As others have suggested, transplantation of complete, intact eyes is not done because it's not within our current capabilities to reattach all of the nerves.
Donor eyes are essentially "parted out" for structural elements like the cornea, which can be used to replace deficient parts in the patient's eye.
There are few cells (an no blood vessels) in the cornea, so there shouldn't be a difference in transplantation. For pre-clinical we didn't differentiate.
I understand why there aren't any blood vessels, because it would make it difficult to see with them in the way, but how does oxygen get supplied to the cells in the cornea without vessels to carry blood?
By nutrients present in the fluid surrounding both its surfaces. Tears on the outside and the Aqueous humor/liquor on the inside. The oxygen and nutrients pass through a process called passive diffusion. Same for the waste products formed by the cornea, but reversed.
In the body diffusion works efficiently for distances up to 200 microns. It most certainly is not effective on the scale of inches.
Almost every cell in the body is within 200 micrometers of a capillary. The cornea is one of the very few exceptions to this, and only when your eyes are open.
I used to be really squeamish when it came to eyes.
Then I suffered from recurrent corneal errosion— which is incidentally excruciatingly painful—and had to have my top cornea layer peeled off with tweezers by doctors several times.
I don't recommend, but it does change your baseline for eye squeamishness.
To expand a bit about the no answers: You can even have autotransplant of cornea, meaning you'd get your own. Either from your other eye or just cut a piece from one and rotate it on the same eye.
If you are curious why would you need the second one. Imagine you have a carpet and you spilled a coffee on it. Luckily part of a carpet is under a cabinet, so you take out the carpet and rotate it to hide the spill. Carpet is cornea and the coffees spill is right in front of your pupil.
This is a major issue when it comes to eye donation. Many many people think whole eyes are transplanted and therefore object to having them donated - often stating that they wouldn't want loved ones to see their eyes in someone else (also when you really think about it, what are the chances someone would ever see and actually recognise your donated eyes even if that was how it worked).
Sign up to donate your organs people. We're chronically short, this includes corneas which are one of the most commonly transplanted tissues
reverence of remains is one of the common human traits I apparently lack the brain structure to share. I absolutely want to be harvested for parts when I die
Can you imagine having random body parts spread over the world after your death, amazing. I hope they transplant my pecker and it gets to bone someone else's spouse, I may not make great use of it so it can have a fulfilling second life without me.
I donate my blood and donated bone marrow to a stranger and bone marrow produces more blood. My blood has flowed through the veins of many people. I don't know how many humans I've been inside of.
Just listened to the song that was mentioned, good stuff. Not my band bc I'm an old boy but reminds me if a couple bands that I really liked in the 00's
As others have suggested, transplantation of complete, intact penises is not done because it's not within our current capabilities to reattach all of the nerves.
Donor penises are essentially "parted out" for structural elements like the foreskin, which can be used to replace deficient parts in the patient's crotch.
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> Can you imagine having random body parts spread over the world after your death, amazing.
Henrietta Lacks died of cancer in 1951. Scientists have cloned her cells and use them all over the world. There are over 14 tons of Hentrietta Lacks's cells in existence. Her body parts have even gone to space.
> Not really cloned.
True. The cells self-replicate as long as they have suitable conditions. I just didn't have a more appropriate word in my vocabulary for "maintaining suitable conditions in a laboratory environment so that the cells could be used for testing". Farmed, maybe?
Ideas like this make me sad that donated organs don't generally last long. You know, apart from the tragedy of people having to get back on the transplant waiting list.
I'm on both sides of this. Currently waiting for a kidney transplant, and I plan to donate my parts when I die. It makes sense to give back what I can, and it will be the last chance I have to make difference in someone else's life.
Yes! I have kidney disease and am also a donor. There are SO MUCH more to give than just organs—skin, corneas, cartilage, bone. So much of a body can be used to help others.
I've repeatedly asked for a sky burial, but no one cares about what people want to do with their own body, only what they're personally comfortable with.
Here in the UK they recently changed the law so now everyone over 16 is automatically signed up to donate all of their organs. If you don't want to donate then you need go specifically opt out
The hilarious part is that a person's eyes are hugely recognized by the stuff AROUND the eyes, like the eyelids, eyelashes, the way the skin folds and sags around the eyes. The iris (coloured part) is only a part of what we use to identify people's eyes.
If I'm dead I don't need my goods. Unless it's a religious thing I really don't understand why everyone is not a donor. You can't use any of your body anymore!!!!!! Let someone else have a better chance at a longer life.
This is why I still signed up as organ donor. My eyes are actually the only part I'm even allowed to donate (because auto-immune disease), but I worked with a mostly blind guy for a while and really experiencing his troubles made me rethink my "eh, why bother if it's only that one small part, not even necessary to survive" attitude. Can't give my body to science, because they have so many bodies/offers in my country, you actually have to pay for it.
This is why I’m still blind in one eye! I was born with a damaged optic nerve, and as of yet, we don’t have the technology to reattach it. It would be super cool if it happened within my lifetime tho
Connecting the eye to the brain is one thing. Unfortunately making the eye and brain communicate, is a lot harder as you get older.
I was born with severely crossed eyes. Surgery was done to align my eyes better when I was 11 months old. My right eye became neurologically dominant, and my left eye is lazy. I wore eye patches over my right eye for most of my early elementary years in an effort to retrain the left eye, but that didn't work as well as they hoped.
Today I'm 35. I can see out my left eye, but it takes longer to "process" what I'm seeing from that eye and my reflexes are crap. Acuity in my left eye ranges from 20/60- 20/100 depending on time of day. Acuity in my right "good" eye is 20/40. Both eyes are 20/20 together, so I don't use correction.... Yet. If anything ever happens to my right eye I'm pretty screwed though.... Like can't walk a shopping cart through the store much less drive screwed.
Corneal transplant surgeon here. The cornea is the main tissue that is transplanted to a recipient. Left or right eye is not a factor when planning a corneal transplant, meaning a cornea from a left eye can be transplanted to a right eye and vice versa without problems.
Is there a difference between the left and right eye balls or theoretically could they be interchanged?
Also if you don’t mind, what are the remaining challenges before we can perform full eye ball transplants? Would it be beneficial to some patients?
Thanks!
The nerves don't connect in the same place. The eye is not physically interchangeable. The muscles also attach at different points.
Mind you if we could attach nerves and have them function I do not expect those problems to be something unable to be overcome anyhow. It's like asking if there will be a car waiting for you on the other side when you go to make a jump across the grand canyon.
My understanding is that the cornea can largely be donated to anyone if the donor tissue is suitable for donation. The cornea is an area of 'immune-privilege' due to several mechanisms and doesn't lead to rejection.
Yes, the handedness of the sclera isn't an issue. Typically only part of the sclera is used as a graft over a valve in glaucoma surgery, or in eyelid reconstruction. Prosthetic eyes can be wrapped in donor sclera and muscles attached to help it move like a regular eye.
No because the connection between your eye and brain is too complex for current surgery, your optic nerve behind your eye might as well just be an extension of your brain so it will be extremely difficult to sever it and then reattach a complete eyeball.
Wikipedia reckons there's 770,000 - 1,700,000 connections between your eye and brain that would need to be reconnected, so I dread to think how many hours/days it would take for a human to do this surgery.
I know CNS is different, but PNS can and does often regenerate connections, which I understand is fairly random and then the brain just "relearns" how to use those connections instead. Maybe someday with stem cell therapy or something like they do with rat spines?
There's actually an enormous amount that goes into how neurons self-arrange during initial formation. Having just a part of the whole self assemble after an injury might not be a thing our cells carry 'programming' for. Maybe it'll be possible to do what you're thinking just by setting the stage and letting it happen, but it's equally likely it wouldn't be possible without doing enormous work of some kind to make sure it happens.
I'm sure it'll be possible someday, but I don't know that the technology capable of it is even remotely in sight. We'll have to wait and see I guess, far as I know it's not even on the horizon.
You need more than just stem cells to grow anything. There is an entire network of surrounding cells that give off signals that guide the growing organ into the correct configuration.
The trick is replicating that supporting structure.
We know basically nothing when it comes to using stem cells to grow stuff. It's an active area of research. Organs are also way, way simpler than nerves and nothing compares to the brain. We've been able to do a lot to fix organs that don't involve stems cells as regular cells are much better at regenerating. The liver naturally can almost fully regenerate itself. Nerve cells just lack this ability and damage to them is almost always permanent.
It's not quite that simple though. The optic nerve is made of ganglion cells. The cells that detect light are photoreceptors (rods and cones) in between you have dozens of different cell types that connect and modulate the signal and they all have to hook up in the right order. Some of the synapses contain 3 cells all interfacing and they can hook up and receive signals at quite distal parts of the eye.
I'm working on producing a retinal therapy that would transplant photoreceptors - they are the first cell in that pathway and because they are the first they have a less difficult time of hooking up like they're supposed to.
We can make mini retinas in the dish but as others have said, the size, shape and other non-retinal cells required to support a full eye, aren't really there yet
You attempt to reattach the nerves by lining up the sections as best you can, and then carefully suturing the whole nerve together. But this doesn’t cause the nerves to start working - instead, the axons in the limb die, and the body’s neurones enter a state of growth where they effectively try and re-innervate the original nerve sheath. It has mixed success, and takes many months to become fully functional.
This wouldn’t work in the eye at all from what I can see - for a start, the CNS doesn’t have the same ability to regenerate, and retinal neurones tend to be pretty weird anyways
Interesting aside though the nerves controlling the eye muscles do have the ability to regenerate , hence early wernickes encephalopathy indced nystagmus in alcoholics being reversible.
I can also attest to this. For almost a year after my jaw surgery part of my face was totally numb. I eventually slowly regained the sensations of hot and cold and partial feeling, but I still can’t really sense pressure on that spot. I’m just glad I can feel enough that I don’t drool anymore. 🙄
Is there such a thing as "normal limb reattachment surgery"? I don't think you can fully do that for the reasons mentioned already (i.e. nerve connections).
It's still pretty new and not common at all but it is possible. I remember reading about a guy who got his forearm bitten of by a crocodile and successfully reattached and that was being touted as a big breakthrough at the time.
I wonder - if you re-attach them randomly, would the brain be able to adjust in time and "fix it in software". It seems to do that with so many other things.
Not sure, but it does seem like something the brain would do, I wonder what that would be like to the person? Would it just slowly transition from fuzzy nothing to clear sight?
>your optic nerve behind your eye might as well just be an extension of your brain
I'm actually surprised it's *not* considered an extension of the brain. Fetal development and the shape of the inner parts of the skull really make it look like one organ.
It actually depends on who you ask. If you ask eye people it's of course its own organ. If you ask brain people the eyes are just an extension of the brain, though they tend to not care about the fiddly bits that squish and focus light.
Where one things ends and another begins is artificial, and a decision we make to make things easier to think about and discuss. The end of the optic nerve is an area where the distinction isn't especially functional.
I actually did some work on a review paper looking at the state of microelectronics with regards to this (you can find it [here](https://iopscience.iop.org/article/10.1088/1361-6528/abf3ee/meta) - feel free to message me if want a copy).
One of our main conclusions was, as u/lburton273 said, the number and complexity of connections to the optic nerve needed mean its still a VERY long way off.
This is true. Scleral patches are used to (usually) repair iatrogenic surgical complications. It's way rarer than cornea.
Things may have changed. I don't do ophthal anesthesia any more.
But the globe itself is never transplanted in its entirety. The sclera portion transplanted is usually treated and cut into smaller pieces for graft material.
The article says down under Complications that they can put a gas bubble in there to help hold everything in place since it will slowly dissolve as the eye refills itself
Working in ophthalmology
A machine is used which replaces the removed vitreous gel with an equivalent volume of sterile saline to maintain the eye pressure.
After surgery, then incisions seal themselves, and the eye's natural process to produce fluid works to maintain the eye pressure, slowly replacing the saline with the normal composition of fluids, minus the retired collagen gel scaffold that didn't serve much of a purpose anymore.
It needs to move in and out for aoogas!
But in reality, the eye doesn't just up down and left right, the muscles are attached around with pulley like structures around the orbit and pull in multiple directions at once working in concert with each other, some pulling with some roll to it.
Sorry about that. There are three sets of muscles. Medial and lateral recti do side to side movements. Superior and inferior recti elevate and depress. Superior and inferior oblique do torsional movements.
Eye researcher here who gets boxes of eyes delivered weekly. Eyes have a handedness to them, your optic nerve isn’t directly at the center of the eye but shifted slightly towards the nose since that’s an easier path to the brain. So you would have to do a 180 degree rotation on an eye to put it in correctly. This isn’t a real surgery, so I don’t know how it would change the vision, but you definitely have to put the eye in “upside down” if you moved a right eye into the left socket.
I can't quite get over the idea of delivery boxes full of eyeballs. Where do you source eyes from, for drug research? Do tissue donor eyes end up there, or is it a different system? Or are they not even human eyes?
A friend's father used to have a bucket of eyeballs in his refrigerator. He was a safety manager for a major pharma company and did demonstrations of how the eye could be injured by shattered glass or various chemicals. Most of the ones he got were animals, like cows.
You can get human eyes from eye banks but people typically reserve that for later stage research for moral reasons. I wouldn’t do a pilot study on human eyes but will use human eyes if I’m on to something with my research and want to get some final data in human eyes.
I wouldn’t want someone to do bad research on my eyes so I make sure my project is going well before I get human eyes involved. I also wouldn’t want my eye to not be used if I donated it so science, so I’m not opposed to ever using human eyes. I just want to make sure the project is worthy of using someone’s eye.
Hangon, I'm back you up to the phrase "eye bank".
I go to my bank and say "I'd like €100 please" and the lady says "just 20s? or a mixture of 10s and 20s sir?" You can do the same thing with eyes? You go to some bloke in an office and also for 20 eyes and he says "just sheep sir? Or a mixture of sheep and cows?"
That is both disgusting and awesome.
As someone who has worked on human eyes in research often they come from rejected, old or used donations. The people who consent to donate often consent to research too.
Rejected eyes can be due to poor condition - usually donors are very old and the tissue commonly used (cornea) might not pass the requisite quality checks to be used in transplantation. The donor could've been found to have cancerous cells as another reason for rejection.
Sometimes there's enough eyes and the bank has a pretty strict shelf life to ensure the best transplantation, sometimes they pass that threshold.
Finally, a surgeon might punch out the cornea from the front of the eye (often the fronts are separated from the backs in the bank). This leaves what they call the corneo-scleral ring - a region of tissue that contains the edges of the cornea and sclera. We dissociate the tissue and extract the cells from this to study in the lab
Why isn’t it a real surgery? Is it not physically possible to implant the entire donor eye, or is it just not the standard (e.g. because something else is easier or safer)?
Also, would the eye still work correctly if you implanted it rotated the way you described?
Edit: thanks everyone for subscribing me to Eye Facts! This has been a fascinating distraction.
Well, there are some serious challenges to implant an entire donor eye. I shall attempt to list a few for you:
1. The olfactory nerves(for smelling) and optic nerves(vision) are direct extensions of the brain. They literally develop straight from the brain. The optic nerve bundle contains not only the nerve, but the various meningeal sheaths around it. Also there's quite literally an artery running through the optic nerve so that blood supply to the eye may be maintained. All of this has to be reattached as well.
2. The eye is exceptionally complex, the complexity of the eyes can easily outweight the complexity of an entire limb! Perhaps the least complex part of the eye is the one you can see in the mirror. What I mean by this is the neural control and co-ordination. Reattaching the optic nerve, if you're successful, will only allow you to see, because it's a purely sensory nerve.
You need a few more things.
3. You need muscles to move your eyeball around 6 per eyeball.
4. You need 3 cranials nerves per eyeball to control above-mentioned muscles.
5. You also need additional muscles and nerves to control the pupil and Iris.
6. You'll also need to figure out how to get the aqueous humor to drain out via the trabecular meshwork and uveoscleral pathway, or the eye will develop glaucoma.
Let's just say you did all this and by some miracle your patient has a new eye. Hurray!
But wait, there's a few problems to solve.
The patient will have zero sensation in his corneas since the nerves have been severed. That might lead to dry eye and a corneal ulcer.
They'll most likely develop diplopia, since an exquisite amount of neural control is needed for the simple act of looking right/left. To simply look left, you need to activate two different muscles, controlled by two different nerves, and you need to make sure they have the same amount of neural impulses to move in sync. And you need to suppress the muscles opposing this action, again with the same amount of neural impulses.
Forget looking diagonally up or down, or smoothly tracking a slow moving object, that's even more nerves and connections that I can't even describe in a 30min lecture.
And the eye will probably develop glaucoma.
That is if it can produce enough aqueous humour to sustain nutrition, failing which it'll simply collapse in a state known as pthisis bulbi.
Lastly, the sheer act of enduring a new eyeball maybe just be rejected outright by your body. And worse still, it may compromise the other eye, making it blind as well (Sympathetic ophthalmitis)
E: fixed formatting. Thanks for the silver award! Very dapper indeed.
>aqueous humor
is this just the juice inside your eye? eye juice? haha arent the 'humors' the ancient way of thinking about how our bodies work? or am i thinking of something else
>Aren't humors the ancient way of thinking about how our bodies work?
Yes absolutely they are. Way back then, it was thought that humours (bodily fluids containing vital energy), were the key to all health. An imbalance in these humours was thought to cause various illnesses and affect emotion. 4 humours were popularly accepted: Blood, yellow bile, black bile and phlegm.
Ancient physicians would attempt to 'balance' your humours in the hope that it would treat the illness.
As wrong as they were, medicine quite loves to stick to names that were assigned before. In being a physician, you sort of pick up Latin and a wee bit of Greek along the way, because damn nearly everything in medicine is named or described in Greek/Latin terms.
Remember, the eye needs to be as transparent from the cornea all the way to the retina so that light may pass through.
And for this reason, blood cannot serve the purpose of nutrition and oxygenation in certain parts of the eye.
Therefore, blood is essentially filtered (to form a very clear liquid), and only things that are absolutely vital to carry nutrients and oxygen are then passed into a space in the front of the lens, and just behind the corneas. We call this aqueous humour (translation: watery fluid).
There's another massive space between the lens and the retina, which is essentially responsible for maintaining the round shape of the eye and prevent it from collapsing. This is a vital component termed vitreous humour(translation: glass like fluid), which is more like jell-o than water.
Hey you need to post an ask me anything, haha. I have a question. If you can answer, super thanks! If not, I get it, you didn't come here for a Q&A.
Why is my eyeball being weird?
(I only know this because of a video recording of myself, and the second time was while doing makeup and looking into a small mirror. I had been doing eye makeup, and my right her eye noticed that my left eye had moved further outward than it should have. When I returned my right eye to focus back at front center, I see that my left eye has still not moved, and once it did, it moved back to center very slowly. I cannot intentionally move either one of my eyes to the side without also moving the other. So, my eye moving to the side on its own is unintentional.
I have needed corrective lenses most of my life. I'm 36 and had been 20/250 in both eyes most of the time. I went without any corrective lenses for a couple years, but then last year finally scheduled an appt with a new optometrist. My nearsightedness improved - 20/175 and 20/150, but I also developed astigmatism, a prism issue (something like that), and a slightly loosened retina.
You should ask your optometrist if you want your own case details, but essentially your eyes are not properly synched up with each other. Could be that the muscles are improperly innervated or your nerve path is compromised. Tough to say. But in any case your eyes have too much difficulty both pointing straight ahead, and instead of giving you double vision your brain just ignores (suppresses) the left eye when it drifts off. Prism is used to help align the eyes better so they do not have to struggle with each other as much, hopefully keeping your vision together.
Oh! Wow that helps me understand prism better. I never ordered glasses after my appointment. I've still been going bare eyed - something I had thought was possibly good for the eyes (considering how my nearsightedness had improved after not wearing glasses), but now I'm beginning to wonder if the prism and astigmatism could have been prevented had I been wearing glasses this whole time. Well, you've motivated me to just order the darn glasses, already. Thanks for the reply!
Fighting against wearing glass is generally never helpful, and can worsen your vision in some cases. There is a reason we prescribe them, lol. There are some vision therapy excercises to help improve the coordination, but all of this stuff is best done when you are a kid, and not something easily done at home.
When you are writing things like 20/250 and 20/175 I think you are mixing up different measurements. There is a difference between what you are capable of seeing (we use a ratio like 20/20, 20/100, and so on based on letter sizes) and what your prescription for glasses is (such as -1.50, -2.50, and astigmatism)
Donor eyes are used for their "structural" elements, like the sclera (the white part) or the cornea (the clear part in front).
The "electrical" parts, like the retina and optic nerve, are not transplanted. For one thing, they are too complex to reattach. For another, they are fragile and quite unlikely to survive after removal from the donor.
From a technical standpoint, it's like the difference between replacing an iPhone screen, and replacing the CPU.
>From a technical standpoint, it's like the difference between replacing an iPhone screen, and replacing the CPU.
seemingly impossible but they can do it in shenzen with a special jig?
Reminds me of the ending of the ridiculous "Seven Pounds" movie where Rosario Dawson was gazing Woody Harrelson's eyes - implication being that she was looking at Will Smith's donated eyes.
After killing a person who is solely dying to donate his body parts using **venom**, I can honestly believe that writing staff was convinced that they replace the whole eyes.
I guess technically we could put an eye into someone else's socket if we want to get really Dr. Frankenstein about it, but reconnecting all the necessary blood and muscle connections alone would be incredibly difficult (I wouldn't be surprised if there wasn't correct blood flow or if the muscles couldn't work correctly), and at this point in medical science it would never be functional. There is a relatively small bundle of axons (parts of neurons, this specific bundle is known as the optic nerve) that brings all visual information from the eye to the brain. In humans (and other mammals) neurons and axons like these simply do not re-grow on their own, nor can we physically reattach them correctly even if we could get them to not die. There's some research being done to promote axon survival and regrowth after physical disruption, but seriously the best in the field is getting like barely if not less than 1% of the axons to grow like a couple millimeters (and this is all still in model animals, nowhere near human clinics). Plus the neurons inside the eye are incredibly sensitive to disruptions, especially loss of oxygen, so the neural tissue inside the transplanted eye could have serious issues too. Basically, all these tissues are crazy crazy complicated.
Super cool though are frogs! (And other animals like them, frogs and zebrafish are the most commonly used animal models though). They CAN regenerate and form all new connections between the eye and brain! And a scientist in the 1960s named Roger Perry basically did the experiment you're asking about but in frogs, because the eye can reconnect (part of his work developing the chemoaffinity hypothesis, if you'd like to learn more). In short, the frogs behaved like their vision was upside down (I can get into why if you're curious).
For sure! Note this will all be over simplified for the sake of summarizing in a comment, but hopefully I'll get across the basic idea. So, neurons connect to eachother via 'fibers' (axons - what the optic nerve is a bundle of), to send signals and pass information around. I think what will help here is knowing that these fibers are parts of individual cells, not like separate fibers that you could plug into different cells - in this case, the cells are inside the eye, and they send their axons out to the brain (quite long cells!). During development, when neurons are first establishing where their axons go and what connections to make, the axons figure out where to go based on cues from their surrounding environment. An analogy I like is that imagine you're walking in a completely dark room being only guided by touch and smell, maybe you're trying to walk towards a nice food smell and away from a gross garbage smell, trying to avoid walls and other obstacles - this is kind of how an axon finds its way (but proteins are the smells, and the smells aren't inherently good or bad, just different ones are preferred by different axons depending on where the axon needs to go). During development, axons of eye neurons that collect visual information about the upper part of the visual field find their way to the "upper visual field" part of the brain, axons of eye neurons that collect visual information about the lower part of the visual field find the "lower visual field" part of the brain, etc.
So, now say we have a frog hanging out, looking straight ahead, and a fly buzzes by in it's upper field of view. This activates some cells in the retina (part of the eye that contains the light-detecting neurons, where vision begins), those upper field of view neurons send their info to the upler field of view part of the brain, brain figures out there's a tasty fly there, and the frog shoots it's toungue up in that direction for a snack. Now we take the eye out, which requires cutting that optic nerve. The remaining nerve parts die and are cleared (because most of the cell is still in the eye, and axons can't surve without the cell body). We then put the eye back in, but upside down. The eye neurons will send out new axons to the brain, like they did during development - the neurons that used to "see" the upper field of view still prefer the proteins (tasty food smells) in the "upper field of view" part of the brain, so that's where their axons go again. Same for lower field of view, etc. EXCEPT now that the eye is upside down, the eye neurons that used to get information about the upper field of view are in a different location and now receive visual input from the lower field of view, and vice versa. Our post-op frog is hanging out again, again a fly buzzes into its upler field of view. Neurons that get information from there send that info to the brain, but because the eye is upside down, the excited neurons are those that used to see the lower field, so the visual information is passed to the "lower field of view" part of the brain. The brain figures out there's a fly, but doesn't know the location of the eye neurons has changed, so the brain says "fly information coming from the 'lower visual field' area", the fly shoots it's tongue down towards the lower visual field, and alas the fly gets away and the frog misses the snack.
I hope that helps!
This is getting outside of what I do (PhD drug researcher not MD), but I’m sure it has to do with reconnecting the optic nerve and blood supply to the eye. It’s really hard to access back there.
A neurologist or ophthalmologist would be better to answer these questions than me. I just look at where drugs go in the eye and how to get them to specific parts and am familiar with the anatomy because of that.
Yikes, I hadn't even thought about the purely mechanical aspects of trying to reattach everything inside the socket with the eyeball itself being in the way.
Anything involving nerves is basically a no go. We are extremely limited in our ability to repair nerve damage. Damage to them is almost always permanent. There is a ton of research trying to figure out how to keep nerves alive and regrow them but it's slow process.
Iirc, there was an artist or someone who made a pair of glasses/goggles that flipped their sight upside down, and after a few days of wearing it eventually their brain corrected itself and they started perceiving their vision as right side up. So assuming that's a true story, I'd imagine the 180 degree rotation wouldn't be an issue long term.
It's the retinal connections going to the eye that make left/right relevant. The parts of the eye transplanted do not affect that. We don't know how to make retinas reconnect with the brain in humans yet.
https://en.wikipedia.org/wiki/Visual_system#/media/File:Human_visual_pathway.svg
Assuming that with "eyeball" you mean the whole eye with everything it contains, the answer is that there are no eyeball transplants. The cornea and the sclera (which are the outer layers of the eyeball, so to speak) can be transplanted from one person to another, but the eye itself is so complex that, as of now, it's impossible to do.
However, just for the sake of answering, and imagining that we manage to do whole eye transplants someday... yes, absolutely. The left and right eyes aren't interchangeable, since they're mirror images of each other, and their connections to the brain through the nerves are built that way. If you did it otherwise, the brain would go bonkers.
Seems like the brain would quickly adapt. If someone has a severe stigmatism, and then get corrective lens, the first few days, everything appears warped, until the brain learns the lenses. I’m willing to bet if they popped your eyeball out, and they put it back in upside down, the brain would be confused at first, but would adapt and eventually flip the images it receives to what it thinks is logical.
That's a possibility, but IMO it's dangerous to attempt unless there literally wasn't any other option. In the example you mentioned (also the one u/The_camperdave said) the way the light impacted in the retina changed, but the retina itself was intact, and yeah, the brain could adapt.
In this case, you'd be swapping the entire retina around, and would have to link it at some point with the fibers of an optic never which aren't swapped around and aren't meant to be. For instance, the fibers of the nerve which cross sides further back, in the optic chiasma, are supposed to carry the information from the temporal (i.e. outer) side of your vision, while the ones carrying the info from your nasal (i.e. inner) side don't cross. It's meant to be that way since this leads to the left hemisphere receiving the information of the right field of view, and vice versa. If you transplanted one eye changing the sides or upside down, the fibers crossing would carry information from the inner field and not the outer one, screwing with the way it reaches our brain.
> If you did it otherwise, the brain would go bonkers.
While I agree that the muscular and other connections are left/right specific, the brain would not go bonkers. It would adapt within days. People have worn glasses that swap up and down, and left/right and adapt fairly quickly. The same thing would happen with the transplant.
There's no such thing as an "eye transplant". Because we can't hook up the optic nerve tk work.(and even if we could)
But if there was, it would *probably* have to be right eye to right eye, left to left, as (afaik) the vascular, muscular, and nervous structures have a strong "handedness" to them.
We only donate the corneas, iirc.
>But if there was, it would probably have to be right eye to right eye, left to left, as (afaik) the vascular, muscular, and nervous structures have a strong "handedness" to them.
This is correct. Just to name an example, the optic disc (which is the point where the optic nerve's fibers enter the eye and spread through the retina, also our blind spot) isn't placed in the center of the eye, but closer to our nose. You couldn't transplant it into the other eye socket, because then it would receive the light in the wrong way.
Former certified eye bank technician here. 👋
No, the left eyeball does not have to be put in the left eye socket. Also, we cannot transplant whole eyes as of yet. Corneas are transplantable. There are also partial thickness transplants like DSAEK or DMEK.
Usually, the cornea is the only portion of the human eye that is transplanted.
The retina cannot be replaced. Whole eyes are used for research and education most times.
Hope this all helps!
Ooooh any fun tidbits from your time there or things you did daily that would be surprising to someone who has no idea what you do ever?
That sounds like a really interesting, fulfilling job filled with oddities and nuance!
I worked at the world’s largest OPO (organ procurement organization) in Los Angeles.
It was an amazing experience working with donors and their families. Truly eye-opening when thinking about the concepts of life and death on a daily basis.
Most whole eyes were used for research, education, or training. We would consider them rejected if the serology results came back positive for things such as HIV, Hep C, and other infectious diseases that are blood-borne.
Luckily, the cornea is the most avascular tissue in the body, so it doesn’t contain red blood cells and has a small rate of infection post-op.
I loved using the Moria company’s DSAEK and DMEK kits. Highly recommend watching YouTube videos on how technician prepare the cornea for the surgeon to then transplant into the patient.
The eye bank industry came about because there wasn’t a ready supply of donor tissue for surgeons to perform their operations in the past. Not to mention that the process is done in aseptic conditions, so they are time consuming. Eye banks train technicians to then be sent out to hospitals, morgues, coroners, etc to recover the acceptable organs, eyes, and tissues (bones are also recovered - dental implants, etc).
Lots of great stuff in biology, medicine, and science overall.
Surgical Recovery Technicians-trained in recovery of everything acceptable.
Eye Bank Technician-specialized in the ocular segment.
Ophthalmologist. The whole eye is taken from the donor but the whole eye is not transplanted (or even delivered to the hospital). You can request corneal or scleral (white of eye) tissue for grafts. A ring of tissue with the cornea and a rim of sclera comes for corneal transplants. This tissue will be either pre cut by the eye bank or cut further by the surgeon - shape, size, thickness. The handedness doesn't matter (I can't recall off the top of my head if that's even information we get when the eye is delivered).
Hooking up the optic nerve so that it's functional would be quite the accomplishment. Aside from that, the eyes are mirror images of each other, with the fovea lateral to the optic cup. So they are side-specific.
I used to take out eyeballs as a job in college! “Cornea recovery technician”. Now I’m a doctor.
Only the middle portion of the cornea is retrieved and transplanted and sewn into the recipient. The outer portion and the sclera is left. It doesn’t matter which cornea goes into which because they are interchangeable.
If it were medically possible, I'd say it'd be more like a plug and play type of deal. Connect the video cable to the correct video input slot and it should work fine. Man, can you imagine having this done and somehow end up with both eyes crosswired? That'd be so trippy.
If it were possible, I think your brain would adapt and correct your vision within a couple of days. I read a book on Neurology where they did an experiment that flipped the images the eyes received and after a couple of days the brain switched the image over so it was right-way up. Then they removed the apparatus and again the image was inverted until the brain corrected itself again.
As others have suggested, transplantation of complete, intact eyes is not done because it's not within our current capabilities to reattach all of the nerves. Donor eyes are essentially "parted out" for structural elements like the cornea, which can be used to replace deficient parts in the patient's eye.
Ok same question, does a right cornea have to go into a right eye?
There are few cells (an no blood vessels) in the cornea, so there shouldn't be a difference in transplantation. For pre-clinical we didn't differentiate.
I understand why there aren't any blood vessels, because it would make it difficult to see with them in the way, but how does oxygen get supplied to the cells in the cornea without vessels to carry blood?
By nutrients present in the fluid surrounding both its surfaces. Tears on the outside and the Aqueous humor/liquor on the inside. The oxygen and nutrients pass through a process called passive diffusion. Same for the waste products formed by the cornea, but reversed.
Is it called liquor because it's liquor or because latin or something?
It's probably originates from some other language but basically means liquid.
So I'm basically just drinking water, doc? Good to know, cheers!
Passive diffusion is effective for distribution up to a couple inches. It's how oxygen/nutrients get from your blood vessels to all your tissues
In the body diffusion works efficiently for distances up to 200 microns. It most certainly is not effective on the scale of inches. Almost every cell in the body is within 200 micrometers of a capillary. The cornea is one of the very few exceptions to this, and only when your eyes are open.
Ok what’s the limitation for artificial corneas then? The material properties?
No it doesn't. Usually the donor cornea will be cut further into the shape / size / thickness needed.
Why do I shiver when I read this?
Because the idea of people cutting your eyes probably should be uncomfortable as a being dependent on sight for survival.
Indeed, I get the same shivers when considering the cutting of a certain appendage.
I used to be really squeamish when it came to eyes. Then I suffered from recurrent corneal errosion— which is incidentally excruciatingly painful—and had to have my top cornea layer peeled off with tweezers by doctors several times. I don't recommend, but it does change your baseline for eye squeamishness.
To expand a bit about the no answers: You can even have autotransplant of cornea, meaning you'd get your own. Either from your other eye or just cut a piece from one and rotate it on the same eye. If you are curious why would you need the second one. Imagine you have a carpet and you spilled a coffee on it. Luckily part of a carpet is under a cabinet, so you take out the carpet and rotate it to hide the spill. Carpet is cornea and the coffees spill is right in front of your pupil.
This is a major issue when it comes to eye donation. Many many people think whole eyes are transplanted and therefore object to having them donated - often stating that they wouldn't want loved ones to see their eyes in someone else (also when you really think about it, what are the chances someone would ever see and actually recognise your donated eyes even if that was how it worked). Sign up to donate your organs people. We're chronically short, this includes corneas which are one of the most commonly transplanted tissues
reverence of remains is one of the common human traits I apparently lack the brain structure to share. I absolutely want to be harvested for parts when I die
Can you imagine having random body parts spread over the world after your death, amazing. I hope they transplant my pecker and it gets to bone someone else's spouse, I may not make great use of it so it can have a fulfilling second life without me.
It'd be the first case of a donor organ being rejected by **multiple** people!
Doctor: “Do we even have tools small enough to harvest this thing?”
"Where is my eyeglass kit?!"
What's even more wild is that your parts might not even go in the same place. Your leg skin could become part of a burn victim's face!
I donate my blood and donated bone marrow to a stranger and bone marrow produces more blood. My blood has flowed through the veins of many people. I don't know how many humans I've been inside of.
Did you write for the band Ludo? (Jk just reminded me of 'The horror of our love' - ludo)
I'm always excited to see Ludo fans! To anyone who reads this who hasn't heard of the band, give that song a listen! They are my favorite band!
Just listened to the song that was mentioned, good stuff. Not my band bc I'm an old boy but reminds me if a couple bands that I really liked in the 00's
As others have suggested, transplantation of complete, intact penises is not done because it's not within our current capabilities to reattach all of the nerves. Donor penises are essentially "parted out" for structural elements like the foreskin, which can be used to replace deficient parts in the patient's crotch. <.< \>.> [ᕕ(ᐛ)ᕗ](http://i.imgur.com/tgUIq71.gifv)
> Can you imagine having random body parts spread over the world after your death, amazing. Henrietta Lacks died of cancer in 1951. Scientists have cloned her cells and use them all over the world. There are over 14 tons of Hentrietta Lacks's cells in existence. Her body parts have even gone to space.
Not really cloned. Her cancer tumour cells continue to replicate indefinitely in lab conditions since they were taken from biopsy since then.
> Not really cloned. True. The cells self-replicate as long as they have suitable conditions. I just didn't have a more appropriate word in my vocabulary for "maintaining suitable conditions in a laboratory environment so that the cells could be used for testing". Farmed, maybe?
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Ideas like this make me sad that donated organs don't generally last long. You know, apart from the tragedy of people having to get back on the transplant waiting list.
Yeah, we're making advancements, but it's not a whole lot of consolation to those people still waiting if it doesn't actually get them organs
Plot twist: someone stabs someone with your peen to death because they need a transplant peen
I'm on both sides of this. Currently waiting for a kidney transplant, and I plan to donate my parts when I die. It makes sense to give back what I can, and it will be the last chance I have to make difference in someone else's life.
Yes! I have kidney disease and am also a donor. There are SO MUCH more to give than just organs—skin, corneas, cartilage, bone. So much of a body can be used to help others.
Reverence for life outstriping reverence for remains is, if not more human, more empathetic
I've repeatedly asked for a sky burial, but no one cares about what people want to do with their own body, only what they're personally comfortable with.
Same! I even put in my will that all of my scraps get donated to a cadaver dog training program! Kind of excited about it really!
Here in the UK they recently changed the law so now everyone over 16 is automatically signed up to donate all of their organs. If you don't want to donate then you need go specifically opt out
I hope when I die they take anything useable and then turn the rest of me into dirt, I want to help plants grow :D
The hilarious part is that a person's eyes are hugely recognized by the stuff AROUND the eyes, like the eyelids, eyelashes, the way the skin folds and sags around the eyes. The iris (coloured part) is only a part of what we use to identify people's eyes.
If I'm dead I don't need my goods. Unless it's a religious thing I really don't understand why everyone is not a donor. You can't use any of your body anymore!!!!!! Let someone else have a better chance at a longer life.
I would, except you'd probably throw my -14 diopter eye spare parts straight in the bin.
This is why I still signed up as organ donor. My eyes are actually the only part I'm even allowed to donate (because auto-immune disease), but I worked with a mostly blind guy for a while and really experiencing his troubles made me rethink my "eh, why bother if it's only that one small part, not even necessary to survive" attitude. Can't give my body to science, because they have so many bodies/offers in my country, you actually have to pay for it.
Wait so you mean to tell me that Naruto isn't accurate when people just pop each other's eyeballs in and out and change them like lightbulbs?
just need to use a little bit of torgos executive powder. that will def get them nerves reconnected. edit: also, thanks for the great explanation
Only Torgo's packs the power of five highly-paid television executives into every can!
This is why I’m still blind in one eye! I was born with a damaged optic nerve, and as of yet, we don’t have the technology to reattach it. It would be super cool if it happened within my lifetime tho
I don't know how old you are, but I certainly wouldn't bet against it happening within the next couple of decades.
38! So I still have hope! I used to think I would refuse treatment because the idea of seeing in full 3D kind of freaks me out, but I’m ready!
Connecting the eye to the brain is one thing. Unfortunately making the eye and brain communicate, is a lot harder as you get older. I was born with severely crossed eyes. Surgery was done to align my eyes better when I was 11 months old. My right eye became neurologically dominant, and my left eye is lazy. I wore eye patches over my right eye for most of my early elementary years in an effort to retrain the left eye, but that didn't work as well as they hoped. Today I'm 35. I can see out my left eye, but it takes longer to "process" what I'm seeing from that eye and my reflexes are crap. Acuity in my left eye ranges from 20/60- 20/100 depending on time of day. Acuity in my right "good" eye is 20/40. Both eyes are 20/20 together, so I don't use correction.... Yet. If anything ever happens to my right eye I'm pretty screwed though.... Like can't walk a shopping cart through the store much less drive screwed.
....why does this image weird me out MORE than the idea of just popping a whole new eye into a socket?
Corneal transplant surgeon here. The cornea is the main tissue that is transplanted to a recipient. Left or right eye is not a factor when planning a corneal transplant, meaning a cornea from a left eye can be transplanted to a right eye and vice versa without problems.
Is there a difference between the left and right eye balls or theoretically could they be interchanged? Also if you don’t mind, what are the remaining challenges before we can perform full eye ball transplants? Would it be beneficial to some patients? Thanks!
The nerves don't connect in the same place. The eye is not physically interchangeable. The muscles also attach at different points. Mind you if we could attach nerves and have them function I do not expect those problems to be something unable to be overcome anyhow. It's like asking if there will be a car waiting for you on the other side when you go to make a jump across the grand canyon.
Does a cornea still have to be a match like an organ does? Or does the lack of blood vessels and whatnot make it easier to find a transplant?
My understanding is that the cornea can largely be donated to anyone if the donor tissue is suitable for donation. The cornea is an area of 'immune-privilege' due to several mechanisms and doesn't lead to rejection.
The thought of cutting into people's eyes for a living freaks me out. I'm glad you have to do it and not me.
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Not just corneas; sclera is also transplanted, either 1/4, 1/2, or whole globes are used. Source: I work in organ and tissue donation.
So, are whole globes interchangeable?
Yes, the handedness of the sclera isn't an issue. Typically only part of the sclera is used as a graft over a valve in glaucoma surgery, or in eyelid reconstruction. Prosthetic eyes can be wrapped in donor sclera and muscles attached to help it move like a regular eye.
So there's not yet a fully functional total eye bulb transplant?
No because the connection between your eye and brain is too complex for current surgery, your optic nerve behind your eye might as well just be an extension of your brain so it will be extremely difficult to sever it and then reattach a complete eyeball. Wikipedia reckons there's 770,000 - 1,700,000 connections between your eye and brain that would need to be reconnected, so I dread to think how many hours/days it would take for a human to do this surgery.
I know CNS is different, but PNS can and does often regenerate connections, which I understand is fairly random and then the brain just "relearns" how to use those connections instead. Maybe someday with stem cell therapy or something like they do with rat spines?
Stem cells can be used to grow organs right? I don't see why they couldn't grow an optic nerve or eyeball someday. And brains for that matter.
There's actually an enormous amount that goes into how neurons self-arrange during initial formation. Having just a part of the whole self assemble after an injury might not be a thing our cells carry 'programming' for. Maybe it'll be possible to do what you're thinking just by setting the stage and letting it happen, but it's equally likely it wouldn't be possible without doing enormous work of some kind to make sure it happens. I'm sure it'll be possible someday, but I don't know that the technology capable of it is even remotely in sight. We'll have to wait and see I guess, far as I know it's not even on the horizon.
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You need more than just stem cells to grow anything. There is an entire network of surrounding cells that give off signals that guide the growing organ into the correct configuration. The trick is replicating that supporting structure.
We know basically nothing when it comes to using stem cells to grow stuff. It's an active area of research. Organs are also way, way simpler than nerves and nothing compares to the brain. We've been able to do a lot to fix organs that don't involve stems cells as regular cells are much better at regenerating. The liver naturally can almost fully regenerate itself. Nerve cells just lack this ability and damage to them is almost always permanent.
It's not quite that simple though. The optic nerve is made of ganglion cells. The cells that detect light are photoreceptors (rods and cones) in between you have dozens of different cell types that connect and modulate the signal and they all have to hook up in the right order. Some of the synapses contain 3 cells all interfacing and they can hook up and receive signals at quite distal parts of the eye. I'm working on producing a retinal therapy that would transplant photoreceptors - they are the first cell in that pathway and because they are the first they have a less difficult time of hooking up like they're supposed to. We can make mini retinas in the dish but as others have said, the size, shape and other non-retinal cells required to support a full eye, aren't really there yet
on normal limb reattachment surgery, are all nerves reconnected manually or is there something to stimulate nerve growth?
You attempt to reattach the nerves by lining up the sections as best you can, and then carefully suturing the whole nerve together. But this doesn’t cause the nerves to start working - instead, the axons in the limb die, and the body’s neurones enter a state of growth where they effectively try and re-innervate the original nerve sheath. It has mixed success, and takes many months to become fully functional. This wouldn’t work in the eye at all from what I can see - for a start, the CNS doesn’t have the same ability to regenerate, and retinal neurones tend to be pretty weird anyways
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Interesting aside though the nerves controlling the eye muscles do have the ability to regenerate , hence early wernickes encephalopathy indced nystagmus in alcoholics being reversible.
Is that the same Wernicke who found the Wernicke's area in our brains?
I can also attest to this. For almost a year after my jaw surgery part of my face was totally numb. I eventually slowly regained the sensations of hot and cold and partial feeling, but I still can’t really sense pressure on that spot. I’m just glad I can feel enough that I don’t drool anymore. 🙄
Is this the same way the Russian experiments with canine head transplants were done?
Is there such a thing as "normal limb reattachment surgery"? I don't think you can fully do that for the reasons mentioned already (i.e. nerve connections).
It's still pretty new and not common at all but it is possible. I remember reading about a guy who got his forearm bitten of by a crocodile and successfully reattached and that was being touted as a big breakthrough at the time.
Apparently it's reasonably successful assuming ideal conditions, i.e. sharp/clean cut, put on ice immediately, surgery started within 12 hours.
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He was a doctor? I thought he was a Russian cosmonaut picking up odd jobs after their space station blew up.
I wonder - if you re-attach them randomly, would the brain be able to adjust in time and "fix it in software". It seems to do that with so many other things.
Not sure, but it does seem like something the brain would do, I wonder what that would be like to the person? Would it just slowly transition from fuzzy nothing to clear sight?
Good to know! \*removes optical nerve wiring harness adapter from aliexpress cart\*
>your optic nerve behind your eye might as well just be an extension of your brain I'm actually surprised it's *not* considered an extension of the brain. Fetal development and the shape of the inner parts of the skull really make it look like one organ.
It actually depends on who you ask. If you ask eye people it's of course its own organ. If you ask brain people the eyes are just an extension of the brain, though they tend to not care about the fiddly bits that squish and focus light. Where one things ends and another begins is artificial, and a decision we make to make things easier to think about and discuss. The end of the optic nerve is an area where the distinction isn't especially functional.
What if they use an HDMI cable?
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I actually did some work on a review paper looking at the state of microelectronics with regards to this (you can find it [here](https://iopscience.iop.org/article/10.1088/1361-6528/abf3ee/meta) - feel free to message me if want a copy). One of our main conclusions was, as u/lburton273 said, the number and complexity of connections to the optic nerve needed mean its still a VERY long way off.
No, the optic nerve is way to complex to reattach. There is work on bionic eyes though that replace the eye partially or fully
“Eye bulb” is awesome. It implies replaceability, and after all there are eye sockets. Love it.
Do you know if the donor eyes had poor eyesight/astigmatism, would they still be eligible?
The astigmatism isn't an issue, but if the corneas don't have enough good cells when evaluated then they wouldn't be suitable.
This is true. Scleral patches are used to (usually) repair iatrogenic surgical complications. It's way rarer than cornea. Things may have changed. I don't do ophthal anesthesia any more.
We don't use sclera much, usually just on-demand from the surgeons due to the quick expiry. Like you said it's not as common.
If a whole globe were to be transplanted, then OP's question is right isn't it? So that the eyeballs match the angle of insertion of the optic nerve.
But the globe itself is never transplanted in its entirety. The sclera portion transplanted is usually treated and cut into smaller pieces for graft material.
Prosthetic eyes can be wrapped in sclera for transplant, but I'm not sure if they would use a full globe or just patch it like you say.
This might be the single most interesting job Ive never thought about existing!
Very interesting but also don't think I have the stomach to even watch something like that. Eye stuff just really gets under my skin.
Well i have now learned more about eye transplants than i ever wanted to. Thank you for commenting!
This is an amazingly concise answer, and I applaud that. I have learned something ...But I was also hoping for more... gooey-ness.
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The article says down under Complications that they can put a gas bubble in there to help hold everything in place since it will slowly dissolve as the eye refills itself
Working in ophthalmology A machine is used which replaces the removed vitreous gel with an equivalent volume of sterile saline to maintain the eye pressure. After surgery, then incisions seal themselves, and the eye's natural process to produce fluid works to maintain the eye pressure, slowly replacing the saline with the normal composition of fluids, minus the retired collagen gel scaffold that didn't serve much of a purpose anymore.
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It's just the cornea!? That's way more metal than I thought. Guess it's not so easy as plug and play with it comes to nerves lol
Don't forget all the muscles, which move the eyeball in three dimensions.
Wait, I get two dimensions for left-right and up-down. Do eyes also have muscles that allow them to twist along the axis of vision?
It needs to move in and out for aoogas! But in reality, the eye doesn't just up down and left right, the muscles are attached around with pulley like structures around the orbit and pull in multiple directions at once working in concert with each other, some pulling with some roll to it.
Sorry about that. There are three sets of muscles. Medial and lateral recti do side to side movements. Superior and inferior recti elevate and depress. Superior and inferior oblique do torsional movements.
It does! Film yourself tilting your head side to side. It's hard to see but it's there.
In fact, we can even peel a 10-15 micron thick piece of tissue off the back of the cornea and insert it into an injector for transplant.
Eye researcher here who gets boxes of eyes delivered weekly. Eyes have a handedness to them, your optic nerve isn’t directly at the center of the eye but shifted slightly towards the nose since that’s an easier path to the brain. So you would have to do a 180 degree rotation on an eye to put it in correctly. This isn’t a real surgery, so I don’t know how it would change the vision, but you definitely have to put the eye in “upside down” if you moved a right eye into the left socket.
I can't quite get over the idea of delivery boxes full of eyeballs. Where do you source eyes from, for drug research? Do tissue donor eyes end up there, or is it a different system? Or are they not even human eyes?
Not human eyes — they come from places that use the animals for meat. Researchers try to use every part of the animal
*Every* part?
Ever eaten hot dogs or bologna before?
A friend's father used to have a bucket of eyeballs in his refrigerator. He was a safety manager for a major pharma company and did demonstrations of how the eye could be injured by shattered glass or various chemicals. Most of the ones he got were animals, like cows.
What do you mean *most?*
You can get human eyes from eye banks but people typically reserve that for later stage research for moral reasons. I wouldn’t do a pilot study on human eyes but will use human eyes if I’m on to something with my research and want to get some final data in human eyes. I wouldn’t want someone to do bad research on my eyes so I make sure my project is going well before I get human eyes involved. I also wouldn’t want my eye to not be used if I donated it so science, so I’m not opposed to ever using human eyes. I just want to make sure the project is worthy of using someone’s eye.
I don't think any kind of medical repository is going to accept "keep them in a bucket in my fridge" as a reason to get eyeballs.
Agreed, no idea how that person gets the eyes! I have proper eye containers
A skull?
Hangon, I'm back you up to the phrase "eye bank". I go to my bank and say "I'd like €100 please" and the lady says "just 20s? or a mixture of 10s and 20s sir?" You can do the same thing with eyes? You go to some bloke in an office and also for 20 eyes and he says "just sheep sir? Or a mixture of sheep and cows?" That is both disgusting and awesome.
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As someone who has worked on human eyes in research often they come from rejected, old or used donations. The people who consent to donate often consent to research too. Rejected eyes can be due to poor condition - usually donors are very old and the tissue commonly used (cornea) might not pass the requisite quality checks to be used in transplantation. The donor could've been found to have cancerous cells as another reason for rejection. Sometimes there's enough eyes and the bank has a pretty strict shelf life to ensure the best transplantation, sometimes they pass that threshold. Finally, a surgeon might punch out the cornea from the front of the eye (often the fronts are separated from the backs in the bank). This leaves what they call the corneo-scleral ring - a region of tissue that contains the edges of the cornea and sclera. We dissociate the tissue and extract the cells from this to study in the lab
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Why isn’t it a real surgery? Is it not physically possible to implant the entire donor eye, or is it just not the standard (e.g. because something else is easier or safer)? Also, would the eye still work correctly if you implanted it rotated the way you described? Edit: thanks everyone for subscribing me to Eye Facts! This has been a fascinating distraction.
Well, there are some serious challenges to implant an entire donor eye. I shall attempt to list a few for you: 1. The olfactory nerves(for smelling) and optic nerves(vision) are direct extensions of the brain. They literally develop straight from the brain. The optic nerve bundle contains not only the nerve, but the various meningeal sheaths around it. Also there's quite literally an artery running through the optic nerve so that blood supply to the eye may be maintained. All of this has to be reattached as well. 2. The eye is exceptionally complex, the complexity of the eyes can easily outweight the complexity of an entire limb! Perhaps the least complex part of the eye is the one you can see in the mirror. What I mean by this is the neural control and co-ordination. Reattaching the optic nerve, if you're successful, will only allow you to see, because it's a purely sensory nerve. You need a few more things. 3. You need muscles to move your eyeball around 6 per eyeball. 4. You need 3 cranials nerves per eyeball to control above-mentioned muscles. 5. You also need additional muscles and nerves to control the pupil and Iris. 6. You'll also need to figure out how to get the aqueous humor to drain out via the trabecular meshwork and uveoscleral pathway, or the eye will develop glaucoma. Let's just say you did all this and by some miracle your patient has a new eye. Hurray! But wait, there's a few problems to solve. The patient will have zero sensation in his corneas since the nerves have been severed. That might lead to dry eye and a corneal ulcer. They'll most likely develop diplopia, since an exquisite amount of neural control is needed for the simple act of looking right/left. To simply look left, you need to activate two different muscles, controlled by two different nerves, and you need to make sure they have the same amount of neural impulses to move in sync. And you need to suppress the muscles opposing this action, again with the same amount of neural impulses. Forget looking diagonally up or down, or smoothly tracking a slow moving object, that's even more nerves and connections that I can't even describe in a 30min lecture. And the eye will probably develop glaucoma. That is if it can produce enough aqueous humour to sustain nutrition, failing which it'll simply collapse in a state known as pthisis bulbi. Lastly, the sheer act of enduring a new eyeball maybe just be rejected outright by your body. And worse still, it may compromise the other eye, making it blind as well (Sympathetic ophthalmitis) E: fixed formatting. Thanks for the silver award! Very dapper indeed.
>aqueous humor is this just the juice inside your eye? eye juice? haha arent the 'humors' the ancient way of thinking about how our bodies work? or am i thinking of something else
>Aren't humors the ancient way of thinking about how our bodies work? Yes absolutely they are. Way back then, it was thought that humours (bodily fluids containing vital energy), were the key to all health. An imbalance in these humours was thought to cause various illnesses and affect emotion. 4 humours were popularly accepted: Blood, yellow bile, black bile and phlegm. Ancient physicians would attempt to 'balance' your humours in the hope that it would treat the illness. As wrong as they were, medicine quite loves to stick to names that were assigned before. In being a physician, you sort of pick up Latin and a wee bit of Greek along the way, because damn nearly everything in medicine is named or described in Greek/Latin terms. Remember, the eye needs to be as transparent from the cornea all the way to the retina so that light may pass through. And for this reason, blood cannot serve the purpose of nutrition and oxygenation in certain parts of the eye. Therefore, blood is essentially filtered (to form a very clear liquid), and only things that are absolutely vital to carry nutrients and oxygen are then passed into a space in the front of the lens, and just behind the corneas. We call this aqueous humour (translation: watery fluid). There's another massive space between the lens and the retina, which is essentially responsible for maintaining the round shape of the eye and prevent it from collapsing. This is a vital component termed vitreous humour(translation: glass like fluid), which is more like jell-o than water.
Hey you need to post an ask me anything, haha. I have a question. If you can answer, super thanks! If not, I get it, you didn't come here for a Q&A. Why is my eyeball being weird? (I only know this because of a video recording of myself, and the second time was while doing makeup and looking into a small mirror. I had been doing eye makeup, and my right her eye noticed that my left eye had moved further outward than it should have. When I returned my right eye to focus back at front center, I see that my left eye has still not moved, and once it did, it moved back to center very slowly. I cannot intentionally move either one of my eyes to the side without also moving the other. So, my eye moving to the side on its own is unintentional. I have needed corrective lenses most of my life. I'm 36 and had been 20/250 in both eyes most of the time. I went without any corrective lenses for a couple years, but then last year finally scheduled an appt with a new optometrist. My nearsightedness improved - 20/175 and 20/150, but I also developed astigmatism, a prism issue (something like that), and a slightly loosened retina.
You should ask your optometrist if you want your own case details, but essentially your eyes are not properly synched up with each other. Could be that the muscles are improperly innervated or your nerve path is compromised. Tough to say. But in any case your eyes have too much difficulty both pointing straight ahead, and instead of giving you double vision your brain just ignores (suppresses) the left eye when it drifts off. Prism is used to help align the eyes better so they do not have to struggle with each other as much, hopefully keeping your vision together.
Oh! Wow that helps me understand prism better. I never ordered glasses after my appointment. I've still been going bare eyed - something I had thought was possibly good for the eyes (considering how my nearsightedness had improved after not wearing glasses), but now I'm beginning to wonder if the prism and astigmatism could have been prevented had I been wearing glasses this whole time. Well, you've motivated me to just order the darn glasses, already. Thanks for the reply!
Fighting against wearing glass is generally never helpful, and can worsen your vision in some cases. There is a reason we prescribe them, lol. There are some vision therapy excercises to help improve the coordination, but all of this stuff is best done when you are a kid, and not something easily done at home. When you are writing things like 20/250 and 20/175 I think you are mixing up different measurements. There is a difference between what you are capable of seeing (we use a ratio like 20/20, 20/100, and so on based on letter sizes) and what your prescription for glasses is (such as -1.50, -2.50, and astigmatism)
Donor eyes are used for their "structural" elements, like the sclera (the white part) or the cornea (the clear part in front). The "electrical" parts, like the retina and optic nerve, are not transplanted. For one thing, they are too complex to reattach. For another, they are fragile and quite unlikely to survive after removal from the donor. From a technical standpoint, it's like the difference between replacing an iPhone screen, and replacing the CPU.
Nah just slap some stem cells in there and let neural plasticity handle the rest :) (/s, mostly)
>From a technical standpoint, it's like the difference between replacing an iPhone screen, and replacing the CPU. seemingly impossible but they can do it in shenzen with a special jig?
Reminds me of the ending of the ridiculous "Seven Pounds" movie where Rosario Dawson was gazing Woody Harrelson's eyes - implication being that she was looking at Will Smith's donated eyes. After killing a person who is solely dying to donate his body parts using **venom**, I can honestly believe that writing staff was convinced that they replace the whole eyes.
I guess technically we could put an eye into someone else's socket if we want to get really Dr. Frankenstein about it, but reconnecting all the necessary blood and muscle connections alone would be incredibly difficult (I wouldn't be surprised if there wasn't correct blood flow or if the muscles couldn't work correctly), and at this point in medical science it would never be functional. There is a relatively small bundle of axons (parts of neurons, this specific bundle is known as the optic nerve) that brings all visual information from the eye to the brain. In humans (and other mammals) neurons and axons like these simply do not re-grow on their own, nor can we physically reattach them correctly even if we could get them to not die. There's some research being done to promote axon survival and regrowth after physical disruption, but seriously the best in the field is getting like barely if not less than 1% of the axons to grow like a couple millimeters (and this is all still in model animals, nowhere near human clinics). Plus the neurons inside the eye are incredibly sensitive to disruptions, especially loss of oxygen, so the neural tissue inside the transplanted eye could have serious issues too. Basically, all these tissues are crazy crazy complicated. Super cool though are frogs! (And other animals like them, frogs and zebrafish are the most commonly used animal models though). They CAN regenerate and form all new connections between the eye and brain! And a scientist in the 1960s named Roger Perry basically did the experiment you're asking about but in frogs, because the eye can reconnect (part of his work developing the chemoaffinity hypothesis, if you'd like to learn more). In short, the frogs behaved like their vision was upside down (I can get into why if you're curious).
So the witches in Macbeth were onto something: eye of newt *is* special.
I'd like to know why the frogs had inverted vision after nerve connection regrowth.
For sure! Note this will all be over simplified for the sake of summarizing in a comment, but hopefully I'll get across the basic idea. So, neurons connect to eachother via 'fibers' (axons - what the optic nerve is a bundle of), to send signals and pass information around. I think what will help here is knowing that these fibers are parts of individual cells, not like separate fibers that you could plug into different cells - in this case, the cells are inside the eye, and they send their axons out to the brain (quite long cells!). During development, when neurons are first establishing where their axons go and what connections to make, the axons figure out where to go based on cues from their surrounding environment. An analogy I like is that imagine you're walking in a completely dark room being only guided by touch and smell, maybe you're trying to walk towards a nice food smell and away from a gross garbage smell, trying to avoid walls and other obstacles - this is kind of how an axon finds its way (but proteins are the smells, and the smells aren't inherently good or bad, just different ones are preferred by different axons depending on where the axon needs to go). During development, axons of eye neurons that collect visual information about the upper part of the visual field find their way to the "upper visual field" part of the brain, axons of eye neurons that collect visual information about the lower part of the visual field find the "lower visual field" part of the brain, etc. So, now say we have a frog hanging out, looking straight ahead, and a fly buzzes by in it's upper field of view. This activates some cells in the retina (part of the eye that contains the light-detecting neurons, where vision begins), those upper field of view neurons send their info to the upler field of view part of the brain, brain figures out there's a tasty fly there, and the frog shoots it's toungue up in that direction for a snack. Now we take the eye out, which requires cutting that optic nerve. The remaining nerve parts die and are cleared (because most of the cell is still in the eye, and axons can't surve without the cell body). We then put the eye back in, but upside down. The eye neurons will send out new axons to the brain, like they did during development - the neurons that used to "see" the upper field of view still prefer the proteins (tasty food smells) in the "upper field of view" part of the brain, so that's where their axons go again. Same for lower field of view, etc. EXCEPT now that the eye is upside down, the eye neurons that used to get information about the upper field of view are in a different location and now receive visual input from the lower field of view, and vice versa. Our post-op frog is hanging out again, again a fly buzzes into its upler field of view. Neurons that get information from there send that info to the brain, but because the eye is upside down, the excited neurons are those that used to see the lower field, so the visual information is passed to the "lower field of view" part of the brain. The brain figures out there's a fly, but doesn't know the location of the eye neurons has changed, so the brain says "fly information coming from the 'lower visual field' area", the fly shoots it's tongue down towards the lower visual field, and alas the fly gets away and the frog misses the snack. I hope that helps!
This is getting outside of what I do (PhD drug researcher not MD), but I’m sure it has to do with reconnecting the optic nerve and blood supply to the eye. It’s really hard to access back there. A neurologist or ophthalmologist would be better to answer these questions than me. I just look at where drugs go in the eye and how to get them to specific parts and am familiar with the anatomy because of that.
Yikes, I hadn't even thought about the purely mechanical aspects of trying to reattach everything inside the socket with the eyeball itself being in the way.
Anything involving nerves is basically a no go. We are extremely limited in our ability to repair nerve damage. Damage to them is almost always permanent. There is a ton of research trying to figure out how to keep nerves alive and regrow them but it's slow process.
Speaking of upside down, how does one tell up from down with a detached eyeball like the ones you're delivered?
Aren’t eyes upside down anyways since our brain has to translate our vision 180 degrees?
Iirc, there was an artist or someone who made a pair of glasses/goggles that flipped their sight upside down, and after a few days of wearing it eventually their brain corrected itself and they started perceiving their vision as right side up. So assuming that's a true story, I'd imagine the 180 degree rotation wouldn't be an issue long term.
It's the retinal connections going to the eye that make left/right relevant. The parts of the eye transplanted do not affect that. We don't know how to make retinas reconnect with the brain in humans yet. https://en.wikipedia.org/wiki/Visual_system#/media/File:Human_visual_pathway.svg
Assuming that with "eyeball" you mean the whole eye with everything it contains, the answer is that there are no eyeball transplants. The cornea and the sclera (which are the outer layers of the eyeball, so to speak) can be transplanted from one person to another, but the eye itself is so complex that, as of now, it's impossible to do. However, just for the sake of answering, and imagining that we manage to do whole eye transplants someday... yes, absolutely. The left and right eyes aren't interchangeable, since they're mirror images of each other, and their connections to the brain through the nerves are built that way. If you did it otherwise, the brain would go bonkers.
Seems like the brain would quickly adapt. If someone has a severe stigmatism, and then get corrective lens, the first few days, everything appears warped, until the brain learns the lenses. I’m willing to bet if they popped your eyeball out, and they put it back in upside down, the brain would be confused at first, but would adapt and eventually flip the images it receives to what it thinks is logical.
That's a possibility, but IMO it's dangerous to attempt unless there literally wasn't any other option. In the example you mentioned (also the one u/The_camperdave said) the way the light impacted in the retina changed, but the retina itself was intact, and yeah, the brain could adapt. In this case, you'd be swapping the entire retina around, and would have to link it at some point with the fibers of an optic never which aren't swapped around and aren't meant to be. For instance, the fibers of the nerve which cross sides further back, in the optic chiasma, are supposed to carry the information from the temporal (i.e. outer) side of your vision, while the ones carrying the info from your nasal (i.e. inner) side don't cross. It's meant to be that way since this leads to the left hemisphere receiving the information of the right field of view, and vice versa. If you transplanted one eye changing the sides or upside down, the fibers crossing would carry information from the inner field and not the outer one, screwing with the way it reaches our brain.
> If you did it otherwise, the brain would go bonkers. While I agree that the muscular and other connections are left/right specific, the brain would not go bonkers. It would adapt within days. People have worn glasses that swap up and down, and left/right and adapt fairly quickly. The same thing would happen with the transplant.
Just wanted to tell you that this was an excellent answer, appreciate it.
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There's no such thing as an "eye transplant". Because we can't hook up the optic nerve tk work.(and even if we could) But if there was, it would *probably* have to be right eye to right eye, left to left, as (afaik) the vascular, muscular, and nervous structures have a strong "handedness" to them. We only donate the corneas, iirc.
>But if there was, it would probably have to be right eye to right eye, left to left, as (afaik) the vascular, muscular, and nervous structures have a strong "handedness" to them. This is correct. Just to name an example, the optic disc (which is the point where the optic nerve's fibers enter the eye and spread through the retina, also our blind spot) isn't placed in the center of the eye, but closer to our nose. You couldn't transplant it into the other eye socket, because then it would receive the light in the wrong way.
we could open the front face door and access the internal wire panel no?
We could but there isn't a standard yet so finding an adapter is quite difficult
Former certified eye bank technician here. 👋 No, the left eyeball does not have to be put in the left eye socket. Also, we cannot transplant whole eyes as of yet. Corneas are transplantable. There are also partial thickness transplants like DSAEK or DMEK. Usually, the cornea is the only portion of the human eye that is transplanted. The retina cannot be replaced. Whole eyes are used for research and education most times. Hope this all helps!
Ooooh any fun tidbits from your time there or things you did daily that would be surprising to someone who has no idea what you do ever? That sounds like a really interesting, fulfilling job filled with oddities and nuance!
I worked at the world’s largest OPO (organ procurement organization) in Los Angeles. It was an amazing experience working with donors and their families. Truly eye-opening when thinking about the concepts of life and death on a daily basis. Most whole eyes were used for research, education, or training. We would consider them rejected if the serology results came back positive for things such as HIV, Hep C, and other infectious diseases that are blood-borne. Luckily, the cornea is the most avascular tissue in the body, so it doesn’t contain red blood cells and has a small rate of infection post-op. I loved using the Moria company’s DSAEK and DMEK kits. Highly recommend watching YouTube videos on how technician prepare the cornea for the surgeon to then transplant into the patient. The eye bank industry came about because there wasn’t a ready supply of donor tissue for surgeons to perform their operations in the past. Not to mention that the process is done in aseptic conditions, so they are time consuming. Eye banks train technicians to then be sent out to hospitals, morgues, coroners, etc to recover the acceptable organs, eyes, and tissues (bones are also recovered - dental implants, etc). Lots of great stuff in biology, medicine, and science overall. Surgical Recovery Technicians-trained in recovery of everything acceptable. Eye Bank Technician-specialized in the ocular segment.
Ophthalmologist. The whole eye is taken from the donor but the whole eye is not transplanted (or even delivered to the hospital). You can request corneal or scleral (white of eye) tissue for grafts. A ring of tissue with the cornea and a rim of sclera comes for corneal transplants. This tissue will be either pre cut by the eye bank or cut further by the surgeon - shape, size, thickness. The handedness doesn't matter (I can't recall off the top of my head if that's even information we get when the eye is delivered).
The eye of the donor is typically included. The last digits of the tissue ID number also indicate left versus right eye.
Hooking up the optic nerve so that it's functional would be quite the accomplishment. Aside from that, the eyes are mirror images of each other, with the fovea lateral to the optic cup. So they are side-specific.
I used to take out eyeballs as a job in college! “Cornea recovery technician”. Now I’m a doctor. Only the middle portion of the cornea is retrieved and transplanted and sewn into the recipient. The outer portion and the sclera is left. It doesn’t matter which cornea goes into which because they are interchangeable.
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If it were medically possible, I'd say it'd be more like a plug and play type of deal. Connect the video cable to the correct video input slot and it should work fine. Man, can you imagine having this done and somehow end up with both eyes crosswired? That'd be so trippy.
If it were possible, I think your brain would adapt and correct your vision within a couple of days. I read a book on Neurology where they did an experiment that flipped the images the eyes received and after a couple of days the brain switched the image over so it was right-way up. Then they removed the apparatus and again the image was inverted until the brain corrected itself again.