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 ...
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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 ...
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19
votes
Accepted
How deep under water can humans open their naked eyes without damaging them?
Crushing damage from pressure occurs due to pressure differences. Imagine you have a rigid container. If you have equal gas pressure inside and outside, the pressure acts on just the walls and the ...
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17
votes
Accepted
What is the minimum light intensity that a human eye can detect?
From Hecht, S., Shlaer, S., & Pirenne, M. H. (1942). Energy, quanta, and vision. The Journal of general physiology, 25(6), 819-840.:
Direct measurements of the minimum energy required for ...
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14
votes
Accepted
Do colour-blind people see white?
It's definitely not white or grey generally, it's a mix of other colors, they often have low resolution of a particular color so that it's less visible rather than visible and grey.
Here's a page ...
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14
votes
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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 ...
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14
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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 ...
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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 ...
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13
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How deep under water can humans open their naked eyes without damaging them?
Goggles do not, cannot, protect eyes from pressure. The pressure on both sides of goggles should be nominally the same. In fact, divers tend to use a mask, which communicates with the nose, to be able ...
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11
votes
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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 ...
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10
votes
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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 ...
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9
votes
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Why can't we half-close our eyes?
The motion of the eyelid is driven by the levator palpebrae superioris, i.e. elevating muscle of upper eyelid, and it can be positioned to the intermediate, half-closed positions. At least I can do it....
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9
votes
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How are colors outside the standard RGB color scheme perceived?
This question is both biology and physics I think (I guess it's biophysics! :) so I feel it's worth answering here.
First, we must recognize the difference between wavelength, which is just a ...
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9
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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 - ...
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9
votes
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Why did we lose our fourth type of cone cell (in the eye)?
Let's be clear: most mammals, including basal primates, had only 2 cone cell types. Primates evolved a new cone cell becasue frugivores have a distinct advantage being able to distinguish reds and ...
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9
votes
How deep under water can humans open their naked eyes without damaging them?
Currently the record for the deepest dive wearing scuba equipment is 332.35m. The descent took only 15 minutes while the ascent lasted 13 hours 35 minutes.
Liquids do not compress, so the sinuses, ...
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8
votes
Accepted
Why are we able to differentiate between colored objects without the presence of light?
You seem to have many misconceptions about how we see and how that relates to light. I'll address them one sentence at a time:
Why are we able to differentiate between colored objects without the ...
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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 ...
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8
votes
Cerebral activity during exposure to non - visible light
Vision is based on a protein interaction with a molecule called retinal from vitamin A.
Wavelengths of light in the visual range cause a photoisomerization of retinal (a cis- to trans- change), which ...
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8
votes
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Comparion between machine vision & human vision
This is a potentially very very broad question, but I'll try to provide a simple answer that addresses the biggest misconceptions.
First of all, animal vision (and brains more generally) is massively ...
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7
votes
Do eye's muscle share the same nerve?
There are basically four different types of eye movements:
smooth pursuit (think about following a moving target with both your eyes, note how smooth the movement is)
saccades (think about moving ...
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7
votes
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How much light can pass through the human eyelid?
Short answer
About 0.79% of the light gets through on average, but there is variability across wavelengths and individuals. (variability between individuals seems to be correlated with density of ...
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6
votes
Accepted
What color does the other cone in Tetrachromacy correspond to?
According to Deeb (2005), there are two relatively common types of causes for tetrachromacy in humans:
The common Ser180Ala polymorphism, which results in two spectrally different red pigments in the ...
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5
votes
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Cerebral activity during exposure to non - visible light
[D]o we fail to see non visible light because our eyes lack the receptors for other frequencies, or does our brain receive signals that it just dumps because it has not developed to process the ...
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5
votes
What is the advantage of the inverted image on the retina?
There may be no advantage of the inverted image on the retina. But there is an advantage with the lens that refractes the image inverted.
Our eye lens is of convex in nature. Now lets see what is the ...
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5
votes
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Are all cone cells connected directly to the brain?
Are all cone cells connected directly to the brain?
No. Cones connect to ganglial cells.
Let's explore the numbers. Our eyes contain about 6 million cone cells, 90 million rods, and comparative ...
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5
votes
For humans, why is red the color of distinction rather than green?
The reason is more historical than biological.
Our own eyes are more sensitive to green light, and ambient light is mostly green (we are a diurnal being). If you start doing real botany, you will ...
5
votes
Accepted
What are the max angles of human eyeball rotation?
There shall be slight differences due to physiology. Nevertheless, the average vertical ascending angle is 25 degrees and descending angle, 30 degrees.
Within the x-y plane of which we assume to be ...
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5
votes
Why we see black colour when we close our eyes
The mechanism of sight is as follows (ref. 1). This was shown in the 1100s by Ibn al-Haytham (ref. 2), except the 4th step which may have been proposed by Galen in the 100s (ref. 3).
Light comes from ...
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5
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Would green light look different if blue and red cones were deactivated
The genetic condition you are describing is called green cone monochromacy (GCM). This condition is exceedingly rare because it requires the dual inheritance of tritanopia (absence of blue retinal ...
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