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The Case for Transmissible Alzheimer's Grows (blogs.scientificamerican.com)
341 points by pseudolus 9 days ago | hide | past | web | 130 comments | favorite





An increase in amyloids will be observed any time cells are malfunctioning for whatever reason.

They are the most thermodynamically stable structure that polypeptides can form, and require constant housekeeping to prevent. Accumulation of amyloids is like failing to taking out the trash in your house.

Afaik, there has never been a disease state checked for amyloids that failed to be associated with them (heart disease, cancer, stroke, etc).

>"From a wide range of in vitro experiments on peptides and proteins we now know that the formation of amyloid structures is not a rare phenomenon associated with a small number of diseases but rather that it reflects a well-defined structural form of the protein that is an alternative to the native state — a form that may in principle be adopted by many, if not all, polypeptide sequences

[...]

These observations, therefore, have led to the remarkable conclusion that, at the concentrations present in living systems, the native states may not always represent the absolute free energy minima of the corresponding polypeptide chains — the native form of a protein could in some cases simply be a metastable monomeric (or functionally oligomeric) state that is separated from its polymeric amyloid form by high kinetic barriers" http://www.ncbi.nlm.nih.gov/pubmed/24854788

I've previously commented the same thing:

https://news.ycombinator.com/item?id=14914528#14917057

https://hn.algolia.com/?query=amyloid%20nonbel&sort=byPopula...


That's fascinating! I wonder if we could ever get to a point where people regularly can check their amyloid levels to see if they are becoming ill

Not a bad idea in principle.

In practice you have to figure out a way to detect them non-destructively (eg via light interacting with it in the tissue or some metabolite in excretions).


Please keep mentioning this stuff. It's shocking how poorly informed the average scientist is about this topic.

I plan to. I was similarly ignorant until I looked into the topic of natively unfolded peptides for a different reason (anomalous western blot results).

If you have any examples of these "uninformed scientists" on display it may be helpful to others. The purpose is not to point fingers, but to see where things may have gone wrong.


Is it fair to infer based on this that they are a symptom and not a cause? Or at least, not a primary cause, though their presence may crate a feedback loop?

I would think it is a good idea to assume they are a symptom but could also cause further problems.

Just like sneezing/coughing does occur normally, but is also a symptom of many different health issues, and in the worst cases could lead to broken ribs, etc.


Could amyloids be a proxy for aging in general? And systems declining in their ability to remove amyloids the cause of aging?

Or a symptom of aging. As for a proxy I doubt it would be much better than actual age.

Does this line of inquiry mesh at all with the idea that "Gum disease–causing bacteria could spur Alzheimer’s"

Or are they competing hypotheses?

reported here in January: https://news.ycombinator.com/item?id=18987015


My wife‘s grandmother had all her teeth pulled and replaced with implants (probably a hint towards lifelong gum issues, and PERHAPS stirring/aggravating infections), and 2 years later developed aggressive Alzheimer’s, dying about 3 years later. She was only 64 when she died. To my knowledge, she never had any neuro or eye surgery. It’s just n=1 of course, but to me the gum disease hypothesis looks way more promising.

My relatives who had/have Alzheimer's haven't had any /reported/ gum disease [so I'm not ruling it out].

Age when teeth are pulled probably correlates well with age when Alzheimer's is first noticed.

It's like "newspapers cause cigarette addiction, people always buy cigarettes in stores where they sell newspapers" [apparent correlation; insufficient observation].


Or perhaps infection by prions by metal dental equipment.

Unlikely because only eye and neuro tissue would carry prions for contamination of equipment, right? Dental equipment should never come in contact with such tissue.

https://news.ycombinator.com/item?id=18648043

There was another HN thread about the "indestructibility" of prions, and I believe there is a growing consensus that they are not removed by existing techniques within dentistry.


Aren’t gums chock full of nervous tissues?

Oh yes, you are right. I hope this whole issue will trigger some research. With these massive costs for Alzheimer's treatment coming towards them, even insurances should be interested in real advancements by now.

The upper palate has a direct line into the brain to facilitate smelling neurons. It is conceivable that a surgical operation on the upper teeth might cross contaminate patients.

Your hypothesis doesn’t make much sense to me. Why wouldn’t you assume that something about the surgery caused Alzheimer’s since that is what directly preceded its onset?

I think it's not the surgery, it's that the surgery was required due to gum disease

Right - I understand that. I'm asking why you would assume that gum disease caused Alzheimer's since it appears that CURING it directly preceded the Alzheimer's.

We had a family member have all their teeth pulled and go with dentures/implants and it seems to have triggered aggressive Alzheimers as well.

What evidence do you have to support that hypothesis?

Could be correlated if it is transmissible. Gum disease could be an access vector for prions into the nerve system and the brain.

well, Alzheimer's has been highly correlated with diabetes (which diabetes is correlated with gum disease), so its hard to tell. If I were to guess, given if there is a correlation with gum disease and Alzheimer's, I would bet my money that what ever causes gum disease also causes at least some Alzheimer's - not that being treated for gum disease causes it.

Diabetes 1 or 2?

If #2 then I'd venture to say that in many / most cases that correlates with abuse of sweets (read: sugar) which would all effect the teeth (and perhaps in turn the gums).

It's unlikely that simple. That said , I'd venture to say aggregate increase in sugar consumption correlates to increases in Alzheimer's. Yes, as do plenty of other mod cons.


My concern is that having general high amounts of inflammation in your body alone increases your risk for Alzheimer's. As someone with inflammation diseases galore (including gum disease), I hope I'm just making inferences where there's no data to support them. Anyone know if that's the case?

And related, does all of this mean that it is a good time for research into the causes of Alzheimer's because of lots of promising ideas, or a bad time, because there's no consensus?

I think some of it may be communication of "mental illness".

Just a clarifying point from the article: Transmissible != Communicable. Still, it makes me wonder what sort of other spooky “life forms” we can host.

1. If certain Prion disease(like say CJD) was Communicable with a high R0[1] by say contact, fecal matter, saliva we would see a lot of people dying, since CJD has a mortality rate of 90% within 1 year[2].

2. The level of A-beta protein(i.e. not technically prion just yet) again the deposits in 7 of the 8 patients was so severe that if this were communicable easily with a high R0, it would also be seen in the general population by now.

So one does not need to worry at least about communicability of this through those means just yet. But transmission if postulated experimentally through certain means like say dental health can mean that we might be able to put a dent in a health crisis of a greying population.

[1] https://en.wikipedia.org/wiki/Basic_reproduction_number [2]https://en.wikipedia.org/wiki/Creutzfeldt%E2%80%93Jakob_dise...


1. CJD is only one specific instance of Prion disease. Others (e.g. vCJD) have incubation periods of - multiple decades -. From the article: "In the original Alzheimer’s transmissibility study, scientists examined the brains of eight patients treated with prion-contaminated human growth hormone as children who decades later died from prion disease"

Alzheimers is growing at epidemic proportions, globally [1].

Alzheimers in the US is growing at alarming rates [2].

[1] https://www.alzheimers.net/alzheimers-is-on-the-rise-in-thes...

[2] https://www.alz.org/alzheimers-dementia/facts-figures


  Alzheimers in the US is growing at alarming rates
Is occurrence increasing alarmingly, or is it just being more properly diagnosed? "Senility" and "old age" may not have been properly isolated last century.

I do wish those numbers controlled for population size, and rates of known correlated variables (e.g. diabetes).

What I want to know is whether the probability of developing the disease given I am a X year old healthy male/female has increased.


The article mentions that explicitly though [0]

It also doesn’t mean it’s not communicable or contagious, it means we don’t know because it seems no one have looked yet [1]

[0] It is important – imperative – to emphasize that transmissible does not equal contagious. There is absolutely no evidence that people with dementia can spread their disease casually to people around them.

[1] Since Alzheimer’s Disease is so common, and we have not (to my knowledge) been looking for Alzheimer's caused by surgical or other medical procedures that access eye or neural tissue -- particularly in patients for whom the appearance of Alzheimer’s would not be surprising -- is it possible that we are underestimating the transmission potential of this disease, and that such events are less rare than we would guess?


(1) thanks for clarifying, that's a relief. (2) what does transmissible mean, then?

As far as I can tell, the two words mean the same thing. The other commenter may have meant to contrast with “contagious,” which means that it’s not just possible but reasonably easy to transmit the disease. From the article:

“It is important – imperative – to emphasize that transmissible does not equal contagious. There is absolutely no evidence that people with dementia can spread their disease casually to people around them. Even donated blood appears to be safe, as no association with blood transfusions and Alzheimer’s Disease has ever been detected.”


Could be wrong but communicable means you can infect other people around you. Transmissible means the disease does generalize to some extent and is caused by something replicable. That is, if they take some of the prions infecting you and inject it into someone else, it can infect someone else. Broken arms and bad genes aren’t transmissible. Lots of cancers aren’t either (meaning I can’t inject you with my cancer and infect you)

This isn’t especially surprising. It’s about on par with Alzheimer’s being caused by a microorganism. If we accept that this is true, then it follows that Alzheimer’s, as a symptom, can be transmitted. But unless there is a noteworthy vector of transmission, there’s nothing to worry about.

Speculation about eye care equipment sounds like sensationalism until tested.


Not the same terms per se, but if you are one there is a massively greater chance that you might be the other too. This is an area where we should perhaps be wary.

If evidence of transmission between people comes forward, the sociological implications will mean decades of debate. Im not going to fault anyone for taking a keen interest in this area. They are opening a pandora's box.


> Just a clarifying point from the article: Transmissible != Communicable

That's a good point for those who just skip straight to the comments, but you should edit this to use the language of the article (contagious vs communicable)


Dumb question (Wikipedia was of no help), if amyloid beta looks and acts like a prion, why isn't it classified as a prion?

Amyloid-Beta is a specific instance of amyloids, while prions are a class of amyloids:

>"Some amyloid proteins are infectious; these are called prions in which the infectious form can act as a template to convert other non-infectious proteins into infectious form." https://en.wikipedia.org/wiki/Amyloid

So if amyloid-beta is determined to be "infectious" (however that is done) then it would be put in the prion subclass of amyloids.


There is a huge misconception about what is meant by the word "prion". Get this... there is only one (1) prion protein! All mammalian prion diseases are directly related to the PRNP gene. People talk about Mad Cow, Kuru, Creutzfeldt-Jacobs, Chronic Wasting Disease, Scrapie, and a dozen other diseases like they are not all manifestations of the same underlying problem with PRNP gene variants. People talk about "prions" as a general category of proteins capable of causing chain reaction misfolding... which is indeed what happens with PRNP variants, but not a whole bunch of different proteins -- just those transcribed from PRNP (the prion protein gene). We will probably discover that other proteins do this to some extent, but it'd still be weird to call it "a prion" because it's not a proten encoded by the prion gene. Does that make sense?

You don't share any links, but how would you reconcile this with the claims that amyloids are widespread. I posted about it here: https://news.ycombinator.com/item?id=19129157

Is it really the case that PRNP (https://en.wikipedia.org/wiki/PRNP) is the only known amyloid to be infectious?


My comment wasn't so much on the biology, or whether other proteins could display 'prion-like' behavior; it was more so to clarify what I think is a misuse/misunderstanding of the word 'prion'. I say this as someone who perpetuated this misuse until a few months ago, after reading an article about 'prions' in the retina, and spent half the day trying to figure out what the prion protein was, only to discover there was a gene that encoded PRioN Protein (PRNP); that is, we have a specific protein called 'prion protein' PrP. So to ask whether something is a prion suggests a misconception, since that's like asking "is insulin a keratin?" or "is melanopsin an actin?", and the answer would be, of course not, since those are all names of different proteins. Now, asking whether some protein X has properties similar to PrP is a totally legit question (i.e. "is X prion-like?" = great question; "is X a prion" = probably a misconception).

Thanks. It is also not clear to me after a quick search whether any amyloid has been called "infectious" other than ones derived from the PRNP sequence. It is very interesting.

I'm telling you-- i went down the prion rabbit hole myself recently and the entire path is littered with misconception and inconsistencies in how the term "prion" is being used.

One place to start other than wikipedia is this cdc site that lists know prion diseases...

https://www.cdc.gov/prions/index.html

After some digging, I concluded that all the diseases they listed are related to PRNP. Please, please, correct me if I'm wrong.

I'm actually going to chat with a friend in a few minutes who is a postdoc at MIT studying protein (mis)folding, and said he could help clarify. (i'll relay any new insights...)


You seem to be mixing terms a bit, so at risk of repeating things you know, I will explain what I am reading from what you've linked.

PRNP is the gene encoding for "the major prion protein." Several different errors in PRNP create versions of "the major prion protein" that can be folded in a way that is bad (the prion folding). However, that is not the only way in which the proteins can fold themselves.

When lots of these proteins stuck together in an 'amyloid' (starch-like) aggregation, a misfolded (bad) shape of the protein serves as a template, folding more and more instances of the protein into the bad shape.

We consider the shape to be 'bad' because it is associated with visible symptoms of disease.

It is the prion ('bad') folding of a protein which would be infectious.

There are lots of different proteins that create amyloids, but so far all symptoms of prion-type disease for which a cause has been found have turned out to be associated with errors in PRNP.


>"so far all symptoms of prion-type disease for which a cause has been found have turned out to be associated with errors in PRNP."

Thanks, this is an interesting new fact to me if true. Is there a source for it?

I don't mean a source proving there are no others or something else silly like that. I mean like a review article that mentions they couldn't find any publication about any amyloid beyond PRNP-derived ones being transmitted.


I can't give you a source like that. From the Wikipedia article on prions, it appears that several prion-based diseases are suspected, but that so far the only proven cause for such a disease has been the "major prion protein." In 2015 a hypothesis was advanced that multiple system atrophy (Shy–Drager syndrome) was caused by a prion form of the alpha-synuclein molecule. However, if any subsequent proof has followed, neither the wikipedia pages on prions or alpha-synuclein have caught up with that.

It does seem like Abeta and prions should be in the same class.

A possible practical reason to keep them separated would be to avoid having various safety committees at X research institution from adding dozens of barriers to already difficult Alzheimer's research. Doing work with prions is a little like doing B. anthracis (Anthrax) research in some places - having to deal with indestructible spores.

Not that those safety measures shouldn't be put in place, but it'd make Alzheimer's/Abeta research slower and more expensive. The jump from BSL-1 to BSL2+/BSL-3 is huge [0].

[0] https://blink.ucsd.edu/safety/research-lab/biosafety/contain...


This is what the author was wondering at the end of the article. The discovery blurs the line between the two. There is now the question if they may be the same thing.

Article:

What is the difference between amyloid and prions? Are they part of a spectrum? Are they one in the same? If not, what is the difference? Can what we’ve learned about the biology of prions help our efforts to fight amyloid dementias?


Another dumb question: If Amyloid beta is a prion, why is it so common for Alzheimer's to occur only later in life, while teenagers can suffer from BSE? Does it have a longer incubation period?

I think it's true that neurosurgeons have a higher rate of Alzheimer's than the population. This always bothered me.

Even when controlled for factors like being richer than the general population and therefore more likely to grow old?

Source?


I read the abstract (but not the whole article), but how does neurosurgery mortality compare with other employed rich people?

That is, I'd expect cases of Alzheimer deaths to be higher in the wealthy just because I'd expect they would live longer and not die of other ailments before Alzheimer's "got them".


Is it possible that neurosurgeons don't actually have a higher rate of Alzheimer's Disease, but just get correctly diagnosed more often than the general population? I suspect a lot of poor people with limited access to health care die of that disease but it never gets labeled or recorded. But neurosurgeons can recognize their own symptoms and generally have access to the best possible care.

The only way to be sure would be to perform detailed autopsies on a large random sample of the population.


The problem with that theory is that they get diagnosed at a higher rate than other types of surgeons. This would indicate that their direct exposure to something related to the neuro part of their job title is involved.

A possible explanation could be based on research suggesting that regular lack of deep sleep increases risk of Alzheimer’s. Given that Neurosurgeons have a grueling 7-8? year residency period after medical school, it would be possible that they undersleep far more than the control group.

I would like to see how the prevalence of Alzheimer's among Neurosurgeons compares against a population with similar work/sleep schedules (eg. finance)


Do they ever stop? What does a surgeon do in their free time?

From cursory googling it looks common for programs to expect you to work right up to the legal limit (80 hours/week based on 4-week averages) during residency. Having 16 hour days for ~7-8 years means that you probably have to get used to being a bit sleep deprived all the time.

I went to a talk recently [1] in which the researcher explained a theory of the origin of life where early cell membranes were based on amyloids. The theory can be described as ocean vent metabolism and amino-acid first (as opposed to tide pool and radiation/lightning RNA) and it's definitely not the most accepted theory but it's pretty interesting. Here's an open paper [2] and the speaker's homepage [3]

[1] https://www.eventbrite.com/e/ieee-buenaventura-embs-talk-fig...

[2] https://biologydirect.biomedcentral.com/articles/10.1186/174...

[3] https://science.jpl.nasa.gov/people/Russell/


> "In the original Alzheimer’s transmissibility study, scientists examined the brains of eight patients treated with prion-contaminated human growth hormone as children who decades later died from prion disease (out of over 30,000 people so treated, more than 200 died this way). "

does anyone have any clarification on this? to me that is very alarming. that's about .67% which sounds small, but its int he ball bark of catching HIV after having unprotected intercourse (depending on a lot of factors)


How does that compare to control? 200 : 30k sounds like it's lower than normal "infection" rate?

One of the less highlighted shocks here is that sterilization is not perfect.

When even bleach doesn’t work, you’re gonna have a bad time.

It is, for bacteria and viruses. Prions are neither.

I'm starting to doubt the prion hypothesis now that we know amyloid-beta encapsulates viral particles in the brain. I think its more likely that viral infections are the transmitted agent.


(In response to comments about eye care tools being contaminated)

What’s preventing someone from testing 20 optometrists’ tools for prions and settling this?


If prions stick to surgical instruments “like glue” what about needles and lancets? Could this be the link between diabetes and Alzheimer’s?

No. Those are disposable, not sterilized. There’s no chain of transmission.

They could become contaminated during production.

If prions stick to surgical instruments "like glue" how do they come off when used for surgery in the second human being infected? (And can we use that mechanism to get them off to sterilize them?)

Could you wash the instruments in proteas?

Seems BACE2 might be promising.


Those are all one time use though, right?

Apparently lots of diabetics reuse lancets (thread on another HN story a day or two ago). But I can't imagine anyone sharing used lancets (or needles... except for desperate addicts).

Would be interesting to see the rate of Alzheimer's among addicts and former addicts. But I imagine the sets "IV drug users who share needles" and "people who live to be old enough to be at risk for dementia" don't really intersect in any meaningful way.

Can confirm, am diabetic T1. Lancets don’t get changed much on my meter, but if anybody is curious I have a whole separate glucose meter/lancer device and brand new lancets to use.

Sure do. But yeah, no sharing. Never.

Is this thought experiment how antivaxx happens?

Careful thought is the _opposite_ of how antivax happens.

Only if you take the result of the thought experiment as absolute truth and skip the part where you’re supposed to confirm it with a real experiment.

If you have a couple spare hours give Vaxxed a watch. It'll help clarify how such a movement happens.

Would be interesting to find out if increases in the frequency of other neurologic diseases could be prion-related. Autism, for one.

Great. Another reason to regret my lasik.

What other reasons do you have?

Dreading needing reading glasses. Night vision subjectively feels worse. Random yellow spots in changing light conditions that I don’t remember having before.

Forgive me; isn't Lasik all via laser though?

Isn't this more like - you share binoculars with someone and your eye fluids mix (if you both push them too close)?


The steps of fixing your eyeballs in place and peeling back the cut-out flap require physical contact with tools.

But those are all tools that interface with the anterior cornea part of the eye.

Is it correct to assume that the type of contact that would be a risk in this case, is with posterior vitreo retinal surgery where you might have contact with the optical nerve tissue?


Ok thank you, I didn't know.

What about the Alzehemiers link to HPV virus that formes plaques in the brain? How is that related to transmitable peptiods?

What is it with the cell membranes size of these viruses that can travel up and form plaques in the brain?

Alzhemiers hpv link sciencedaily.com/releases/2008/12/081207134109.htm


The more we study the human body, the more questions we get. I wonder if some future Dr. McCoy centuries from now will we us as we do medicine of two centuries ago. We can go to other planets and invent new tech every day, but the body still holds a ton of mysteries.

I think we often forget that each generation always thinks they are at the peak of technology except for what they are yet to discover or solve. That is of course completely tautological, but there is a point hidden in there! For instance people in a pre-germ era were not in constant reflection on the inadequacy of e.g. miasma theory. Instead miasma theory was taken as an assumption and so things it failed to explain were not attributed to its inefficiency, but as to other things that had yet to be explained or discovered.

So we know everything, except for what we don't know. And we assume that what we don't know is complex, because otherwise we would surely know it. Yet history shows that's often far from the case. It's just that knowing what you don't know is rather difficult, even when the unknown is very simple, simply because you might not even stop to consider such a possibility. People thought the black plague was wrought and spread by evil spirits. They could have easily managed to prove it was being spread by rats, if they were so inclined, but who'd have thought to consider such things at the time?

For a contemporary example we are now discovering that the gut biome is seemingly associated, perhaps causally one way or the other, with all sort of other characteristics of the body and even the mind (as in the autism : gut biome link). We've had the technology to discover this for centuries, but who in the world would think to bother imagining a connection between your gut and anything besides ailments of the stomach?


> People thought the black plague was wrought and spread by evil spirits. They could have easily managed to prove it was being spread by rats, if they were so inclined, but who'd have thought to consider such things at the time?

Well, about that -

https://www.livescience.com/61444-black-death-cause-found-tr...

https://www.pnas.org/content/115/6/1304


Almost certainly. Medical professionals of the future will look at today’s cutting edge med tech the way we view blood-letting and balancing out the body’s humours.

Unlikely. Blood letting and balancing out the body’s humors don’t work. At all. We are quite certain that today’s medical technology works. It could work better, but we can indeed cure ailments that were once considered incurable. Medical professionals of the future will look back on today’s medicine the way we look back on pioneers of science who helped us get where we are today. To say otherwise is a complete insult of the medical professionals who have dedicated their lives to developing better medical technology.

Blood letting does work for some conditions like "hemochromatosis", in many cases a result of genetics + iron intake. https://en.wikipedia.org/wiki/Iron_overload

Not so certainly. Climate change could ravage the world hard and natural resources could dwindle to almost nothing, putting the race in a crude survivalist mindset where there is no time to improve modern medicine or even learn it. Generations of the future may just as likely be looking back at our tech today in awe.

Dr Dale Bredesen has a treatment protocol that improves the conditions of all patients from moderately (late Alzheimer) to significantly (early Alzheimer). His treatment protocol recognizes 3 different types/causes of Alzheimer with an additional 2 subtypes. In December 2018 Dr Bredesen published an article where he shows the results of treatment of 100 patients in various health centers: https://www.omicsonline.org/open-access/reversal-of-cognitiv... It is a shame that Scientific American does not know of Dr Bredesen since he is publishing about his treatment a long time. In 2014 he published an article where he reversed Alzheimer in 9 out of 10 patients (which are still well in December 2018!).

OMICS is one of those fake-journal publication companies. Anyone can publish anything by paying their fee. The paper's own footnote shows this: Submitted October 8, 2018; Accepted October 12, 2018; Published October 19, 2018. No serious journal has a process that quick.

There was a talk at Defcon last year about this. Two journalists from Germany submitted a jibberish paper to one of these companies, got it published, and then they went on a "speaking tour," also organized by these fake journal companies.

http://www.eevblog.com/forum/chat/journalists-find-fake-scie...


After reading the article you linked and browsing his website, I am 100% convinced this person is a charlatan.

This makes me wonder if people who wear contact lenses might be at higher risk as contact lens users regularly touch their eyes.

Ask HN: Are there readily available chemicals that will break down proteins, that would work on prions? How do our digestive systems do it?

Anything that you think of as 'corrosive' will generally break down proteins. Strong bases or acids.

Unfortunately they also tend to break down living tissue too.

Relevant XKCD: https://xkcd.com/1217/


Does a [bullet from a] handgun [effectively] kill cancer cells in a petri dish? I'd expect it to smash the dish and move the cells but except for areas with localised heating not to really do anything else?

Should I actually reconsider having my lasik touched up?

So better skip eye exams?

What eye exam(s) involve physical contact between the eyeball and a medical instrument? Or did a joke just go sailing over my head?

Checking eye pressure involves an instrument touching the eye, and is pretty routine.

My guy uses a machine that does a puff of air. I've never had my eyeball physically touched by anything at an ophthalmologists office.

Lucky you. I've had injections into my eyeball every few years due to a retina issue. Imagine a metal clip holding your eyelid open, and watching the tip of a hypodermic needle approaching your eyeball, held by an older ophthalmologist with shaky hands.

You don't ask your friends if that's normal, and never go back to that eye doctor?

I remember having that done one too, so I looked into it more. There are two types of "tonometry machines", non-contact and contact. The contact tonometers indent your cornea to make measurements (after your eye has been given anesthetic drops). The non-contact "air puff" machines are more common, but apparently not as accurate.

So people who are inclined to avoid direct instrument-to-eye contact can request the "air puff" method.


My optometrist says there are newer and mores accurate methods that don’t require airpuff either, only imaging hardware. I can’t stand air puffs, so it was a relief to find one.

Thank you, my eye tests have always used the air puff.



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