The iris of the eye controls the amount of light. Right or wrong?

[infint]

I believe that these statements are true -
"When the pupil dilates, more light enters the eye."
"When the pupil constricts, less light enters the eye."
"In bright light conditions, the pupil constricts a little."
"In dim light conditions, the pupil dilates a little."

and that this statement is demonstrably and logically false
"The iris/pupil controls/regulates the amount of light entering the eye."

When I search the internet, I find variations of that last statement everywhere and various doctors and opticians also seem to agree and yet, I can prove to my own satisfaction that it is false. It does depend on what you mean by the words "control" and "regulate".

Before I describe the experiments that "prove" my case, I would like to know if anyone else already agrees with me.

[DrKrettin]

OK I'll buy it. I don't agree with you. I await your redefinition of English verbs with a certain degree of expectation that this is going nowhere.

[StringJunky]

 

 

I believe that these statements are true -

"When the pupil dilates, more light enters the eye."

"When the pupil constricts, less light enters the eye."

"In bright light conditions, the pupil constricts a little."

"In dim light conditions, the pupil dilates a little."

 

and that this statement is demonstrably and logically false

"The iris/pupil controls/regulates the amount of light entering the eye."

 

When I search the internet, I find variations of that last statement everywhere and various doctors and opticians also seem to agree and yet, I can prove to my own satisfaction that it is false. It does depend on what you mean by the words "control" and "regulate".

 

Before I describe the experiments that "prove" my case, I would like to know if anyone else already agrees with me.

The brain does the controlling/regulating and uses those devices to apply it.

Edited March 28, 2017 by StringJunky

[John Cuthber]

 

The brain does the controlling/regulating and uses those devices to apply it.

Interesting point. I think that reflex actions normally only get as far as the spinal column before being re-routed back. But I don't see how that could happen with the eye.

The point may be moot, some (admittedly unorthodox) viewpoints hold that the eye is part of the brain.

[StringJunky]

Interesting point. I think that reflex actions normally only get as far as the spinal column before being re-routed back. But I don't see how that could happen with the eye.

The point may be moot, some (admittedly unorthodox) viewpoints hold that the eye is part of the brain.

And you have an interesting point too, about some types of signal sources only going to the spinal column. Personally, wrt to the OP, I think it is generally assumed by everyone, and the author knows this, that the brain handles the signals and it is just convention to say that a particular organ 'controls' an input signal.

[John Cuthber]

It is a matter of semantics: does the tap control the flow of water, or is it the person who opens and closes the tap who controls it.

Neither the person nor the tap controls the flow without the action of the other.

[StringJunky]

It is a matter of semantics: does the tap control the flow of water, or is it the person who opens and closes the tap who controls it.

Neither the person nor the tap controls the flow without the action of the other.

Exactly.

[Phi for All]

!

Moderator Note

Moved from Science News to Anatomy.

[Strange]

I believe that these statements are true -

"When the pupil dilates, more light enters the eye."

"When the pupil constricts, less light enters the eye."

"In bright light conditions, the pupil constricts a little."

"In dim light conditions, the pupil dilates a little."

 

and that this statement is demonstrably and logically false

"The iris/pupil controls/regulates the amount of light entering the eye."

 

 

If one or more of the initial statements are true, then the final one must also be. It is just a more general statement of all of them.

 

But feel free to present your "logic" and the data that "demonstrates" it is false.

[Raider5678]

 

 

If one or more of the initial statements are true, then the final one must also be. It is just a more general statement of all of them.

 

But feel free to present your "logic" and the data that "demonstrates" it is false.

Brain controls the size of the iris. The iris controls the amount of light that gets in.

But it can also widen for other reasons.

Such as seeing an attractive women, or being in a state where you're ready to reproduce.

Fear also dilates the eyes.

 

Although I still have no idea where he's going with this. So I still agree with you. Just pointing those out.

Edited March 28, 2017 by Raider5678

[infint]

Apologies. In considering my reply, I belatedly realised that I made a mistake. Not counting artificial mechanisms like sunglasses, the pupil is the only available means by which the eye can adjust the amount of light striking the retina. As worded, the statement is correct. The problem is that everybody seems to accept that the pupil is the main means by which the eye adapts to different light levels and that's the idea I want to challenge. Perhaps I am now "preaching to the converted" but I will present my evidence anyway.

 

Experiment 1. I stand in front of a mirror in a darkened room and use a small torch to adjust light levels. My pupils barely react. At most, the change in diameter is about 2:1. I can just about read a book in bright moonlight and I can read the label written on the glass of a working 40W light bulb. There is no way that the pupil could adjust for that variation in light level.

 

Experiment 2. I use my smartphone camera to take a picture of a working wall light and it doesn't look anything like what I can see with my eyes. Either the surroundings are too dark or the light is too bright. I say that this is because the camera can only adjust the whole image while my eyes can adjust on a cell by cell basis and it's the individual cells of the retina that do almost all of the adjustment for different light levels.

 

I also understand that the pupil dilates or constricts in response to pain, drugs, disease, interest and imagination.

[Klaynos]

Your visual system is a complex signal processing system with a dynamic nonlinear sensor on the front of it.

 

Your experiments do not try and control for any of this. What you've done is shown than the amount of light hitting the sensor isn't the only factor involved.

[John Cuthber]

Apologies. In considering my reply, I belatedly realised that I made a mistake. Not counting artificial mechanisms like sunglasses, the pupil is the only available means by which the eye can adjust the amount of light striking the retina. As worded, the statement is correct. The problem is that everybody seems to accept that the pupil is the main means by which the eye adapts to different light levels and that's the idea I want to challenge. Perhaps I am now "preaching to the converted" but I will present my evidence anyway.

 

Experiment 1. I stand in front of a mirror in a darkened room and use a small torch to adjust light levels. My pupils barely react. At most, the change in diameter is about 2:1. I can just about read a book in bright moonlight and I can read the label written on the glass of a working 40W light bulb. There is no way that the pupil could adjust for that variation in light level.

 

Experiment 2. I use my smartphone camera to take a picture of a working wall light and it doesn't look anything like what I can see with my eyes. Either the surroundings are too dark or the light is too bright. I say that this is because the camera can only adjust the whole image while my eyes can adjust on a cell by cell basis and it's the individual cells of the retina that do almost all of the adjustment for different light levels.

 

I also understand that the pupil dilates or constricts in response to pain, drugs, disease, interest and imagination.

It seems that you have failed to account for the eye having a very large dynamic range,

Even without help from the pupil, it can cover a large range of lighting conditions.

The pupil then (generally) helps a bit more.

Expt 2 shows how clever your brain is.

[Strange]

Apologies. In considering my reply, I belatedly realised that I made a mistake. Not counting artificial mechanisms like sunglasses, the pupil is the only available means by which the eye can adjust the amount of light striking the retina. As worded, the statement is correct. The problem is that everybody seems to accept that the pupil is the main means by which the eye adapts to different light levels and that's the idea I want to challenge. Perhaps I am now "preaching to the converted" but I will present my evidence anyway.

 

Experiment 1. I stand in front of a mirror in a darkened room and use a small torch to adjust light levels. My pupils barely react. At most, the change in diameter is about 2:1. I can just about read a book in bright moonlight and I can read the label written on the glass of a working 40W light bulb. There is no way that the pupil could adjust for that variation in light level.

 

Experiment 2. I use my smartphone camera to take a picture of a working wall light and it doesn't look anything like what I can see with my eyes. Either the surroundings are too dark or the light is too bright. I say that this is because the camera can only adjust the whole image while my eyes can adjust on a cell by cell basis and it's the individual cells of the retina that do almost all of the adjustment for different light levels.

 

I also understand that the pupil dilates or constricts in response to pain, drugs, disease, interest and imagination.

 

 

Most of what you see is constructed by the brain. This includes levels of brightness. For example, the squares A nd B in this image are the same colour but your brain tells you otherwise

https://en.wikipedia.org/wiki/Checker_shadow_illusion