changing - a post on a professional academy website acknowledges as of 2020 that myopia is an issue and there are treatments available However even as of 2020, the article seems to be a bit behind on mention of treatments.
Some of this may also be due to the strange economics of various health systems and professions.
In any case, I suspect there may be some reckoning for practitioners themselves, and within the eyecare field as a whole, as more evidence emerges to contradict conventional assumptions.
As to the second sense of the question, let's get into that.
hypotheses for what's actually going wrong
peripheral defocus theory
This was pioneered by, among others, the University of Houston researcher Earl Smith III. As I understand it, the idea is roughly that with standard spectacle correction, the image projected toward the retina would actually be cast too far beyond the outer edges of the retina, which triggers signaling in the eye that provoke it to expand. Another example of where it's discussed at a high level found here.
These graphics from the lens manufacturer VTi attempt to illustrate the idea:
accommodation issues
Acommodation relates to parts of the eye's ability to alter to change its focus for near or distance focus. There is research being done into whether these mechanisms are impaired in myopic people or altered by standard spectacle correction. I don't understand all of the technical details or vocabulary, but recent example of this is mentioned here and also discussed here
schematic showing acommodation concepts
intraocular pressure and biomechanical issues
Another source of the problem being investigate relates to how much pressure is in the eye, the intraocular pressure. This is often disregulated in glaucoma patients, and highly myopic people are also known to have higher rates of glaucoma. A rough analogy to this line of investigation might be to think of the myopic eye like an oblong water balloon which is stretched and weakened on one end. The hypothesis being that if there's more pressure from the fluid on the inside, the weak portion may expand more. This may relate more to highly myopic adults than children, and I believe this is a newer line of investigation. For examples, it is mentioned here, and also here.
tonometer, a device used to measure eye pressure, when not using the dreaded "air puff"
dopamine disregulation
This one is a bit more complex, perhaps a newer line of investigation, and I am less familiar with it, but the idea is that dopamine is disregulated as summarized in this review: "In conclusion, these findings collectively suggest that the interaction between dopamine, melatonin, melanopsin, and ipRGCs and ocular growth regulation represents a complex system that demands continued scientific investigation."
It can be found in scholarly articles like this one.
It is also the basis for a newer device, but which has less of an evidence base for its effectiveness: https://dopavision.com/
This device deserves special consideration and in my layman's opinion a heavy degree of skepticism, because the device actually relies on blue light, which is also under research as a cause of myopia progression (mentioned below).
dopamine molecule
blue light
I was told by one practitioner that myopia is caused by blue light. No other potential causes were mentioned, implying that practitioner believed blue light was the sole cause. I am not convinced that this practitioner has as much expertise in this area as in certain other areas where they had gained patents etc. However, there is evidence that blue light may cause or exacerbate axial eye elongation, such as described here
blue LED lights
Vitamin D issues
There has been some evidence that lower levels of Vitamin D were associated with more eye elongation, though as described here, that may be an indirect correlation relating to time outdoors. More outdoors time is associated with both higher levels of vitamin D from sun exposure as well as having a preventative effect for myopia progression in children.
wikipedia diagram of vitamin D absorption from sunlight
contrast sensitivity problems
This is a rather distinctive approach that is mainly addressed by SightGlass Vision, founded by a husband and wife research team from University of Washington. As the company website says: Artificially high levels of contrast on the retina signal the eye to elongate. Our modern urban lifestyles come with artificial contrast (reading, using electronic screens...).
source: sightglass vision
I've alluded to my own experience with myopia. I'll take a moment in the next part to be more specific.