38 votes
Accepted

What do you see when your eyes are closed?

This is called a phosphene — the experience of perceiving light in the visual cortex without light actually entering the eye. This commonly happens due to stimulation of the retinal ganglion ...
  • 3,139
33 votes
Accepted

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

Very nice question! First of all, the 'smallest size' that a human eye can perceive is called visual acuity, and can be expressed in various ways. It cannot simply be expressed by means of size ...
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30 votes

Why do blood vessels in the eye not obstruct vision?

Avoid the fovea Figure 2 from the same paper shows the distribution relative to the fovea: As you can see, it's pretty much devoid of this superficial vasculature, so anything you are directly ...
  • 37.1k
27 votes
Accepted

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

The field of view is determined by the light-receptive parts of the eye: the retinae (Kolb, 2012). The fovea is the region with the highest resolution. It is located in the central part of the retina ...
  • 51.5k
23 votes
Accepted

Why is human vision restricted to 400-700 nm?

Short answer The visible spectrum has the highest energy in sunlight at the earth's surface, explaining the gross location of the visible spectrum in life on earth. The specific frequency range varies ...
  • 51.5k
22 votes

Telling distance with one eye

Depth perception consists of what are called monocular cues and binocular cues. As you mention, binocular vision has a lot of advantages for depth perception, but it is not completely necessary. Many ...
  • 37.1k
17 votes
Accepted

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

You can't catch conjunctivitis by looking at someone, but you can spread it around by touching your eye and touching something else, which then can pass the virus to someone else (viral conjunctivitis ...
17 votes

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

You are asking two questions that you think are connected but are actually not. Question 1 - What is the use of eye banks? Answer: It's to store corneas for transplant for people with cornea ...
  • 271
17 votes
Accepted

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

Short answer In humans it is basically the red choroid plexus in the back of the eye you are seeing on a flashed photo, while it is the green-reflecting tapetum lucidum in dogs. Background The red-...
  • 51.5k
17 votes

Superhuman eyesight

Short answer Visual acuity decreases with age. Your son's age is within the age range that visual acuities are best. Acuity starts to decrease from about age 45. Background Visual acuity (visual ...
  • 51.5k
15 votes

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

I used to work at an eye bank so I have a bit of knowledge about this, though some of it may be out of date. There are several aspects to an eye bank. The corneas are one of the primary things that ...
  • 250
14 votes
Accepted

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

This is because of the soaps chemical nature. They are alkaline agents and human eyes have a very low tolerance for alkalinity. Human eyes are roughly neutral with a pH of around 7, and soaps are ...
14 votes
Accepted

Do eye's muscle share the same nerve?

Each eye is controlled separately. Three cranial nerves emerge at the brain for each eye to control the so called extraocular muscles. That we usually move both eyes in one direction is due to that ...
  • 2,068
13 votes
Accepted

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

You have misinterpreted the nature of the light rays shown in the diagram in the question. The two rays are representing light coming from the same (distant) point in the environment, that is, some ...
  • 8,759
13 votes
Accepted

What is the field of view for the human eyes?

The general shape of the field of view has been answered in the related question "If human eyes watch an area, what's the shape of its capturing shape? Rectangular? Half spherical?" Regarding the ...
  • 51.5k
13 votes

Why do blood vessels in the eye not obstruct vision?

You CAN see your blood vessels! Following-up from Bryan Krause's answer: Bryan mentioned that the blood vessels are typically not visible partially because they are unchanging (i.e., static). In ...
12 votes
Accepted

Do colour blind people see white?

No not white or grey generally, it's a mix of other colors, they often have low resolution of a particular color. Here's a page where you can mouse over a color wheel and see a version in color ...
11 votes

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

This is an interesting phenomenon which I have been aware of for several years, but I haven't yet come across any official description of it or explanation for it. Nonetheless, the phenomenon is easy ...
  • 873
10 votes

Why is human vision restricted to 400-700 nm?

Most of the light from the sun doesn't actually reach the earth's surface due to the atmosphere. [source] So the light reaching earth includes near-UV, visible, near-IR and a band of radio waves. ...
  • 17.5k
10 votes
Accepted

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

This depends to some extent on how you define "resting state" (it matters). Innervation of the eye occurs in the brainstem and upper spinal column, so is, like most brainstem functions, on autopilot ...
9 votes
Accepted

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

No-one can re-implant an entire eye, because the optic nerve has been severed in one who has lost an eye. A cornea can't be grafted to a glass eye. But blindness isn't only caused by loss of the ...
9 votes
Accepted

How does myopia develop, exactly?

What is myopia? Myopia, a.k.a. near-sightedness, is a refractory error. Refraction is the process by which the optical system focuses images of objects on the retina, which are then transmitted to ...
  • 3,139
9 votes

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

Short answer: The genes that encode eye color do not change, but the pigments in the eye can change due to external factors like diseases of medication. Long answer: Yes, it is possible that the eye ...
  • 49.4k
9 votes
Accepted

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

Short answer Smooth pursuit is driven by retinal slip, which is determined by external input registered peripherally in the retina. Background The smooth pursuit system is a system designed to ...
  • 51.5k
9 votes
Accepted

Can "red" cone cells actually see much red light?

This is a good question. The first thing to note is that human colour vision is very complex and still poorly understood. If you visit the wikipedia page on RGB, you will find that this correctly ...
  • 807
9 votes

If one of eyes is blind, can that eye still feel pain?

Blindness can be due to a damage of the lens, retina, optic nerve or the visual area at the occipital lobe of the brain, for example. Sensitivity of the eye cornea is enabled by a different nerve - ...
  • 7,989
8 votes
Accepted

Why can't the human eye focus blue light?

The same thing happens in photography when you see an image with colorful shadows of objects on it - this is called chromatic aberration. Check this wiki page if you're not familiar with. Now this ...
  • 3,078
8 votes

How many mega pixels does the eye have?

Short answer The total number of photoreceptors ('pixels') in the human retina is 63 million. Approximately 3 million of them transmit focused, color-coded information. Background In essence, each ...
  • 51.5k
8 votes
Accepted

Would the human body react faster to touch or sight

A "touch" or "haptic" sensation will be much faster due to several reasons: Haptic feedback can be processed without the presence of any higher-order cognitive processing, therefore meaning that the ...
  • 2,593

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