Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Medical Does closing your eyes conserve energy?

  1. Dec 30, 2011 #1
    I'm no scientician, so I was wondering if your eyes not getting any light would actually decrease the amount of energy you'd be using?
     
  2. jcsd
  3. Dec 30, 2011 #2

    Pengwuino

    User Avatar
    Gold Member

    Why exactly do you think that would happen?
     
  4. Dec 30, 2011 #3
    'Cause I don't know how eyes work and thought maybe if they "weren't doing anything" they wouldn't consume as much energy. Obviously they would still be getting some light coming through the eyelids, but less of it, at least.
     
    Last edited: Dec 30, 2011
  5. Dec 30, 2011 #4

    Evo

    User Avatar

    Staff: Mentor

    What are your concerns about "energy use"?
     
  6. Dec 30, 2011 #5
    Your brain could conceivably use more energy trying to interpret what's going on around you in the absence of sight information than you'd save in the absence of processing the sight information you were shutting out.
     
  7. Dec 30, 2011 #6

    Ryan_m_b

    User Avatar
    Staff Emeritus
    Science Advisor

    When light enters the eye it breaks down a molecule known as rhodopsin. The breakdown of this chemical activates a signalling pathway in a photoreceptor cell that culminates in a signal being sent to the brain. The photoreceptor continually reforms the rhodopsin so that you can continually see. I'm dredging this memory way up from high school but I'm pretty sure that if you close your eyes your photoreceptors will continue to synthesise rhodopsin for up to 50 minutes without light; this is why when you switch off the light at night it seems pitch black but if you wake up a few hours later everything is a lot clearer. So from that simple point of view when your photoreceptors are not being stimulated with light after 50 minutes they become minutely less metabolically active. Also the nerves that transmit the impulse would be minutely less active.

    However the energy this would save would be far less than negligible, a bit like turning off a single lightbulb in a city. And as has been pointed out there are other factors at play like whether or not the brain uses more energy in other areas to compensate for the lack of vision.
     
  8. Dec 30, 2011 #7
    Thanks.

    I was really just curious. I don't think I'm going to set up a human-powered energy farm anytime soon :tongue: . I happened to get up in the middle of the night for a midnight snack and thought it might be interesting to do so with my eyes closed. I was sufficiently amused by the experience and got to thinking about the concept of this thread.

    This occurred to me as well, but it sounded to me like something that would be too complicated for people to have figured out, yet, so I'd have to settle for this one aspect of the total answer :tongue: .
     
  9. Dec 31, 2011 #8
    beside energy consumed by the brain to interprete images ,and the neglicable energy used for rhodopsin synthesis , there is also energy consumed by the eyes' muscles used to keep both eyes focused at a single point
     
  10. Jan 7, 2012 #9

    Drakkith

    User Avatar

    Staff: Mentor

    I think this is due to aquiring your "night vision", not because your receptors are doing anything different. Houshold lights are more than enough to keep your pupils from opening to their maximum extent.
     
  11. Jan 7, 2012 #10

    Ryan_m_b

    User Avatar
    Staff Emeritus
    Science Advisor

    Pupillary reflex does contribute but it is mainly due to the reforming of rhodopsin, taken from wiki;
     
  12. Jan 7, 2012 #11

    Drakkith

    User Avatar

    Staff: Mentor

    Interesting! Everything I've ever read has just been about the size of the pupil.
     
  13. Jan 7, 2012 #12

    Ryan_m_b

    User Avatar
    Staff Emeritus
    Science Advisor

    If you want a cool and simple experiment to do at home blindfold one eye making sure that there is absolutely no light going into that eye for about an hour. After the hour is up you can either go into a room that is pitch black or (if it's easier) do this at night and turn off all the lights. Regardless once you are in a pitch black room and can't see anything take off the blindfold and compare how much you can see out of each eye. It really is amazing!
     
  14. Jan 19, 2012 #13

    Ryan_m_b

    User Avatar
    Staff Emeritus
    Science Advisor

    The brain is massively energy intensive, I have a vague recollection of being told that it consumes 20% of our energy in a lecture a long time ago (but take that with a pinch of salt). As for coma patients it seems they still need 2400 calories a day according to this article on coma patient care. That doesn't really surprise me because even living a sedentary life the body uses a lot of energy.
     
  15. Jan 19, 2012 #14

    DaveC426913

    User Avatar
    Gold Member

    No. The reason for the difference is your pupils - they take as much as 30 minutes to fully dilate.
     
  16. Jan 19, 2012 #15

    Drakkith

    User Avatar

    Staff: Mentor

    Doesn't post #10 explain why?
     
  17. Jan 19, 2012 #16

    apeiron

    User Avatar
    Gold Member

    It seems that the full story is even more complex than just manufacturing pigment. There is an adaptive shift in neural processing style as well. Gotta love the sophistication of the brain!

     
  18. Jan 19, 2012 #17

    DaveC426913

    User Avatar
    Gold Member

    Sorry. Somehow I managed to skip over a dozen posts. Retracted.
     
  19. Jan 19, 2012 #18

    DaveC426913

    User Avatar
    Gold Member

    I've done this. It's crazy. It actually feels like there's something blocking your one eye - like a black pillow covering it.

    (However, in-and-of-itself it does not confirm or refute the contention re: the pupil versus rhodopsin explanation.)
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Does closing your eyes conserve energy?
Loading...