pupil and iris diameter the same in all people?

[pluto2]

Is the diameter of the pupil and iris the same in all people or are there variations between people?

The iris is the contractile membrane perforated by the pupil and forms the colored portion of the eye.

 

[Ophiolite]

Are the answers to this question likely to differ between the two threads you have opened on the subject?

 

[pluto2]

Are the answers to this question likely to differ between the two threads you have opened on the subject?

Sorry I accidently posted two of them.

 

[CheskiChips]

This is not a matter of Genetics, rather psychophysiology, unless you're making a brash statement about pre-determination. I know melanin variation does effect the total absorption of light, different eye colors are a result of melanin variation. Thus blue eyes would be most likely dilated different than brown eyes in certain circumstances.


http://portal.acm.org/citation.cfm?id=861059#CIT

http://books.google.com/books?id=FY...X&oi=book_result&resnum=3&ct=result#PPA224,M1

 

[Hercules Rockefeller]

Is the diameter of the pupil and iris the same in all people or are there variations between people?

The iris is the contractile membrane perforated by the pupil and forms the colored portion of the eye.

Hi pluto2,

We have a poster on SF by name of madanthonywayne. He is an optometrist and, not surprisingly, is good at answering eye-related questions. He doesn’t post much in B&G but I’ll see if I can get him to come over and give your question a shot. Stay tuned....

 

[madanthonywayne]

Is the diameter of the pupil and iris the same in all people or are there variations between people?

The iris is the contractile membrane perforated by the pupil and forms the colored portion of the eye.

Both the pupil and iris diameter vary between individuals.

The size of the iris is primarily a function of the overall size of the eye. In general, people who are far-sighted have smaller eyes and smaller irises. People who require no optical correction (emetropes) have average sized eyes. And people who are near sighted have large eyes. There are certain pathological conditions that can result in variations in the size of the eye such as congenital glaucoma. The increased pressure literally stretches out the highly elastic eye of the infant resulting in giant eyes as shown below:

And here's a picture of a child with congenital glaucoma in just one eye:

Now pupils, on the other hand, vary in size constantly according to light conditions. Constricting in bright light and dilating in dim light. Nevertheless, the amount of dilation/constriction varies between individuals so much that one person's pupils in a bright room might be smaller than another's in a dark one.

The primary determinent at any given time is the relative stimulation of the pupil dilator muscle and the pupil constrictor muscle. When we are excited, or scared, or aroused; our pupils dilate to allow the maximum amount of light in and increase our peripheral vision. It is thus part of our fight or flight response and stimulated by the simpathetic nervous system. On the other hand, when we're bored, tired, sleepy the parasympathetic system takes over and our pupils constrict.

Furthermore, we start out as babies with very small pupils. By the time we're teenagers, our pupils have reached their maximum size. Then, they begin shrinking and, by our seventies or eighties are usually quite small.

 

[pluto2]

Furthermore, we start out as babies with very small pupils. By the time we're teenagers, our pupils have reached their maximum size. Then, they begin shrinking and, by our seventies or eighties are usually quite small.

Thanks for the answer madanthonywayne. Are our pupils even smaller in our seventies and eighties than when we are babies?

Now pupils, on the other hand, vary in size constantly according to light conditions. Constricting in bright light and dilating in dim light. Nevertheless, the amount of dilation/constriction varies between individuals so much that one person's pupils in a bright room might be smaller than another's in a dark one.

So what is the cause of this variation between individuals? Is it the pupil muscles or is it genetic?

 

[madanthonywayne]

Thanks for the answer madanthonywayne. Are our pupils even smaller in our seventies and eighties than when we are babies?

I've not seen the exact numbers, but I'd bet it's old people with the smallest pupils. I know most really tiny pupils I come across are in the elderly.

So what is the cause of this variation between individuals? Is it the pupil muscles or is it genetic?

All other things being equal, the differences are probably genetic. But a person's pupil size at any given time is due to variety of factors including: Amount of light, emotional state, use/abuse of drugs, age, etc.

Here's an interesting fact. Women in the middle ages were perhaps aware of the age/pupil size correlation and would rub their eyes with the bella donna plant to look younger. The Bella Donna plant is the source of atropine, the basis of all dilation drugs. This practice is the reason the plant is called Bella Donna, which means beautiful woman.

 

[pluto2]

genetic. But a person's pupil size at any given time is due to variety of factors including: Amount of light, emotional state, use/abuse of drugs, age, etc.

Regarding emotional state, emotions are really complex and many times we experience several of them. So how do the pupils behave when we're happy or in a good mood, when smiling at someone friendly or funny, when sad or depressed, when busy or preoccupied with something and when thinking or pondering?

 

[Ophiolite]

Sorry I accidently posted two of them.

I just re-read my post. If it sounded rude, my apologies. That was not the intent. I was trying for humour. I'm not very good at humour.

 

[pluto2]

I just re-read my post. If it sounded rude, my apologies. That was not the intent. I was trying for humour. I'm not very good at humour.

Ah no it's alright. I wasn't offended or anything. I'm not good at understanding humour.