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Medical Can a human eye magnify an image?

  1. Dec 4, 2007 #1

    Ivan Seeking

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    I once worked with a guy who had been hit in the head by lightning. As he described it, he was sitting on his porch and looking at a stop sign about a quarter-mile up the road. The last thing that he remembers - apparently at the moment of the strike - was the stop sign appearing to be magnified. He recalls it appearing to grow something like three or four times larger than normal. Some number of days later he awoke in the hospital.

    I assume that the working explanation is that the effect was psychological. But I have always wondered if is possible that this might have been a physical effect caused by a deformation of the eye and lens due to the strike. Considering the energy, and especially the power involved in a direct strike, very unusual effects might be expected.
     
  2. jcsd
  3. Dec 4, 2007 #2
    This is a very interesting point. I will do some research.
     
  4. Dec 5, 2007 #3

    Danger

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    Intriguing, alright.
    My first thought would be tunnel vision, such as is experienced by combat shooters, wherein all extraneous visual input is filtered out to leave the target as the sole focus of attention. Did your buddy happen to mention if the image became more clearly focused as opposed to just larger?
     
  5. Dec 5, 2007 #4

    turbo

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    It could be that when he was hit, he lost peripheral vision and was left with the imagery from the fovea, giving the impression that the stop sign more fully occupied his field of view.
     
  6. Dec 5, 2007 #5

    Ivan Seeking

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    I am sure that he was convinced that the sign actually appeared to be larger; not only because he was perplexed by this, but also because it was about the only memory that he had of the event. I remember being surprised by his statement and asking him about it, but I can't be any more specific.
     
  7. Dec 5, 2007 #6

    DaveC426913

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    I would be very critical of any memories preceding a traumatic incident like that. How can we be sure it's a memory at all?

    Assuming that for the moment,

    It seems to me that the sphere of the eye changing shape would merely make it go out-of-focus. To magnify it would require a change in the shape of the cornea's thickness i.e. thin around the edge, thick through the middle, or somesuch.

    Not only is this implausible in the extreme, but I don't see how it could magnify without losing focus.
     
    Last edited: Dec 5, 2007
  8. Dec 7, 2007 #7

    Moonbear

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    I agree with this, a distortion would leave the image blurred (but maybe it was and he just doesn't recall that part). It really makes the most sense that it was a change in the processing of the image in the brain, not something physically changed about the eye. Something as major as a lightning strike is undoubtedly messing up neural impulses. It also could have been just a hallucination, or even a dream after he was rendered unconscious.
     
  9. Dec 7, 2007 #8

    Ivan Seeking

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    What about a change in the concavity of the vitrious chamber? This could increase the area on the retina affected by an image. Also, is it possible to change the shape of the lens, say by stretching, or would this certainly result in permanent eye damage?
     
    Last edited: Dec 7, 2007
  10. Dec 7, 2007 #9

    DaveC426913

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    I still don't see how it would stay in focus.
     
  11. Dec 7, 2007 #10

    russ_watters

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    The lens is a lens - changing the magnification comes from a change in the focal length. So not only would the lens need to change shape, but the eye would need to become larger to bring it back into focus.
     
  12. Dec 7, 2007 #11

    Integral

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    1x for the human eye is defined to be the angular size of an object at 25cm. To get 2x magnification simply move the object to 12.5cm.

    Myopics make great human microscopes. Without my contacts in I need to bring an object to about 5cm from my eye to focus on it, this is equivalent to a 5x microscope. In ancient times myopics were employed to do fine etching on jewelry and such.
     
  13. Dec 8, 2007 #12

    Integral

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    A change in index of refraction of the aqueous humour would move the apparent location of the image. Seems like this could easily be seen as a change in image size by the brain. The temperature change which is bound to accompany a lighting strike could easily change this property.

    So, the way I see it such a change seems completely physical.
     
  14. Dec 8, 2007 #13

    Danger

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    It seems that there's nothing for it but to strap the guy down and zap him again under laboratory conditions. :devil:
     
  15. Dec 8, 2007 #14

    russ_watters

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    True, but in the example in the OP, we didn't get any indication that the lightning strike threw him 880 feet.
    That may be plausible unless the temperature change required to change the index of refraction by that much would also cook the person!
     
  16. Dec 8, 2007 #15
    The size of an image would increase fourfold if you could stretch the focal distance of the eye by a corresponding amount. Imagine your eye bulging a few inches out of your skull. Another way to make an image appear 4X larger is to displace all light cones of the retina so that they are this much closer to each other. If the retina could "contract" in such a manner then we would all have built-in telescopes inside our eyes. But we don't. The tunnel-vision scenario sounds most likely to me.
     
  17. Dec 8, 2007 #16

    Integral

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    I can conceive of temperature changes somewhat less then that required to cook the eye, as well as I can a lighting strike providing sufficient energy to cook the eye. The eye resides in an area of the body which is closely temperature controlled, perhaps a small change would make a difference. We must also keep in mind that there is much more to our vision and perception then the simple formation of an image.
     
  18. Oct 9, 2011 #17
    funny i stumbled upon this topic

    When i was younger i used to be able to do this to a limited degree,

    It involved going to church and being bored out of my brain. the church had a certain type of tile work on the floor almost mosaic size tiles same size as your keyboard letters but not making any sort of large picture just a few shades of brown,cream,white etc.

    anyway allot of time in church was spent standing up at the very back and just staring at the tiles after a while i noticed that if i crossed my vision and let it slowly line back up (height of boredom i know) that at a certain stage before full straightness they would settle in a new position that didn't feel cross-eyed but left the floor at about waist to chest height in my field of view and the tiles looking about twice the size. have not been able to replicate this since as it was not something i was particularly interested at that stage but may revisit that church to see if the floor is still there. maybe its the small tiles that give some sort of distortion but they defiantly looked magnified.
     
  19. Oct 9, 2011 #18

    DaveC426913

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    This thread is 4 years old.
    Your experience is not related to the experiences of the thread.
    I've spent much time (as a child) staring at the patterns in the ceiling at my church.
    I've also spent time (as an adult) looking at stereoscopic patterns.

    What you are describing is an effect of stereoscopy and geometry.

    Your brain uses many cues to tell the sizes of objects in front of you. One of those cues is the angle of your two eyes. When focusing on anything nearer than infinity, the lines of sight from and object to each your eyes will not be parallel; they form a very acute triangle with the object at the apex. The brain uses this angle (again, along with many other clues) to judge the distances to objects.

    If a pattern is similar enough (and has a high enough repetition rate), it is possible to get each of your eyes to focus on two different sections of the pattern. If your eyes are not both pointed at the same object, the angle of your eyes will be either wider or narrower (both are possible, depends on the pattern and on your eyes). Your brain picks this up and tells you the objects are farther away than they really are.

    In order for them to be farther, yet still appear the same angular size, they must be larger than expected. This is what you experience as magnification. You expect the patterns to be, say 2 inches across, but your brain says, no if they're that far away that would make them more than 4 inches across.
     
    Last edited: Oct 9, 2011
  20. Oct 10, 2011 #19
    Things suddenly seeming larger than they are is called "macropsia". It is associated with several conditions, the most common being migraine, simple partial seizures, and mononeucleosis.

    http://en.wikipedia.org/wiki/Macropsia


    (The wiki article is OK but incorrectly associates it with complex partial seizures. It is actually the result of the simple partial seizures that constitutes the "aura" of the complex partial, or which can happen in isolation. [Many, but not all, serious seizures start with a simple partial and then escalate to something involving more of the brain. The simple partial, though, can happen in isolation without ever progressing.] )

    Due to the electrical nature of the event in the OP I would think this episode of macropsia was a simple partial seizure that preceded the loss of consciousness. About the quickest way to give a perfectly healthy person a seizure is a good jolt of electricity to the brain.

    The article doesn't do a good job of distinguishing between episodic macropsia and macropsia as a lingering experience. In seizures and migraine (episodic phenomena) it is doubtful to me that the eyes have anything to do with it, rather, it's a cortical phenomenon (analagous to a digital, rather than an optical, zoom in photography). The longer lasting conditions talked about in the article could well be explained by problems in the actual eye, the retinal compression.

    On the other hand, the effects of non-lethal lightning strikes on humans is poorly understood. It could well be that the strong magnetic field caused some kind of contraction of the retina.
     
  21. Oct 10, 2011 #20
    Dave, are you able to do this? I've tried with no luck.
     
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