Green Spots In Eyes

Why Do We Have Blind Spots

We're going to do a little experiment. Make sure you watch this part of the tutorialin full screen. Close or cover your left eye, look at theplus sign. Be aware of the circle, but don't focus on it! Keep looking at the plus. You may need to move your head back and fortha little bit, or move your thing closer to your face. But at some point, the circle isgoing to disappear. Now close your right eye and look at the circle.Move your head back and forth until the plus sign disappears.

You've just found your naturally occurringblind spot in each eye. And of course daily practice we do not notice this. The human eye has what you might call a fundamentalflaw. Lightsensing cells in your retina send signals to your brain via nerves. And thosenerves are in front of the lightsensing cells. Eventually, those nerves have to pass throughthe back of your eye to get to your brain and in the part of your retina where theypass through, there aren't any lightsensing cells. That's your blind spot. Now this isn't normally a problem, becausethe blind spots are located at slightly different

points in each eye, and each of your eyeswork together to fill in a complete picture. But even with one eye closed, you're notseeing a big black hole. Instead, your brain fills in what it figures ought to be there.That's why, when the circle disappears, you see the color of the background. Yourbrain is guessing, and it's guessing wrong. Although! At least one very small study foundthat you might be able to shrink your blind spot with practice. Researchers showed ten participants an imagethat fell within the margins of their blind spots and asked them to describe it. By theend of the experiment, people got a little

better at describing those images. The researchers think it's because the lightsensingcells right around the edges of the blind spots became more sensitivebetter at pickingup and passing on light signals. That's the kind of skill that's probablynot going to ever make any kind of difference in a lifeordeath situation, and humans havehad blind spots in their eyes for as long as we've had eyes. But it's a neat wayto try and hone your brain, if you're into that sort of thing. There is a different kind of creature, though,that just completely avoids this problem.

Cephalopods, like octopuses and squids, havetheir nerves behind their lightsensing cells, so there's no need for them to have a blindspot. Why did we not do it that wayé Evolution.Well I, for one, welcome our tentacled overlords. Thank you for asking, and thank you especiallyto all of our patrons on Patreon who keep these answers coming. If you'd like to submitquestions to be answered, or get these Quick Questions a few days before everyone else,you can go to patreon scishow. And if you just want to keep getting smarter withus, you can go to scishow and subscribe! Just do it.

What are those floaty things in your eye Michael Mauser

Have you ever noticed something swimmingin your field of visioné It may look like a tiny wormor a transparent blob, and whenever you try to geta closer look, it disappears, only to reappearas soon as you shift your glance. But don't go rinsing out your eyes! What you are seeing is a common phenomenon known as a floater. The scientific name for these objectsis Muscae volitantes,

Latin for quot;flying flies,quot; and true to their name,they can be somewhat annoying. But they're not actually bugsor any kind of external objects at all. Rather, they exist inside your eyeball. Floaters may seem to be alive,since they move and change shape, but they are not alive. Floaters are tiny objectsthat cast shadows on the retina, the lightsensitive tissueat the back of your eye.

They might be bits of tissue, red blood cells, or clumps of protein. And because they're suspendedwithin the vitreous humor, the gellike liquidthat fills the inside of your eye, floaters drift alongwith your eye movements, and seem to bounce a littlewhen your eye stops. Floaters may be onlybarely distinguishable most of the time.

They become more visiblethe closer they are to the retina, just as holding your hand closerto a table with an overhead light will result in a moresharply defined shadow. And floaters are particularly noticeable when you are lookingat a uniform bright surface, like a blank computer screen, snow, or a clear sky,

where the consistency of the backgroundmakes them easier to distinguish. The brighter the light is,the more your pupil contracts. This has an effect similarto replacing a large diffuse light fixture with a single overhead light bulb, which also makesthe shadow appear clearer. There is another visual phenomenonthat looks similar to floaters but is in fact unrelated. If you've seen tiny dots of lightdarting about

when looking at a bright blue sky, you've experienced what is knownas the blue field entoptic phenomenon. In some ways,this is the opposite of seeing floaters. Here, you are not seeing shadows but little moving windowsletting light through to your retina. The windows are actually causedby white blood cells moving through the capillariesalong your retina's surface. These leukocytes can be so largethat they nearly fill a capillary

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