Eye exercises for myopia prevention and control: comprehensive systematic review

https://www.nature.com/articles/s41433-023-02739-x

by gnabgib • 2 years ago

307 145 2 years ago

billconan• 2 years ago

As someone who grew up in China, we were forced to do this exercises everyday at school. And yet, China has the highest myopia rate.

onemoresoop• 2 years ago

Maybe these exercises help some people but myopia is largely hereditary. It's worth trying though, it's free.

xpe4• 2 years ago

It's worth trying though, it's free.

The above claim strays far from the way of logic. Follow that pattern of thinking, and you'll never run out of things to try.

daveguy• 2 years ago

It's only free if you don't value your own time.

powersnail2• 2 years ago

Maybe these exercises help some people

Similar studies have been conducted in China for multiple times, no clinically significant results were ever found. It probably doesn't help anybody, other than encouraging a short while of not using your eyes.

The guy who first invented the exercise basically just made it up from thin air, trying to fix his own myopia, which was a reasonable effort that didn't work out. But for some reason, it caught on in schools nevertheless.

hosh6• 2 years ago

Turns out, myopia isn't hereditary. It has to do with dopamine interactions and the retina receiving outdoor lighting. When there is insufficient outdoor lighting, the retina starts growing in a different shape, leading to myopia. Just let the kids play outside.

I don't know if going outside more often will reverse it.

Astigmatism, on the other hand, may be hereditary.

yorwba• 2 years ago

Anything that is even slightly hereditary looks "largely hereditary" in the absence of environmental factors. That doesn't mean that large changes in environmental conditions cannot have a large effect on hereditary traits.

Body height is largely hereditary if you can avoid malnutrition. But improved nutrition has led to an increase in average height over time.

It's not improbable that spending ten hours a day indoors to study could have an effect on myopia in children, even if the variation among children who all study for approximately the same duration appears to be explainable by hereditary factors.

colinb• 2 years ago

from the conclusion:

"Overall, the results suggest that eye exercises have limited to no efficacy in preventing or controlling myopia progression. Until robust evidence supports their efficacy, available evidence suggests retiring the eye-exercise policy."

rahimnathwani• 2 years ago

ISTR reading that lack of time outdoors is one of the culprits.

This study wasn't conclusive: https://iovs.arvojournals.org/article.aspx?articleid=2360831

hosh6• 2 years ago

Taiwan had something similar, found it it has to do with outdoor lighting (because many kids in both China and Taiwan stay indoors to study), and started a program to let kids play outside. Along with an early childhood intervention, myopia rates have been dropping.

robwwilliams7• 2 years ago

One would need to control for brightness differences.

Light levels outdoors will generally be much higher. As a result, the pupillary diameter will be smaller (a higher f stop in camera terms) and the depth of field will be much deeper and allow higher spatial frequency “reading” with minimal physiological accommodation.

Anotheroneagain4• 2 years ago

It's poorly grown orbits primarily from lead deficiency possibly also from iron poisoning (which blocks it, as well as several other metals) and the lack of other heavy metals.

pants2• 2 years ago

Sorry, lead deficiency??

rojeee• 2 years ago

I remember teaching in China nearly 20 years ago and all the kids did this. I thought it was so strange. Crazy music would come on between each class, which was the prompt to start “eye exercises”. They all stopped what they were doing and massaged their eyes and forehead for about two minutes. Then got back to doing whatever they were doing. Non-participation was punished.

xpe4• 2 years ago

Given that the Nature research (above) shows that eye exercises don't seem to work, we should focus [1] on what does. Research shows more outdoor time can help with myopia. See https://onlinelibrary.wiley.com/doi/full/10.1111/aos.13403

[1] See [1] what I did there?

tremon• 2 years ago

Why is spending time outdoors not considered an eye exercise?

powersnail2• 2 years ago

The study is about a specific type of eye exercise. The translated English title makes it sounds more general than it is.

jspash• 2 years ago

It's probably similar to the difference between doing "proper" squats in a squat rack vs. using a cheater frame. The muscle movement is more varied and not as linear as doing a single left/right up/down exercise. But that's just a guess.

adrianmonk• 2 years ago

I don't think they know for sure what it is about being outdoors that helps prevent myopia. But it's thought that it might be the bright light. To me, passively taking in bright light wouldn't qualify as an exercise.

calebm• 2 years ago

I recently was required to renew my glasses prescription because the other one was 2 years old (so considered expired). When I got my new prescription, my optometrist said "your vision improved". I have been spending more time outside. I have found that time on the water seems to make my vision improve. I also suspect that walking through forests and experiencing the parallax effect might function as something like a depth perception calibration. It's also worth noting that I do wear glasses, but not all the time - intentionally so I can exercise my eyes.

hosh6• 2 years ago

It's the dopamine interaction of the retina receiving outdoor lighting which changes things.

I don't think this works on astigmatism though.

LorenPechtel3• 2 years ago

While I can see this altering your prescription why should it improve your vision?

3abiton• 2 years ago

Any research on this?

glandium• 2 years ago

Or, if your myopia wasn't too bad and you're in your 40s, that could just be related to presbiopia. That's what seems to have happened to me, and what the ophtalmologist I was seeing when I was a teenager told me might happen.

FreeRadical• 2 years ago

This may be a silly question but were you spending the time outside with or without your glasses on?

LoudFrog• 2 years ago

Let us know when you have 2020 vision again.

napoleoncomplex• 2 years ago

How does wearing sunglasses affect time outside effectiveness? Any research on that?

(Just something I've wondered since sunglasses are super prevalent)

happyopossum• 2 years ago

My understanding is that the benefit of being outdoors is the ability and opportunity to regularly focus on things at a distance that helps, so sunglasses wouldn't factor in.

kyriakos2• 2 years ago

Sunglasses are not just a fashion item they also protect your eye lens from gradual damage from UV. It may be a good compromise in the end.

drjasonharrison2• 2 years ago

The issue isn't brightness, it's distance to what you are looking at and focus on the retina. When your eyes can still bring far objects into focus, they produce a signal that causes your eyes to grow longer. https://newsroom.uw.edu/news-releases/glasses-stop-myopia-ar...

incognito124• 2 years ago

Rarely do the jokes on HN get a chuckle out of me, but you did it!

medstrom• 2 years ago

This is why we hackers need to install Emacs/Vim on an e-reader and use that as our dev environment... outdoors with Bluetooth keyboard every day.

sieste• 2 years ago

This, or you could switch to an outdoors-themed wallpaper.

initplus• 2 years ago

I assumed outdoor time helps because your eyes spend time focusing at a greater distance. Going outside, but only to use a phone/ereader/book is likely not effective.

moneywoes2• 2 years ago

any laptops with a display bright enough for this purpose?

kreyenborgi2• 2 years ago

I want this! I'd love to sit at the beach with something as readable as a Kindle (and preferably a sand-proof keyboard), but with latency fast enough that emacs or vim is usable. Is there anything close to this that I can buy?

matthewdgreen• 2 years ago

23 of 25 studies were in children, and also it didn’t seem to have any effect in people who already have the problem :(

amelius2• 2 years ago

If VR goggles have the image focal point at infinity, does that count too?

Also, what if you wear glasses that move points close by (e.g. your screen) to infinity?

jerlam• 2 years ago

Regarding your second question, that's basically what computer glasses (and reading glasses) do. They basically make things that are close, visually farther away.

For people who can't focus up close anymore (elderly), they move the book visually farther away where the eye can still focus.

When used as computer glasses, you could see the screen without the glasses, but with the glasses they are shifted farther away visually which helps with eye strain.

jeremiahbuckley• 2 years ago

I’ve heard this is important for young kids when eyes are developing. Once the weakness is built in, there’s not much t that can be done.

But I definitely recommend this to people I know with new babies. We do a bad job consciously recognizing the difference between indoor and outdoor light, but they’re orders of magnitude different in actual brightness.

dsego• 2 years ago

I only started understanding the difference after getting into photography.

toss1• 2 years ago

And I we don't really notice that magnitude of difference because our optical system adjusts so well

hiAndrewQuinn• 2 years ago

Time to give your kids headphones, boomboxes, and old-school mp3 players, everyone. Get them outside and dancing in a forest!

Galatians4_16• 2 years ago

I had to equip my reading glasses, then I saw.

Anotheroneagain4• 2 years ago

No. That hypothesis came from the fact that myopia in Australia was much rarer, but that was because they banned lead later than others.

jurassicfoxy• 2 years ago

Does anyone here suffer from double vision? Do exercises help with that?

4gotunameagain• 2 years ago

The 20-20-20 rule[1] can help with diplopia from computer vision syndrome.

Although I would advise to reduce screen time rather than treat just the symptoms that arise because of it.

  [1] https://wiki.endmyopia.org/wiki/20-20-20_rule
  [2] https://en.wikipedia.org/wiki/Computer_vision_syndrome

Eugr• 2 years ago

What helps me is:

1. Taking breaks more often. 2. Using bigger monitor with bigger fonts, so I could sit further away. 3. Using Apple Vision Pro as a monitor replacement as it gives you 4-5 feet focal distance.

The last one lets me work at my computer all day without getting double vision, but it's not very comfortable and you start to feel the weight after 2 hours or less. Plus the friction on putting it on, connecting, etc.

hi-v-rocknroll• 2 years ago

I have monofixation syndrome without amblyopia, discovered only after age 40 when an ophthalmologist who actually knew what they were doing did their job. My understanding is there no durable or neuroplastic adaptation to double vision, amblyopia, or monofixation syndrome after youth because it is permanently wired that way in the ocular-vestibular systems. Corrective eyewear, eye surgery, and/or weaker eye training at early ages may help, but show no evidence of correction in later years. Monofixation syndrome is a neurological adaptation of the brain to minimize the experience of double vision.

humanfromearth9• 2 years ago

Double vision ? Is this when one sees with both eyes simultaneously ? =)

dbcurtis• 2 years ago

I have double vision from strabismus. There are quite a number of eye therapy exercises that you can do to improve the condition. The older you get, the more of it that it takes. I have made improvements, but before I made this discovery and started the therapy I was too far gone and too old to fully cure. But... I can get decent life improvements if I put in the effort.

If you look hard enough you may find an optometrist that specializes in eye therapy for strabismus and similar vision issues. Expect to be the only adult in the waiting room that is not a parent, most patients will be early-grade-school-age kids.

lucb1e3• 2 years ago

I only ever heard about seeing double after some sort of accident. Do you know what causes yours? The sibling comments seem to assume it is from looking at screens for too long, is that it or does that make it worse?

arijo• 2 years ago

As a teenager, my myopia led me to a book promising clear vision through eye exercises alone. My doctor quickly dismissed it as nonsense, insisting only "science" could help.

Fast forward 30 years, and this post reminds me how valuable it is to approach even expert opinions with a healthy dose of skepticism.

It's a funny twist, highlighting that while expertise is valuable, it's crucial to maintain a discerning mind and not blindly accept any claim as absolute truth.

tarentel• 2 years ago

Did you even read it? It clearly says they're ineffective. Your doctor was correct to dismiss it as nonsense.

s1artibartfast• 2 years ago

If the parent poster successfully treated their myopia, they have a n=1 to the contrary and it is the only n that matters for them.

IncreasePosts• 2 years ago

Ironically, OP saw a random thing that seemed like a claim and blindly believed it.

aatd86• 2 years ago

I don't know wvy you're being downvoted. From various experiences, I have had that realization as well.

francisofascii• 2 years ago

Had a conversation yesterday with an optometrist about this. My daughter's myopia jumped from -.75 to -2.0 in a year. Asked about the atropine drops, special contacts, etc. He said the number one thing was to make sure my daughter was outdoors in sunlight. You can read or be on screens, just outdoors. His opinion was mixed on the drops and special contacts. The tricky part is you don't know how bad the myopia would be without interventions. So my child's myopia might be progressing, but maybe would have been even worse if we didn't do the drops or whatever. He also said growth spurts correlate with myopia progression.

avery17• 2 years ago

Theres a brand of glasses for kids that stops the progression of myopia. Posted on HN the other day, cant remember the name. Look it up!

drjasonharrison2• 2 years ago

https://newsroom.uw.edu/news-releases/glasses-stop-myopia-ar...

Nicholas_C2• 2 years ago

Look into ortho-k contact lenses. My siblings all have terrible eyesight but mine is ok around -1.5 and I was the only one who used ortho-k contacts.

kreyenborgi2• 2 years ago

ortho-k might be able to slow down development, but I haven't seen evidence it can reverse it. The NIH in the US claims ortho-k works for slowing down development https://www.nih.gov/news-events/news-releases/multifocal-con...

But on the other hand, the UK NHS guidance https://www.nhs.uk/conditions/short-sightedness/ says that multifocals may help slow the development, while "Some opticians may advise wearing a special lens overnight (orthokeratology). This can help you see better without glasses or contact lenses" (so the UK guidance does not list ortho-k in the list of things that can slow development, only that opticians may advice using it)

abdullahkhalids2• 2 years ago

So, what is important is what sort of exercises are being used. From the paper, the types are

1. 3D visual training combined with ciliary muscle exercise training

2. Massage (point, eye muscle, head and neck, facial massage roller, automated eye massager)

3. Dazhui vibration (looks like acupuncture)

4. Auricular plaster therapy (some sort of acupuncture using magnetic seeds applied to ear)

5. Badminton training

6. Yoga eye therapy

7. Eyesight gymnastics with physical exercise for health maintenance

First of all, it would be reasonable to concentrate on the interventions where there is a plausible causal model. Should 1 and 7, and maybe 6 (depending on what exercises are being done) be looked at more carefully?

Be being a mere physicist cannot read the forest plots in Fig 2, to determine which of the studies had some positive effect. Can someone else do that?

zigzag3123• 2 years ago

I can't seem to find any studies with where significant amount of time are (at least 30 min daily) exercises like a simple focus distance changes. Do they exists?

abdullahkhalids2• 2 years ago

Exactly. If I were to design eye exercises that had some causal effect on either preventing or reducing myopia, it would be very disciplined focus exercises. Likely customized to the person's current myopia level.

I asked a similar question last week, and someone answered [1] with some proposed resources, the first of which looks reasonable. No scientific studies though.

[1] https://news.ycombinator.com/item?id=40516186

inanutshellus• 2 years ago

Since the Nature.com link just basically says "myopia exercises don't work"...

NPR just had a piece talking about a 2-yr study in Sydney that found that spending time outdoors reduces myopia in children and a 15-year-old program in Taiwan to ensure primary school children are sent outdoors more, which has reduced their % of myopia.

Theory is that we change our focus distance regularly when we're outside. ("hey look, a bird!" "i think i'll stare blankly at that tree while I ponder that document" etc)

https://www.npr.org/sections/health-shots/2024/05/13/1250555...

Notably -- I guess -- the study was about children. Maybe adults are screwed. It certainly is easier to get kids outside more if the govt is backing the changes.

molave• 2 years ago

Anecdotally, this worked on for me. It's not a great improvement, but it was noticeable.

gdevenyi• 2 years ago

The theory is not focus distance changes, but high angle high brightness overhead lighting (sun) and sufficient blue light.

lucb1e3• 2 years ago

I've also heard the high brightness during the daytime helps with getting into a good sleep cycle by setting the biological clock to "ok now it is definitely day". Even when sitting close to a window, the light level is typically still something like 1/10th (or less) of what it is outside.

Not that I do any of this; I enjoy reading long articles and writing code until 5am

zigzag3123• 2 years ago

They say "exercises", although most of the studies listed focused on various types of massage.

outdoorsun2• 2 years ago

what is the best time for outdoor activities w.r.t myopia? morning? noon? evening? night? dusk?

brigandish• 2 years ago

According to Dr Goldberg, who I heard on Huberman's podcast[1], morning sunlight so you can get red light. Dusk/twilight also has red light, but I've heard that it's helpful to combat the effect of bright light before sleep, like that from screens, for some reason I forget. Now I make sure to get a bit of both.

[1] https://www.hubermanlab.com/episode/dr-jeffrey-goldberg-how-...

outdoorsun2• 2 years ago

if your doctor put new prescription, do not throw away your old glasses

try these instead. it's free and reproducible.

test on variations: on bright day with sun light (outdoor) focus on a fixed distance, say 4 meter. wear old glasses of -.5, -1, -2 ... and your new prescription keep note which if those glasses give clear vision

then vary the distance to 15cm, 30cm, 1m, 2m ... very far

then vary the brightness level, next go to building with low light intensity, like underground parking

then do the variation on distances and glasses' power

keep notes of all your experiments

the idea borrows from design of experiment of 2^3 factorial design: high and low brightness short and long distances old and new glasses

the conclusion would be use the least power for different situations and best if you dont use any glasses (well, there's plus lens therapy which is the next step)

say if you can see clearly thing on your phone (15 cm, light emiting screen -- i always use max brightness) without glasses, the don't use glasses

if your -1 glasses are sufficient for desktop work, don't use higher power although no glasses wont hurt (i increase the font size till legible)

anyway, if you're determined to do the experiments, please let us know

thank you in advance

komodus• 2 years ago

I remember my eyesight was 20/20 all my life until I started playing more and more with phones and tablets, now I can barely see any font in a regular browser tab at 100% zoom so I set it to 150% by default.

One thing that changed for good is using a 50" TV as monitor connected to my mac mini at 4' distance from my chair. Now my eyes don't cross anymore and my sight has improved a lot.

So yes, I concur that looking at clouds and the horizon everyday may be a good way to recalibrate our eyes. Spend more time outdoors.

[edit] Oh, and whenever I can, I cast my phone to my tv in the bedroom so I don't spend countless hours on tiktok forcing my eyes. I wish tiktok and instagram were available in landscape mode.

ein0p• 2 years ago

If you have an iPhone, it can warn you if you’re holding it too close if you enable the warning. Turns out I do that a lot, without realizing

pyaamb• 2 years ago

One time during a long screen time session I happened to notice by accident that looking at the reflection of the screen in the office window produced almost no eye strain even though I could comfortably make out all the text off the screens reflection. Made a mental note to research into this for a potential solution but never got around to it. Find myself imagining if some setup based around a semi-transparent screen which absorbs/reflects away just the right amount, combined with a mirror to simulate long distance could be worth experimenting with for someone sufficiently motivated. Think of the setup in the opticians office where you read letters off a mirror, but semi transparent. Has anyone seen anything akin to this?

User232• 2 years ago

Every other body system—pulmonary, circulatory, nervous, skeletal, and muscular, just to name a few, shows marked long term physical changes, called adaptations, to stresses. See Selye for the basics.

Why would the optic system be any different? We know beyond a reasonable doubt that myopia is a kind of environmental maladaption. The only question is what stressors cause it and which can act as training stimuli to mitigate or reverse it.

That’s not to say that training stimulus will look like exercises. I don’t really know what it will look like. I do know however that my own myopia stopped progressing when I stopped letting my optometrist change my prescription.

I would not be at all surprised if the standard of care is actively harmful and significantly contributing to the skyrocketing myopia rates. But good luck funding that study or getting enough optometrists to go along with demonstrating their entire field has been screwing up for a century.

RoyalHenOil4• 2 years ago

Exposure to bright light is the key factor. It is especially important during childhood, when the eyes are still growing and developing.

Once elongation of the eyeballs sets in during childhood and the teen years, there is generally very little (if anything) that can be done about it in adulthood. Adults' eyes do not change shape very much after a certain age.

So-called "eye exercises" of the future will probably look something like having children look at bright lights or spend time outside in sunlight for some period of time each day.

elango• 2 years ago

Tooth decay and Myopia have industries built behind them, there is no motivation to fix them.

Der_Einzige• 2 years ago

Can someone explain the strong casual relationship between myopia and high IQ?

This is just one of the many studies which have shown this relationship: https://pubmed.ncbi.nlm.nih.gov/19127804/ and https://www.ajmc.com/view/nearsightedness-correlates-with-hi...

Seems to validate all of the stupid lore of "four eyes" being objectively on average more nerdy and smarter.

Seems time spent outside trades off with time spent sharpening the mind in the way that benefits IQ tests - do I want my kid to be a nerd or a jock?

nottorp• 2 years ago

Maybe for minor IQ improvements. Because if said kid actually has a high IQ they'll learn faster and have time for both outdoors and indoors activities.

RoyalHenOil4• 2 years ago

Correlation is not causation.

There are many ways that these two traits could become correlated. For example, poverty is associated with both poor childhood nutrition (which is possibly the biggest cause of low IQ) and with more outdoor activities (due to more unskilled physical labor, more rural living, fewer electronics at home to keep kids entertained indoors, etc.).

barbariangrunge• 2 years ago

I’ve improved my night vision (headlights on the highway at night kind of thing) with some exercises I made up. I think shifting from light to dark focus uses muscles and those muscles can just get weak. You can just exercise them and they get better at adjusting

Cold_Miserable• 2 years ago

Even a thicko can figure out this "research". You can't exercise your eyes to change their physical shape.

noobermin• 2 years ago

This is a welcome study indeed. Eye exercises always seemed like grift, often being promoted by types who hawk other kinds of grift cures and mindfulness techniques. Now here is actual evidence.

tluyben2• 2 years ago

These were some of the first 'self help' books that were sold by internet 'marketers'. Most of them you could find for free, but they would charge a few $ for them and 'cure your eyesight'. Never knew that could actually work because of that.

Anotheroneagain4• 2 years ago

It can't work, because myopia is caused by poorly grown orbits. Take a careful look, and you can tell who is myopic, and who isn't, with fairly reasonable accuracy. Or, perhaps try training AI to tell the difference, to remove any bias for it.

simonebrunozzi• 2 years ago

Talking about Myopia - I have it (~2 and ~3 degrees, so not particularly bad), I am in my mid 40s, and I have been considering a surgery to fix it. Let's assume that for this particular case, money is not an issue.

There's a ton of different types of surgery available [0] to fix refractive errors.

Besides Lasik, which I think is the most popular but not necessarily the best, there's at least two other options out there:

1) Photorefractive keratectomy (PRK) - 1st gen

2) Laser-assisted stromal in situ keratomileuses (LASIK) - 2nd gen

3) Small incision lenticule extraction (SMILE) - 3rd gen

However, I am not fully convinced that SMILE is absolutely by far the best; and it's not easy to find the right provider (outside the US).

Anyone with experience or knowledge that could help navigate this mess?

[0] https://www.urmc.rochester.edu/encyclopedia/content.aspx?con...

spoiler• 2 years ago

Similar, boat but in my thirties. I talked to a ophthalmologist and eye surgeon (friend's mum) and to people who sold me my glasses.

Both said it doesn't matter too much which method it is. Just pick a good/reputable clinic and go have a conversation with them. They'll recommend the treatment they think is best for you.

jamesralph8555• 2 years ago

I would recommend finding a good (modern/updated) treatment center near you that at least offers LASIK and PRK, then get a consultation. They will perform tests on your eyes and let you know which procedures will work for you. Due to factors like corneal shape and thickness, you might not be eligible for LASIK which at least makes the decision simpler. From what I’ve read, outcomes are very similar between the 3 types of surgeries. I ended up going with LASIK since you can get back to work in a few days instead of a week with PRK.

meristohm• 2 years ago

I started noticing a drop in visual acuity about a year ago. The LCD clock on the stove was blurry from across the room.

After listening to this podcast episode

Building Better Vision - Jake Steiner #96 REWILD YOURSELF JUN 29, 2016 ⋅ 1:29:41

I started wearing my reading glasses for all nearby work, going outside more often, looking further away rather than a short distance ahead while walking, and generally trying to reduce eye strain. I have not yet read Steiner's blog, which he urges for a more complete understanding. I also stopped playing games on my Steam Deck screen, opting for an external monitor to increase the focal length and thus reduce strain.

Anecdotally, things don't look so blurry now, and the stove LCD clock is easier to read.

snozolli• 2 years ago

started wearing my reading glasses for all nearby work

Here's a study summary on giving student pilots reading glasses to prevent myopia from reading all the training material:

https://pubmed.ncbi.nlm.nih.gov/31080964/

Off the top of my head, from reading about this a few months ago, I think it's mostly a critical period as a child to young adult where this has the most effect.

Some opthalmologists invented glasses for children that reduce the worsening of myopia:

https://newsroom.uw.edu/news-releases/glasses-stop-myopia-ar...

Again, off the top of my head, the eye is stimulated to grow longer by dopamine, and the dopamine release is influenced by the focus difference between what's at the center of the eye versus what's at the edge. Somehow, those glasses reduce that effect, so the eye doesn't continue to lengthen past farsightedness and into nearsightedness.

meyum33• 2 years ago

It seems this is a mainland China study. “Eye exercises” here has a particular form, which is called 眼保健操. IIRC it was developed during the cultural revolution based on traditional Chinese medicine. In short, the conclusion is that this particular exercise doesn’t work, not that exercises for eyes in general don’t work.

seesawtron• 2 years ago

Is it just me or do you also see half of the article in Chinese when clicking the above link?

Eye exercises for myopia prevention and control: comprehensive systematic review

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