pupil and iris diameter the same in all people?

Discussion in 'Biology & Genetics' started by pluto2, Dec 22, 2008.

  1. pluto2 Registered Senior Member

    Messages:
    766
    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.
     
  2. Google AdSense Guest Advertisement



    to hide all adverts.
  3. Ophiolite Valued Senior Member

    Messages:
    9,232
    Are the answers to this question likely to differ between the two threads you have opened on the subject?
     
  4. Google AdSense Guest Advertisement



    to hide all adverts.
  5. pluto2 Registered Senior Member

    Messages:
    766
    Sorry I accidently posted two of them.
     
  6. Google AdSense Guest Advertisement



    to hide all adverts.
  7. CheskiChips Banned Banned

    Messages:
    3,538
  8. Hercules Rockefeller Beatings will continue until morale improves. Moderator

    Messages:
    2,720

    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....

    Please Register or Log in to view the hidden image!

     
  9. madanthonywayne Morning in America Staff Member

    Messages:
    12,461
    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:

    Please Register or Log in to view the hidden image!


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

    Please Register or Log in to view the hidden image!



    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.
     
  10. pluto2 Registered Senior Member

    Messages:
    766
    Thanks for the answer madanthonywayne. Are our pupils even smaller in our seventies and eighties than when we are babies?

    So what is the cause of this variation between individuals? Is it the pupil muscles or is it genetic?
     
    Last edited: Dec 23, 2008
  11. madanthonywayne Morning in America Staff Member

    Messages:
    12,461
    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.
    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.
     
  12. pluto2 Registered Senior Member

    Messages:
    766
    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?
     
    Last edited: Dec 24, 2008
  13. Ophiolite Valued Senior Member

    Messages:
    9,232
    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.
     
  14. pluto2 Registered Senior Member

    Messages:
    766
    Ah no it's alright. I wasn't offended or anything. I'm not good at understanding humour.
     

Share This Page