Want help from an optometristudent? ask me in this thread

cool!

Are there any long term problems with eye surgery? I heard we have no proof of it as they are ¨too new¨ to have evidence

At what distance is the nodal point in the eye from the retina and from the surface of the cornea, considering a standard 24mm human eye ?

"Frito" wrote:
cool!

Are there any long term problems with eye surgery? I heard we have no proof of it as they are ¨too new¨ to have evidence

it depends what kind of eye surgery you are having. but i cannot say much about that since i am not an eye doctor. but they should be relative safe in the modern days. if you have some more options you should contact an eye doctor

"Fredz" wrote:
At what distance is the nodal point in the eye from the retina and from the surface of the cornea, considering a standard 24mm human eye ?

standard eye is 22.22mm and has 60 dioptries strength. You mean from that point where the eye starts to converge? where light becomes infinite? i am not able to look up at nodal points at the moment, but can in a day or two if i didn't answer you correctly now

ah i understand what you meant now..what the distance is from the retina to the corneas nodal point.. i have numbers on that in my books, but i do not remember them correctly now. have to look them up. but since the whole human eye in a standard human..the eyeball is 22.22mm from the back to the front..so in this case the nodal point is 22.22mm from your retina. but remember all eyes have different values, yours might be 24mm or 20mm.

"Qosmius" wrote:
standard eye is 22.22mm and has 60 dioptries strength.

These values come from the Emsley standard reduced 60-diopter eye, which is the simplest model of the eye and is often used in ophthalmic education, but it doesn't have the size of a real human eye.

I already know the position of the nodal point in this model (16.67mm from retina) and in the Listing schematic eye model (17.2mm from retina, with a 22.9mm distance from cornea to retina).

Emsley eye model



Listing eye model



What I'm after is the position of the center of perspective in a standard human eye, which according to what I've read (and hopefully understood) coincides with the position of the nodal point (the point at which a ray is not deviated), contrary to what happens in photography.

in a human eye the light will always be bent. because the mass of the eye is greater than N=1.0 also there is several nodal points in the eye.

i find it hard to fully understand your question. if you mean the distance where the light comes from infinity or as you can say " unbent " light is over 6 meters. do you want to calculate this so that unbent light comes from lets say 20 cm which is how far away the oculus is?

also that nodal point 16,16mm you are talking about, is not to cornea..it is either the front or the back surface of the lens

if this is not good enough pls try to write the question as accurate as you can and be sure to know exactly what you are looking for.. and i will look it up tomorrow. goodnight

"Qosmius" wrote:
in a human eye the light will always be bent.

Yes I know that, it's somewhat illustrated by this schema :

Le Grand.png
But there is also a theoretical point in the eye for which rays passing through it are not deviated, and that's the nodal point in reduced eye models, as illustrated by this schema and explained in the links I posted :

nodal_point.png
What I wanted to know was if there was another reduced eye model also using a single nodal point, but based on the size of a standard human eye. Because both Listing and Emsley models use sizes that don't correspond to in-vivo values, resp. 22.22 mm and 22.9 mm from the front surface of the cornea to the retina, when this value is 24 mm in a standard human eye.

"Qosmius" wrote:
also there is several nodal points in the eye.

The human eye doesn't have any nodal points per se, it's only a characteristic of eye models that are approximating its inner workings. There are two nodal points in schematic models of the eye (Gullstrand, Le Grand), but there is only one nodal point in reduced eye models (Listing, Emsley, Donder).

"Fredz" wrote:

"Qosmius" wrote:
in a human eye the light will always be bent.

Yes I know that, it's somewhat illustrated by this schema :

Le Grand.png
But there is also a theoretical point in the eye for which rays passing through it are not deviated, and that's the nodal point in reduced eye models, as illustrated by this schema and explained in the links I posted :

nodal_point.png
What I wanted to know was if there was another reduced eye model also using a single nodal point, but based on the size of a standard human eye. Because both Listing and Emsley models use sizes that don't correspond to in-vivo values, resp. 22.22 mm and 22.9 mm from the front surface of the cornea to the retina, when this value is 24 mm in a standard human eye.

"Qosmius" wrote:
also there is several nodal points in the eye.

The human eye doesn't have any nodal points per se, it's only a characteristic of eye models that are approximating its inner workings. There are two nodal points in schematic models of the eye (Gullstrand, Le Grand), but there is only one nodal point in reduced eye models (Listing, Emsley, Donder).

you seem to answer yourself in another question..if you already have a model that uses 1 nodalpoint just use that one :P i do not know if there are more reduced eye models, atleast we havent learnt anymore than 3 standard models that is widely known, there is no point in knowing more than them. a standard human eye is used to make theorethical numbers out of them..you cannot use them in real life because all eyes are different. a nodal point is where the light gets refracted..a human eye has 6 of them ..front of cornea, back of cornea, front chamber, front and back of lens and vitreous chamber.

if you want to know more about reduced eye models maybe you should talk to someone who is taking a master or doctor since those are mostly used for science i believe, they have not much practical use

what are you going to use those numbers for anyways?

"Qosmius" wrote:
you seem to answer yourself in another question..if you already have a model that uses 1 nodalpoint just use that one :P

As I've already said in my previous messages, I want to find a model that uses the real size of the human eye, not a reduced model with a non-realistic size. I don't know if such a model does exist though, I guess not considering your answers and what I've read so far.

"Qosmius" wrote:
i do not know if there are more reduced eye models, atleast we havent learnt anymore than 3 standard models that is widely known, there is no point in knowing more than them

Yes, I can understand that it would be a waste of time for an optometrist. I did find several references to other schematic and reduced eye models but they're in research papers and behind paywalls unfortunately.

"Qosmius" wrote:
if you want to know more about reduced eye models maybe you should talk to someone who is taking a master or doctor since those are mostly used for science i believe, they have not much practical use

Yes that would probably be the best route I guess, your help has been useful though, thanks.

"Qosmius" wrote:
what are you going to use those numbers for anyways?

At first it was only to be able to calculate the FOV more exactly in DIY HMDs and to design algorithms for image correction, because I thought using the center of the eye or the pupil position wasn't correct (which I now know to be true). But then it evolved into a need to know more about the subject because I don't like it when I can't answer a simple question. :)

I guess for FOV calculation the reduced eye models would be enough, but I need to read more papers to know why the position of their nodal point differs. If the models were all representative of a human eye the values should be identical or at least quite close.