Eyes

Wonder if there are any medical / biology students or even doctors on here.
I was wondering that, if someone has 3 eyelids- meaning outer eyelid, than a membrane and then the eyeball itself.
What would be the significance if such a membrane is indeed present is some human eyes?
Thanks in advance for your feedback

a reply to: Hyperboles

They're probably amphibious aliens. That's my expert opinion.

a reply to: NarcolepticBuddha

Is that your final answer?

originally posted by: Hyperboles
Wonder if there are any medical / biology students or even doctors on here.
I was wondering that, if someone has 3 eyelids- meaning outer eyelid, than a membrane and then the eyeball itself.
What would be the significance if such a membrane is indeed present is some human eyes?
Thanks in advance for your feedback

The vestigal remnant of a third eyelid or nictitating membrane is present in all humans, and is called the Plica semilunaris of conjunctiva.

Only one known primate has a functioning third eyelid, the Calabar angwantibo.

originally posted by: Arbitrageur

originally posted by: Hyperboles
Wonder if there are any medical / biology students or even doctors on here.
I was wondering that, if someone has 3 eyelids- meaning outer eyelid, than a membrane and then the eyeball itself.
What would be the significance if such a membrane is indeed present is some human eyes?
Thanks in advance for your feedback

The vestigal remnant of a third eyelid or nictitating membrane is present in all humans, and is called the Plica semilunaris of conjunctiva.

Only one known primate has a functioning third eyelid, the Calabar angwantibo.

Ummm...you just made that up...right...

Riiiight...





YouSir

originally posted by: YouSir

originally posted by: Arbitrageur

originally posted by: Hyperboles
Wonder if there are any medical / biology students or even doctors on here.
I was wondering that, if someone has 3 eyelids- meaning outer eyelid, than a membrane and then the eyeball itself.
What would be the significance if such a membrane is indeed present is some human eyes?
Thanks in advance for your feedback

The vestigal remnant of a third eyelid or nictitating membrane is present in all humans, and is called the Plica semilunaris of conjunctiva.

Only one known primate has a functioning third eyelid, the Calabar angwantibo.

Ummm...you just made that up...right...

Riiiight...

YouSir

It is real

originally posted by: YouSir
Ummm...you just made that up...right...

Riiiight...

I admit to being a fan of made-up names like the turbo encabulator or the name Marko Rodin and his protege gave to the fictitious device that will produce unlimited energy, allow travel anywhere in the universe, and cure all disease, the "flux thruster atom pulsar electrical venturi spacetime implosion field generator coil". He may be slightly megalomaniacally insane to make such claims, but he sure knows how to make up a name, I give him credit for that.

In this case though, I didn't make any of that up. Humans do have a vestigal remnant, but it would take a genetic or developmental abnormality for such a vestigal remnant to manifest. When the human fetus is developing, the growth of the nictitating membrane doesn't keep up with the growth of the rest of the eye so that's why it ends up being a remnant. However in exactly two humans that we have records of, the nictitating membrane growth apparently did keep up with the rest of the eye to a very significant extent, so to say it's extremely rare would be an understatement.

In the second case, the nictitating membrane was surgically removed, but she still couldn't see out of that eye after that surgery which the doctor attributed to deep amblyopia.

Persistent unilateral nictitating membrane in a 9-year-old girl: A rare case report

After a thorough literature search, this is only the second such case report of a persisting nictitating membrane in a human being.

In a handful of other people, the fetal nictitating membrane development didn't keep up with the eye but did develop slightly more than the usual vestigal remnant.

originally posted by: NarcolepticBuddha
a reply to: Hyperboles

They're probably amphibious aliens. That's my expert opinion.

Lol nice one

originally posted by: Arbitrageur

originally posted by: Hyperboles
Wonder if there are any medical / biology students or even doctors on here.
I was wondering that, if someone has 3 eyelids- meaning outer eyelid, than a membrane and then the eyeball itself.
What would be the significance if such a membrane is indeed present is some human eyes?
Thanks in advance for your feedback

The vestigal remnant of a third eyelid or nictitating membrane is present in all humans, and is called the Plica semilunaris of conjunctiva.

Only one known primate has a functioning third eyelid, the Calabar angwantibo.

Ok thanks.
So, in the case of only a remnant of the membrane, how would a vitamin A deficiency become apparent when looking into the eyes?

originally posted by: Hyperboles
So, in the case of only a remnant of the membrane, how would a vitamin A deficiency become apparent when looking into the eyes?

Vitamin A deficiency would have mostly the same symptoms regardless of development of the nicitating membrane, although one of the symptoms is corneal xerosis or excessive dryness of the cornea, which is bad in any case, but if the nicitating membrane is more developed it might be even worse. Vitamin A deficiency is a leading cause of blindness and it happens a lot in some poorly developed countries in Africa.

This source has some pictures of vitamin A deficiency symptoms, but don't open it if you have a weak stomach, they are very graphic.

Could it be that if someone is very sensitive to light from birth, this membrane stays intact? and the person is still sensitive to light

originally posted by: Hyperboles
Could it be that if someone is very sensitive to light from birth, this membrane stays intact? and the person is still sensitive to light

We can't infer any statistical pattern from a less than a one in a billion anomaly, there aren't enough cases for statistics.

However we do have a rather thorough report of the 9 year old girl and the investigations that were conducted in that case. There was no mention of light sensitivity in that report. In her case it doesn't make much sense to ask the question as you phrased it because the developmental anomaly occurred in the fetal stage, before birth, where there's not much exposure to light, and further it only happened in one eye and not the other which was completely normal.

The doctors also explained the investigations they conducted (biopsies etc) to look for other possible causes. They also asked if any relatives were known to have anything similar and the mother and father didn't know of anything so they didn't find any obvious genetic cause, and environmental causes can also be deemed unlikely since nobody else in the same environment experienced anything similar.

They also performed examinations of both eyes which were normal except one of them had the third eyelid, so if it was light sensitivity why would one eye have it and the other eye not? It's easier to explain as a developmental abnormality in the developing fetus.

Could another very rare case have a different cause? Sure but the doctors didn't mention any known cases of the third eyelid appearing after birth, so if all known cases started developing in the fetus where exposure to light is minimal there doesn't seem to be much reason to put that on your list of considerations.

Also typically, in terms of light sensitivity, anything that stands as a barrier or chance to reduce the number of photons getting to the retina, would in effect reduce 'sensitivity'

If you are thinking of some form night sensitivity for example, this wouldn't work like wearing sunglasses to prevent bleaching unless you can actually remove it to gain back those lost photons.

originally posted by: ErosA433
Also typically, in terms of light sensitivity, anything that stands as a barrier or chance to reduce the number of photons getting to the retina, would in effect reduce 'sensitivity'

If you are thinking of some form night sensitivity for example, this wouldn't work like wearing sunglasses to prevent bleaching unless you can actually remove it to gain back those lost photons.

Thanks Arb and Eros.
I actually have this membrane in both eyes and often get asked where do you come from. And one of the doctors while conducting my aviation medical seemed petrified of my eyes and I cannot bring myself to look into my own eyes in the mirror. heart sort of skips a beat.
Yes I am sensitive to white light or other bright lights including sunlight.

a reply to: Hyperboles
A number of different things can cause light sensitivity. A lot of people get more sensitive to bright light as they get older, but there are many things that can cause this sensitivity in people of all ages. Some of them can be treated. I doubt the light sensitivity is related to your membranes though.

The proper place to get medical advice is from a doctor who can look for causes of your sensitivity to light and see if they can be treated, and tell you about surgical options for the membranes. We already know the 9 year old girl had her membrane surgically removed so that's a possibility, but you have to balance that against the risks that go with any surgery. If it was me I'd probably try to live with them, but if I had to have surgery, I'd only get one eye done at a time because I can live with the risk of losing sight in one eye but not both of them. I don't know the requirements for passing the aviation medical, you might need vision in both eyes to pass that. If you have a good surgeon you shouldn't lose your vision, but there's always a risk of complications with surgery, even if it's a low risk.

a reply to: Arbitrageur

Thanks. vision is fine for class 1 aviation medical. It actually doesn't bother me to retain these membranes in both the eyes