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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 "collect and save the effect of photons" over time, if you want to phrase it that way. That allows a camera to make images that our eyes never can, for example, of ...
29
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 thrive better in 'day mode' (i.e., photopic conditions).
To start with a controversial assumption, humans are diurnal animals, meaning we are probably, but ...
22
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 functional when you close them, only covered by the eyelids, you are able to see when light strikes your face.
21
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 masked lapwing clearly shows its nicitating membrane in action, where it covers the eye in a horizontal motion. This is analogous to blinking in humans, and the ...
21
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 going from bright ambient light to low-lighting conditions is caused by a process called dark adaptation. The visual system works on a huge intensity scale. The ...
19
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 of various size, shape, consistency, refractive index, and motility within the eye's vitreous humour, which is normally transparent.
You can read the wikipedia ...
17
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 damage.
Question 2 - What use is cornea transplant to a completely blind person?
Answer: It depends. If the blindness is due to clouded cornea (several diseases ...
17
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-eye effect in humans was explained nicely by Yale Scientific Magazine, and I adapted the following text from that source:
The human eye can effectively adjust to ...
17
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 resolution) first increases from birth up until around 4-6 years. Note that in the following graph better acuities are represented by lower numbers (logMAR scale)...
16
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 red light. (reference)
Our tissue transmits red wavelengths of light very well, but it doesn't transmit blue or wavelengths of light towards the blue end of the ...
15
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 are kept for transplantation. Of course, this will not repair blindness in someone that has problems in other areas of the eye, but corneal transplants are ...
15
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 cones (photoreceptors detecting low wavelengths) of many species, including humans and cats, extends into the UV range (Fig. 1).
Fig. 1. Human cone absorption ...
15
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 scanning the "area of vision" and the body and head are supposedly also moving (willingly or not - nobody can freeze totally) so longer accumulation of data ...
15
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 opinion.
First off, in darkness we cannot focus on an object and our eyes will move. And even when we focus on a specific point there is always movement of the ...
14
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 Orthostatic Hypotension which, in term, results in a transitory reduction in the blood supply necessary for brain function. You experience a momentary loss of ...
14
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 periphery. You want to be able to respond quickly to a threat "in the corner of your eye" without needing to see the color of the threat.
This is nicely explained by ...
12
Infrared wavelengths are EM waves of longer wavelengths than visible light. Also, visible waves are more energetic than IR waves.
Because of this, Visible light has the ability to excite organic receptor molecules in our eyes called Rods and Cones. These molecules stimulate cell responses and in turn excite cell responses in our nerves called an Action ...
12
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 of output. So if there's a lot of stimuli they like, they will reduce their gain, and vice versa. It can be thought of as a form of fast time-scale homeostasis ...
12
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 eyes indeed have the highest relative amount of visibly exposed white sclera. The amount of visible sclera provides information about the orientation of the ...
11
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.
The cornea spends about a third of it's lifetime under closed lids. At night, the tear film remains intact and is continuously replenished. The inner aspect of ...
11
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 the age-matched groups. Participants with light-blue-colored iris showed significantly higher values for intraocular straylight than those of the other groups.
...
11
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 very still for it to work.
Go take one of the time lapse pictures, like anongoodnurse's answer posted. The shutter is open for quite some time (her picture ...
10
First of all, I should correct some points that were misunderstood.
Don't change the question because this will lead to confusion.
"The way the lens becomes flat is by using spring-like connective tissue called choroids that pull it taught."
In classic ophthalmology you don't need to think about choroid in direct relation to accommodation: choroid is a ...
10
First of all, I should quote the sentence from the MOST reliable ophthalmology sourcing in the world - American Academy of Ophthalmology:
Section 11 - "Lens and Cataract"
"The equatorial diameter of the unfixed human lens measures 2 mm at 12 weeks and 6 mm at 35 weeks. Both the growth and the maturation of lenticular fibers continue throughout life." The ...
10
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 light that would have normally been absorbed.
10
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 to explain. It is a result of light adaptation in your retina responding to different levels of light being received by each eye.
Background
The level of ...
10
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 (like breathing.)
If you define resting state as that which the lids would assume without any innervation, then the resting state of the eyelids is semi-open. ...
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