Questions tagged [human-eye]

Questions about the biological function and structure of the human eye.

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34
votes
1answer
20k views

What do you see when your eyes are closed?

If you are in pitch black and you close your eyes, you sometimes can see strange shapes of various colors. A lot of the time these shapes and colors change as you observe them. This phenomenon still ...
22
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1answer
1k views

Why can't I read everything in my field of view?

When I look at a piece of text, I can see all the text on the paper, no matter where I look, because my field of view covers it all. However, if I stare at a specific word, I cannot read the text a ...
22
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3answers
30k views

Why do I see different hues of colors between each of my eyes?

Frequently, I see colors with a slightly different hue when looking through my eyes individually. The right eye is more red-tinted ('warmer' hued) and the left is typically more blue-tinted ('cooler' ...
20
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2answers
9k views

Why does getting soap in your eyes cause redness and irritation?

I am wondering why do eyes become red after getting soap in them. What is the cause behind it?
19
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1answer
45k views

What's the smallest size a human eye can see?

During a biology experiment at school, where we would look at waterweeds under a microscope, my teacher said something about that it's impossible for the human eye to see the cells without a ...
17
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3answers
3k views

Superhuman eyesight

My ten year old son was reading car number plates that were too fast, too far away and at the wrong angle for any of us to read or even believe that it was possible for him to read. We thought he was ...
16
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6answers
19k views

Why is human vision restricted to 400-700 nm?

Across the electromagnetic spectrum, 400-700 nm is a narrow spectrum of frequencies and focused in the region of short wavelengths. For example, radio waves cover a large range of frequencies ...
15
votes
1answer
545 views

Effect of pupil responses on the electroretinogram

The electroretinogram (ERG) is a measure of electrical activity of the retina. It is typically recorded from the cornea with a wire electrode or gold-foil electrode. Generally, the the ERG is ...
14
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1answer
2k views

Telling distance with one eye

Basic mathematical/logical reasoning makes it clear that you need two eyes to have depth of vision. By seeing an object from two perspectives, our brain can calculate the distance of the object based ...
14
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3answers
1k views

How do we know the brain flips images projected on the retina back around?

Why do we turn images upside down again rather than dealing with them directly, still vertically rotated after passing through our lens? I don't see how that would cause any problems, and how we'd ...
13
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1answer
10k views

Why do human eyes glow red on a photo and dog's eyes green?

Previous Research I know that cameras sometimes come with an anti "red eye" functionality that involves two flashes, presumably the second flash coincides with the shutter opening. Question Why do ...
13
votes
4answers
28k views

Why can't the human eye focus blue light?

I recently noticed that it is hard to focus on blue light sources, especially at night. When observing a blue light source, e.g. a neon sign, it looks somewhat blurry. A sign with a different colour ...
11
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1answer
3k views

Do colour blind people see white?

I know that white colour is perceived on excitation of red, blue and green cones simultaneously. It is also said that a colour blind person doesn't see a particular colour and just perceives it as a ...
11
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3answers
8k views

Why does closing one eye in bright light allow me to open the other?

I often find it physically painful to open my eyes past a squint after stepping out into the full summer sun. However, if I close one eye entirely, I can keep the other open without pain. This seems ...
10
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6answers
3k views

What is the use of eye banks, if eyeball transplants do not exist at present?

Corneas are donated and transplanted, but not the eyeball. I don't understand. What is the purpose of donating a cornea without an eyeball to a blind person?
10
votes
1answer
28k views

What is the field of view for the human eyes?

I'd like to know how much a person can see regarding the angles. If it is a rectangle, I'd like to know it's height and width. But if is another shape, I'd like to know which kind of shape and the ...
10
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2answers
3k views

Why can't our eyes smoothly transition from side to side without focusing on a moving object?

Why are we not able to slowly and smoothly look from side to side, or up and down in a single and smooth transition, given that we are able to do this if our eyes are focused on a moving object?
9
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2answers
1k views

How many mega pixels does the eye have?

What is the number of mega pixels available in the human eye? It seems that newer camera models continuously keep increasing their pixel count. However, they never seem to be capable of reproducing ...
9
votes
1answer
682 views

How does myopia develop, exactly?

Recently I was reading about myopia and I understood a few basic facts about it: Its initial cause is a constant spasm in the ciliary muscle. To do less work, the eyeball elongates a tiny bit. During ...
9
votes
2answers
96k views

What is it called when one human eye is seeing brighter color than the other?

What is the name of a phenomenon where one of the human eyes is seeing brighter/more saturated color than the other? I can observe the same object from the same position while alternating which eye is ...
9
votes
1answer
2k views

Can “red” cone cells actually see much red light?

In electronics, the most common color scheme is the "red-green-blue" (RGB) scheme. This choice is often justified by claiming that the long- (L), medium- (M), and short- (S) type cones in the human ...
9
votes
1answer
2k views

Why do we blink instead of winking each eye independently?

Question Why do we blink both eyes at the same time rather than winking each eye as needed? Why would winking independently be better? The benefit would be a minor improvement whereby a person ...
8
votes
1answer
182 views

What processes are responsible for focusing on an image only seen by one of the eyes?

When a person is spying from around a corner with only one eye, it's rather easy to ignore the other eye's image, since it's probably much darker, because one usually spies around a corner standing ...
8
votes
1answer
625 views

Is it dangerous to rub closed eyes?

Phosphene from rubbing the closed eyes where first described at least since Ancient Greece, but I caught myself thinking that I wouldn't want to try it out. So I wonder, how safe it is to actually rub ...
8
votes
1answer
100 views

Do humans squint more readily at green light?

I know that humans won't squint their eyes even if exposed to dangerous levels of ultraviolet or infrared light because our eyes simply don't have the capability to detect it. Neither do the irises ...
7
votes
1answer
23k views

How the conjunctivitis virus spread just by seeing a person's eye who is infected

Conjunctivitis or 'pink eye'. I have a few questions on conjunctivitis. When I was suffering from conjunctivitis, my doctor advised me to wear sunglasses so that no one else gets infected. I wonder ...
7
votes
2answers
342 views

Cerebral activity during exposure to non - visible light

Our eyes only have the ability to sense light within a certain spectrum. My understanding is that particular frequencies energize specific cells in our eyes, each responsible for a different "color". ...
7
votes
2answers
342 views

Why can't we half-close our eyes?

Can we half-close our eyes such that they don't vibrate? If not, then why we are unable to half-close our eyes properly? Alternatively, why isn't it possible to keep the upper eyelid close to the ...
7
votes
2answers
4k views

How does the eye know whether to focus further out or nearer in order to bring a blurry object into focus?

If the eye sees an object, but the object is out of focus, the eye could be focusing too near or too far. How does the eye (or the brain) distinguish one situation from the other? How does it know ...
7
votes
1answer
4k views

What is the rest state for eyelids - Open or Closed?

If one were to not apply any efforts on the eyelid muscles, will they remain open or closed? In movies when we see a person die, either case could happen - their eyelids could be open or closed when ...
7
votes
1answer
435 views

Why are we able to differentiate between colored objects without the presence of light?

Rods help us to see during the dark. We can see colour of the object when it reflects light. But in a dark room(room of any color but the light is switched off and it is night),we still can ...
7
votes
1answer
837 views

Does a mydriatic drug neutralize the action of a miotic?

If a person were administered a mydriatic, would the subsequent application of a miotic neutralize the action of the former? If the sequence were reversed would a mydriatic neutralize the effect of a ...
7
votes
1answer
4k views

Why do we get 'bags under our eyes'?

Why do these circles form around the eyes if somebody is tired? And why does fatigue express itself around the eyes this way? Can I get eye bags very quickly in another way? http://www.todayifoundout....
7
votes
3answers
9k views

Why can't we feel pain when the eye lid touches the eye ball?

When I press a finger on a closed eye lid it means the eye lid touches eye ball, then I didn't feel any pain. Now I open my eye lid, then I small touch(not press) the eye ball, it gives me pain, why ...
7
votes
1answer
598 views

Can one eye affect the other eye's low-light adaption?

This previous question addresses how long eyes need to adapt to darkness and reach full contrast. My question is how does one eye affect the "transition" and/or efficacy of this "night vision" of the ...
6
votes
2answers
1k views

Do eye's muscle share the same nerve?

When I try to rotate my eye, both of my eyes will rotate the same amount and in the same direction (obviously). I'm wondering if it is possible to control each eye separately. I've never seen anyone ...
6
votes
2answers
2k views

Why don't myopic people see the world upside-down?

I found this image while reading optical instruments in physics. If we look at the uncorrected rays, we see that the image they outline gets inverted. So why don't people with myopic vision see images ...
6
votes
2answers
2k views

How are colors outside the standard RGB color scheme perceived?

I found this image in a German book about biology. It's called DIN 5033 and represents the RGB color scheme. What colors are outside the RGB scheme, i.e., in the black areas of the picture?
6
votes
1answer
2k views

Would the human body react faster to touch or sight

I am currently working on an assignment for my physics class, but I believe my question is biology related. For a two person lab, I am trying to time how long it takes a tennis ball to fall two ...
6
votes
2answers
17k views

Is it biologically possible for an adult's eye color to change?

Can it be that the adult eye can change color? Specifically my question is about a unilateral color change, such that the color of one eye remains constant, while the other changes color over time. ...
6
votes
1answer
122 views

What color does the other cone in Tetrachromacy correspond to?

Human with normal vision possesses 3 cones, which correspond to blue (S), green (M) and red (L). What about tetrachromacy, where people have 4 cones in their retinae? What is the fourth cone exactly, ...
6
votes
1answer
331 views

Are all cone cells connected directly to the brain?

Coming from a computing science background, I noticed that cameras have orders of magnitude fewer wires than pixels. For example, the Raspberry Pi Camera v2 has 8 megapixels, but only 10 wires ...
5
votes
1answer
11k views

Why are irises unique?

I heard that irises are different and unique for every person. According this link, probability of two irises having identical pattern is 1 in 10 to the 78th power. That's how iris scanners identify ...
5
votes
1answer
303 views

Why eyes don't get heated while converging sunlight into retina?

It is a common observation that a magnifying glass when used to converge rays of sun to a fine point in paper, the paper burns due to intense heat. Why doesn't this happen in our eyes? Our eyes are ...
5
votes
3answers
675 views

Why do human ears have a lower boundary for the lowest energy perceivable signal than eyes?

I am currently hearing a lecture about human machine interaction. The lecturer is not a biologist (neither am I, we are both computer scientists), but he makes some statements about biology which I ...
5
votes
1answer
94 views

Do Colorblind People Have Stronger Sensitivity in Their Other Remaining Cones?

I came across this paper Color defect and color theory. The paper explained about how unilateral color blind (people who color blind only in 1 eye) actually see less bright in their color-blind eye (...
5
votes
2answers
166 views

Improving myopia

I have a friend who no longer needs glasses. He previously had myopia in both eyes but over the years it has improved until he no longer needs glasses clinically. He's had glasses for over 30 years ...
5
votes
0answers
171 views

Could being exposed to excess UV in the arctic lead to a human eye color change? If so, what is the mechanism?

The CBS News article Expedition Antarctica: A father and son's journey to save the planet says (in part): Thirty-two years ago, Robert Swan made history as the first person to walk to both poles. ...
5
votes
1answer
144 views

Where in the world does blue eyed whites originate from?

I know that there were no blue eyed people until ~6000 years ago due to a mutation and all blue eyed people have a single common anchestor. But where in the world does it originate? I assume it ...
4
votes
1answer
47 views

How do cone cells underneath capillaries receive light?

Came across this image of retina's cross section: 1) How do the cone cells directly underneath the blood vessel ('demarcated in the picture') receive a spectrally correct representation of the ...