Questions tagged [eyes]

The discussion of the anatomy and evolution of eyes. Consider using the "vision" tag for questions regarding how the brain interprets information from the eyes.

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39 views

Why does our visible range not include infrared or UV radiation? [duplicate]

As the radiation peak of the sun is in the UV region and since at around room temperature materials emit radiation at IR, I wonder why our eyes are not capable of using these wavelengths. I guess ...
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15 views

Why does Cyan appear bluish rather than greenish, when the phototopic eye sensitivity is highest in green (and Cyan contains blue and green equally)?

Cyan contains blue and green equally. Phototopic eye sensitivity is highest in green. Why, then, does Cyan appear bluish to most of us, rather than greenish?
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Can the eye determine which type of defocus is presented to it?

I have a question regarding myopic and hyperopic defocus. My question is, is the eye able to determine which type of defocus is presented to it and if so what mechanisms allow it to distinguish ...
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Functions of the layers that make up Bruch's Membrane

I have a question regarding Bruch's Membrane. Within Bruch's Membrane there are the following layers: Outer Basal Lamina Outer Collagenous Zone Elastic Zone Inner Collagenous Zone Inner Basal Lamina ...
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1answer
40 views

What is the very hard sphere inside the eye of many common fish made of and how is it called?

Inside the eye of many common fish, like tuna, scad, snapper, actually probably all fish I have eaten, is a small sphere made of some very tough substance. This sphere is even hard to crush with teeth,...
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Why do the eyes of this cat have different colours when viewed from different angles?

Why do the eyes of this cat have different colours when viewed from different angles? Both of the eyes of this cat appear yellow when looking straight at the camera. However, when the cat looks at ...
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1answer
38 views

What happens to eyeball when you push your eye muscles harder?

I have myopia and I read that the rays of light intersect before the retina. When I can not see clearly I can push somehow my eye muscles and can see a bit clearly. The object gets clear but moves ...
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How does sleep prevent our eyes from drying out?

If we don't sleep for about 16 hours, our eyes start to get dry, and no amount of eye drops helps. You use eye drops and then you're dry 10 minutes later. However, after you've slept for 8 hours, your ...
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What is the smallest visual unit perceptible to the human eye, like a pixel? (esp. in visual static)

If you close your eyes, you can often see visual static, where individual pixel-like things are much more visible than with the more smooth, crisp images one gets with open eyes. This led me to wonder ...
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25 views

Does the human eye’s field of view shrink when focusing on far away objects?

It seems like the lenses of the eye is like a fisheye lens that flattens out to a normal lens when looking at far away objects. Does that also mean that the field of view gets narrowed down as well? ...
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Vitamin A Deficiency

I have a quick question regarding Vitamin A deficiency. The photoreceptor molecules in both rods and cones have the same general structure which is retinal which is bound to a protein called opsin ...
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Why do some mammals have incomplete orbits?

I've noticed that a lot of carnivorous/omnivorous mammals (most, if not all the members of carnivora and some ancestral cetaceans), as well as some herbivores (marsupials), have incomplete orbits that ...
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1answer
85 views

Is the backward positioning of photoreceptors bad design?

(Several questions have been asked about this topic but most are quite old and there has been at least one study since then that has attempted to answer this in a new way) Since photoreceptors are ...
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1answer
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Non-Salticidae with °oo° Eye Arrangements

Since childhood, I've always thought of the °oo° pattern of four frontmost eyes as iconic for spiders (note: the pattern does not account for any additional eyes or lack thereof further to the sides ...
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1answer
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Does my nearsightedness come into play when creating light outlines in the distance?

After looking at a light and closing your eyes, you see an outline of the light. I was curious how my nearsightedness would come into play. I look at a light in the distance without my glasses on and ...
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468 views

How far can a human see at night?

I am not talking about seeing in total darkness, which I understand is not possible. I am looking more about a question how far can a human see during starry night or with half moon/full moon. I tried ...
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What standard procedure taken to measure eye far point and near point?

I've read from various link that to measure power/dioptre of eye glasses lens, we need to put far point into equation for nearsightedness and near point for farsightedness. The problem is I cant ...
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1answer
53 views

Comparion between machine vision & human vision

I hope this is the correct Stackexchange to ask this question. I am trying to know : What is the current status of knowledge regarding human vision and pattern recognition. More specifically, How ...
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128 views

(How) do horizontal pupils dialate?

I was looking at mongoose eyes in particular, but my understanding is: Circular (human-like) pupils simply get larger/smaller depending on light levels, no change in "shape" Vertical slit (cat-like) ...
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1answer
61 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 ...
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1answer
195 views

Can Green color give Rest to Eyes?

Is it correct that Green color gives rest to our eyes compare to other colors?
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1answer
84 views

What is violet color?

We have 3 color receptors in our eye, so assuming the above picture is precise we are checking for 3 wavelengths: 450nm, 540nm and 700nm. Pink for example has an RGB value of R (700nm): 1 G (540nm): ...
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If one of eyes is blind, can that eye still feel pain?

I was wondering this when I touched my bare eye (my eye was open) and since I'm not blind I was wondering if an eye is blind, can it still feel pain?
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What happens to eyelids when we feel sleepy?

Why is that whenever we feel sleepy, our eyelids start to feel heavier. It is not like we can any time close our eyes and will immediately fall asleep. But, when we feel sleepy our eyelids ...
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How many frames per second do human eyes see? [duplicate]

I observed when a helicopter rotor or fan is spinning the blades blur making it impossible to count the blades, but after a certain speed the blades seem to become visible making it possible to count ...
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What is the average eye sight for humans? How bad is one's eyesight if you are1 or 2 SD below average?

What is the average eye sight for humans? How bad is one's eyesight if you are 1, 2 or 3 SD below average? I googled but it was hard to find good search terms.
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Does cataract condition cause red film when sun is shining?

Since two years ago I have a red film in my field of vision when the sunlight (or a white spot) is at the border (or even lightly behind) of the vision field, the red color is especially obvious at ...
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Do animals with their eyes ~180 degrees apart have depth perception?

Lots of animals have their eyes more on the side of their head, like an octopus or a parrot. Are animals with eyes more on the side able to tell the depth of objects at different distances? It seems ...
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447 views

What might alien have large eyes? [closed]

Don't rush to conclusions. This is a serious question. The most widespread depiction of intelligent, "human-like" aliens are that of a species with considerably larger eyes in proportion to body ...
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Difference in frame rates of normal and peripheral vision

I recently encountered an incident in my laboratory. It was evening and the sunlight entered the lab through a window with exhaust fans. So the ray kept flickering at fixed intervals. I noticed that ...
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38 views

Why green light is good for our health? [closed]

I have a knowledge that when you woke up and see green light it increases your sight power. How it does so?
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31 views

Would preserving your Eyes from Light keep them healhty?

I read about why eyesight diminishes with age. I am aware of the fact that there are different causes that can affect the quality of image received by our eyes and that being vague would not lead to a ...
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1answer
38 views

how much can changing light enter the eye shap what you see? [closed]

Does it change the shape and how objects are seen or does it just stop you from seeing certain things?
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Does the ratio between M and L cone cells vary in one indiviual?

Wikipedia says: The ratio of M and L cones varies greatly among different people with regular vision (e.g. values of 75.8% L with 20.0% M versus 50.6% L with 44.2% M in two male subjects). This ...
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1answer
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Why did we evolve to be able to see this specific set of wavelengths only? [duplicate]

It is understandable that life didn't evolve the capability to sense all wavelengths of light, it simply didn't need it. My question is, why did it evolve the set of wavelengths it has, for example, ...
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1answer
78 views

Does night mode on iPhone really help?

Okay so I know that night mode is supposed to filter out blue light that is bad for the eyes, but is it really more helpful than annoying? At night I do use it when I’m on the phone but it doesn’t ...
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1answer
108 views

How do our eyes see an inverted image? [duplicate]

How exactly do our eyes see an inverted image of what we are looking at? Does it have something to do with the shape of our lens (i.e. convex)?
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1answer
53 views

What are reciprocal inhibitory synapses?

Quoting Kandel's Principles of Neural Science, 2013, Amacrine cells generally receive excitatory signals from bipolar cells at glutamatergic synapses. Some amacrine cells feed back directly to the ...
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1answer
548 views

What are these tiny, almost transparent, dots in my vision? [duplicate]

Sometimes when I stare at a very bright thing such as the sky I see little dots. It's actually more of a circle with a little dot inside it. They are half-transparent and they move around a lot. When ...
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1answer
2k views

What is the direction of the processing of light by the (human) retina and how does it happen?

Quoting Textbook of Medical Physiology by Guyton and Hall, 2016, page 647, ...the functional components of the retina, which are arranged in layers from the outside to the inside as follows: (...
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1answer
177 views

How many ommatidia does a honeybee have?

European honeybees (Apis mellifera) have compound eyes made of tiny facets called ommatidia. The number of ommatidia is usually known in most model insects, but I cannot find reference for the ...
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7k views

Why do eyes change colour after death?

Why exactly do eyes turn black when we die? (Or even change colour at all). The source of inspiration to this question is due to this video https://www.youtube.com/watch?v=6mNs_TcUyHc&t=627s (it's ...
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1answer
158 views

At what minimum distance the direction at which eyes point becomes parallel?

This is very similar, but different than this question about focus, let me explain why it's not a duplicate at all.. That other question is about the distance of EACH individual eye FOCUS, this one is ...
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1answer
833 views

What shape is the pupil of squirrels?

In the animal kingdom there is a striking variety of pupil shapes, with great variety among relatively close relatives. Cats have vertical slits. Siberian tigers have round pupils. Cuttlefish have a W ...
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1answer
337 views

What photoreceptors are necessary to permit infrared vision?

Humans have red green and blue photoreceptors allowing them to sense colours in the spectrum of about 400-700nm. Certain proteins allow for the extending of wavelength range in the RGB receptors, this ...
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1answer
71 views

Why do left and right eyes can require different power of lenses?

Both the eyes almost see the same things throughout our life. It is not like we use one eye more than other that it should become weaker. What causes requirement for different power of lenses for both ...
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1answer
68 views

Family eye genetics [duplicate]

Both my parents have brown eyes. My older and younger siblings have brown eyes. I have green eyes. Is this genetically possible? Back in 1962, this was questionable and led to family problems, ...
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1answer
138 views

Is it the theory of the 5 senses obsolete? [closed]

An enigmatic topic in traditional science was labelled as the mystery of the 5 senses, and how to best group senses by type. Is that theory now meaningless? Do Scientists still agree that that ...
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106 views

How do photoreceptors overcome the ambiguity of wavelength vs intensity to determine brightness? [duplicate]

I asked a similar question about the Principle of Univariance yesterday, but now I have another one. According to the Principle of Univariance, the input to a photoreceptor differs along two ...
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258 views

What is the neural coding of rod and cone cells?

In Rushton's paper on the Principle of Univariance, he states: Thus, though the rod input has two variables, wave-length and energy, the output differs only in one respect, namely 'brightness'. ...

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