46
votes
Accepted
Why can't we see in low light if staring long enough?
For simplicity's sake, let's really reduce this to something like photography.
A camera's aperture can stay open indefinitely, allowing the plate (or whatever is receiving and recording light) to "...
- 24.3k
29
votes
Accepted
Are humans more adapted to "light mode" or "dark mode"?
A question that requires quite a lot of guts to ask on this site :) Nonetheless, and risking sparking a debate, there are a few arguments that spring to (my!) mind that can support the notion that we ...
- 51.2k
22
votes
How do we know the presence of light when our eyes are closed?
Short answer, your eyelids does not block all light. Since they are only a thin layer of skin, the light is able to pass through although not completely obviously. Since the eyes are still completely ...
- 362
21
votes
Accepted
How do birds deal with their eyes drying out at high speeds?
Birds have a body part known as the nicitating membrane otherwise known as the "third eyelid". This part has become vestigial in humans, where it remains as the plica semilunaris.
This image of a ...
- 9,314
21
votes
Accepted
Why do we go blind for a few seconds after switching off the light?
Short answer
The eyes need to adapt to the low lighting condition after you switch off the lights, a process called dark adaptation.
Background
The process behind the reduced visual function when ...
- 51.2k
19
votes
What are the floating translucent little objects called in the field of view?
I think you are talking about floaters (a.k.a. eye floaters or flying flies). You may want to have a look at this english.SE post in case you were not talking about floaters.
Floaters are deposits ...
- 67.6k
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-...
- 51.2k
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 ...
- 51.2k
16
votes
Accepted
How do we know the presence of light when our eyes are closed?
There are two reasons for light to appear red through the eyelids.
Eyelids get a rich supply of blood which contains iron (in hemoglobin). The iron in blood absorbs all colors of light but reflects ...
- 5,779
16
votes
Why can't we see in low light if staring long enough?
The simple answer is, that eye is not constructed such way.
The eye have much more "pixels" than "links" to the brain and sends in "preprocessed" image. Moreover the the eye is constantly moving and ...
- 261
16
votes
Why can't we see in low light if staring long enough?
The differences at the photoreceptor level have been addressed by others. The mechanical restrictions of the visual system were shortly hinted at by @gilhad et al., but deserve more attention in my ...
- 51.2k
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
15
votes
Accepted
What portion of the electromagnetic spectrum do cats see?
Short answer
Spectral sensitivity of cats indeed ventures into the UV, but not beyond ~320 nm. Their maximum is likely similar to ours, i.e., ~750 nm.
Background
The spectral sensitivity of blue ...
- 51.2k
14
votes
Accepted
Dark veil when getting up too fast
It's caused by a sudden shift in the pressure needed to circulate blood to your brain which your body fails to respond to sufficiently quickly. This results in a sudden loss of blood pressure termed ...
- 6,811
14
votes
Accepted
Why can I see a light flicker when it's in my peripheral vision?
Your retina contains both rods and cones. Cones are color sensitive, slow, and concentrated near the center of your field of vision. Rods are "light" sensitive, fast, and concentrated near the ...
- 490
12
votes
What is the science behind the inaccurate perception of colors?
First recall that pink is white minus green, more or less.
Now, your perception can be explained by adaptation: Neurons try to control their gain (amplification factor) to have roughly the same range ...
- 3,045
12
votes
Accepted
What is the function of the human eye white?
Short answer
The relative large surface area of the white sclera in humans has been linked to an enhanced ability to detect eye gaze.
Background
The white of the eye is caused by the sclera. Human ...
- 51.2k
12
votes
Why can't we see in low light if staring long enough?
There's probably a theoretical capacity to do so. The brain is amazingly good at signal processing, and could probably pull off such a summation. However, there is a limit. You have to hold very ...
- 1,364
11
votes
Accepted
How does the cornea breathe during sleep?
As you noted, the cornea needs oxygen, yet it's not vascular. It needs to get it's oxygen supply from diffusion. In the daytime, diffusion occurs from air through the tear film covering the cornea.
...
- 24.3k
11
votes
Accepted
Does your iris color have an effect on your vision?
Firstly, note that "eye color" is actually iris color.
The person with a lighter iris will have more straylight compared to person with brown iris:
The graph represents Intraocular straylight of ...
- 5,620
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
Accepted
Why do dog's eyes glow green on a photo?
Dogs, cats, and many other mammals have a Tapetum lucidum which reflects light back through the retina to help with night vision. Humans don't have this layer. The tapetum is probably reflecting green ...
- 5,288
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 ...
- 24.3k
10
votes
Are humans more adapted to "light mode" or "dark mode"?
From experiments it seems you should better use dark mode if you want to prevent myopia:
Using optical coherence tomography (OCT) in young human subjects, we
found that the choroid, the heavily ...
- 201
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 ...
- 24.3k
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 ...
- 49.2k
9
votes
Accepted
Can a color-blind person see color with filter glasses?
Short answer
Optical filters can optimize color contrast, but never restore color blindness. Filters remove colors, they can never add something. However, glasses like this can prove helpful for ...
- 51.2k
Only top scored, non community-wiki answers of a minimum length are eligible