Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: Quantumcat on 01/12/2003 16:08:04
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When I push on my eyeball with a finger I see a little black spot that increases in size the more I push, and as I push a second image of what I'm looking at seperates from the first, and moves farther the more I push. The black spot is in the opposite side to the side I push on. If anyone can explain why it happens that would be nice. Thanks.
Also another thing, why is it that when I rub the length of a finger up and down the inside of my arm (in a certain place) I get an extremely weird feeling up my arm and in my hand. And I mean extremely weird. TIA.
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is the black spot you can see your finger ?! [:D]
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No. It's something cloudy, and as I said it's in the opposite side of my vision to where my finger is.
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Maybe the black spots are floaters. Don't know about the spot on your arm. Where exactly are you rubbing?
Bezoar
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I'm pretty sure that's your finger you're seeing....or the impression it makes on your eyeball anyway. Move it around a little when you're pressing on your eye, and you'll see the black spot move in a manner opposite to how your finger is moving. (presumably because light refraction through the cornea reverses the image you see) Dunno why you get a black imprint in the shape of your finger when you do that though....maybe because you're blocking all ambient light in the section you're touching, compared with your eyelid that is thin and doesn't block light as well. The extra photon blocking maifests as a black spot.
I dunno...not my area of expertise, just some speculation.
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You eyeballs are wired together via the brainstem so that the optical axes of each are aligned for conjugate vision. Damage to one of the 3 nerves supplying the ocular muscles results in double vision when the person tries to look in the direction that that nerve would normally move the eyeball. This occurs because one eye moves and the other doesn't so the 2 retinae see different things and they are misaligned.
You can over-ride this optical alignment by pushing on your eyeball. This will create a blur on the opposite side (you don't see the one on the same side because it is masked by your finger) as the visual images go out of register. The right side of your brain processes all of the visual image on the left - although both eyes make a contribution to the visual field on each side (complicated, but true and this is why you get the rather strange effect you are describing).
Chris
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cannabinoid, I don't try by putting my finger on the cornea (ouch!!) but on the schlera, so it doesn't block any light. And chris, I didn't completely understand your explanation of the double vision but most likely you're right :-P
Another questions, why is it if I close my eyes and rub or press slightly on my eyeballs I see all these pretty swirls of colour?
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Hi, I have a question I was hoping that someone would be able to answer.
For the past week and a half, I have been seeing a black spot on my left eye. I mean that when my eyes are open, as I am looking out of them I see this black spot (or a shadow of a black spot). Sometimes when I blink, it goes away. I was told by a friend that it could be something called a floater and that it may not be a major problem. I also heard that it could be something more serious. Does anyone know what eles it could be, and is it imperative that I go see a doctor now, or can I wait a few weeks?
Thanks
Jennifer
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Sounds like a floater. Where they can be a sign of something more serious, without any other health or visual problems, I'd tend to think it could wait for the next eye appointment. Sometimes, they resolve by themselves. However, I would get it checked.
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Thanks
Jennifer
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hi,i hope someone can help me.For the past 1-2years i have been seeing black like floaters in my right eye.Went to eye doctor,he said everything looked ok.Still concerened so went to family practice dotor,he was worried so had a MRI done on the right side of my brain and eye.Nothing....everything still coming back ok.Now within the past 9months noticed spots in my left eye,these spots never go away.So with more concern went back to doc. he said everything still ok.The spots are pregressively getting worse in both eyes noticing some twitching in both eyes.Scared...can anyone help??????
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Ok, I'm not sure if any of these are exactly what you are talking about, but here are a few related phenomena that I know about:
"Floaters", are usually described as small black squggily spots on your eye, although I suppose they could be coloresd to some people. The follow with your vision as you move your eye. You don't notice them very often, but they're in the same spot your whole life. From what I hear most people have one or two. I read once how they were formed. I don't remeber the exact details, but I know it was something like a blood vessel that broke while you were still a fetus or something like that.
The spots you get when you stare at the sun, are form over stimulation of your eyes, your eyes only have a certain intensity range to which they can sense, everything else after that registers the same. They stay after you look away for the same reson your ears ring after a rock concert; your cells need time to recover after such intense stimulation (neither is a good thing)
This is a copy/paste of a post I wrote earlier today in another thread (geeze, don't you people read around? [:p]) Any ways I believe it relates to a few of the questions brought up in this thread. Floaters aren't typically a big deal. You probably just notice them more as you worry yourself about them. Quantumcat your question is definately answered below. OK here's what i had written:
When you turn off the liughts real quickly and still see spots, thats just left over neurotransmitters in your synapses that hasn't been re-uptaken or enzymatically degraded yet.
Also if you poke yourself in the eye, or hit yourself on the back of the head you see light. This is your sensory receptors responding to a different type of stimulus than they are used to. While your eye is designed to detect light (and is best for that job) if there is a strong enough level of another stimulus (touch, for example) it can detect that stimulus, but it reports it in the way its used to reporting (ie. your eye gets touched, but your brain reads "light" because thats whgat it usually gets from your eyes)
OK, enough typey typey, I should go get to work.
Lastly quantumcat, where on your arm are you pushing? (makes a big difference regarding the answer)
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Then why are they black?
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I'm not sure, since its not a natural thing for your eye to be responding to anyway, I'm sure it works kind of wierdly. Your eyes aren't SUPPOSED to react to touch, its just that through evolution and development they are so similar to other sensory receptors that they do by accident.
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Then why are they black?
Am I dead? Am I alive? I'm both!
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I'm not sure, since its not a natural thing for your eye to be responding to anyway, I'm sure it works kind of wierdly. Your eyes aren't SUPPOSED to react to touch, its just that through evolution and development they are so similar to other sensory receptors that they do by accident.
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