This one didn't win the poll, but someone specifically asked for this topic, so I'll write about it anyways. Also, as someone who is working towards being a trauma surgeon, this is a topic I'm really passionate about.
So, I think a lot of people have a misconception about whether or not it is possible to transplant eyes. We transplant a lot of other stuff, so why not eyes? Well, you can transplant pieces of the eye, like the cornea, the clear part at the front of your eye (which is avascular). You can also replace the lens with an artificial one (the lens is also avascular). This is how you can fix cataracts, just taking out the old shitty lens and putting in a clear new one. That procedure can be done in a clinic in like thirty minutes (which is fuckin crazy if you ask me).
But what we're talking about here is taking out the entire eyeball and replacing it with a donor eye. It sounds cool as hell, so why is it so hard? First off, the eye is a part of the central nervous system (the first two cranial nerves, are in fact part of the CNS, not the PNS). So the optic nerve (CN II) is what carries special sensory information to the dorsal brain (occipital lobe). To control eye movement, you have CN III, IV, and VI (oculomotor, trochlear, and abducens nerves). The oculomotor nerve controls eye movement, pupil constriction, and the upper eyelid. The trochlear nerve controls movement of the eye downwards, outwards, or to the nose. The abducens nerve moves the eye outwards. Several other nerves are involved in keeping the gaze level with movement, visual tracking, and parasympathetic/sympathetic functions (rest and digest vs. fight or flight). The point is, eye nerves are complicated as hell.
The blood flow to parts of the eye is also very complicated, and is very difficult to properly reattach for full perfusion (esp the retina).
Now, onto the good parts. So the eye is what is called "immune privileged." This means it has protections against the immune function of the body (to avoid autoimmune attacks). The eye has no lymphatics, few immune cells, and immune suppressing chemicals. This makes it a great place for implants, as it is unlikely that the body will attack the foreign tissue (stem cell implants are becoming more common).
The first whole eye transplant was done about a year ago (November 2023), and so far the eye is still there with adequate blood flow. However, the guy can't actually see out of it. The surgery took 21 hours and involved a huge team of some of the best surgeons in the world. It was not an easy thing to do. They also implanted some stem cells with the optic tract in hopes to regenerate it, but that still hasn't restored vision in the eye. So, while this case is a major win in the area of eye transplants, there is still a ways to go.
So why do we even need to do so many eye transplants? Well, all kinds of things can lead to the loss of the eye, whether it be disease or trauma. Surgeons try very hard to keep the eyes in a patient, but that isn't always possible. Sometimes the tissue is too destroyed for repair or the damage causes permanent pain. Enucleation is the removal of the eye. Usually, as much of the optic nerve is left as possible, as well as the musculature. Possible options after healing include fake eyes (like glass ones), which can be crazy realistic and can be moved with the eye muscles.
I hope this was an interesting read, and thanks for reading my ramblings. I didn't feel like the typical post format would work for this one, and I like to imagine it like a bonus since it didn't win the poll, lol.
