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 ...
Bryan Krause's user avatar
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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 ...
AliceD's user avatar
  • 52.3k
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 ...
Bryan Krause's user avatar
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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 ...
Bryan Krause's user avatar
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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 ...
Bryan Krause's user avatar
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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 ...
Beastly Gerbil's user avatar
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 ...
bandybabboon's user avatar
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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 ...
adjan's user avatar
  • 2,106
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 ...
theforestecologist's user avatar
13 votes

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 ...
Neil_UK's user avatar
  • 231
12 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 ...
Gwen's user avatar
  • 883
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 ...
anongoodnurse's user avatar
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 ...
Anon's user avatar
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9 votes
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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 ...
AliceD's user avatar
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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 - ...
Jan's user avatar
  • 8,049
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, ...
bandybabboon's user avatar
  • 10.3k
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 ...
AliceD's user avatar
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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 ...
Ebbinghaus's user avatar
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8 votes
Accepted

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....
Luboš Motl's user avatar
8 votes
Accepted

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 ...
Roland's user avatar
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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 ...
Oosaka's user avatar
  • 3,245
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 ...
Bryan Krause's user avatar
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8 votes
Accepted

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 ...
Bryan Krause's user avatar
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8 votes
Accepted

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 ...
John's user avatar
  • 14.3k
7 votes
Accepted

How can alcohol cause blindness?

Methanol is rapidly absorbed not only after oral ingestion but by inhalation or after cutaneous exposure and becomes oxidised in the liver to formaldehyde and to formic acid, metabolites which are ...
Margus's user avatar
  • 186
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 ...
Deepak's user avatar
  • 173
7 votes
Accepted

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 ...
theforestecologist's user avatar
6 votes
Accepted

What causes the bright flash of light when poking my eye?

Short answer Pressure phosphenes are believed to be induced by stretch-induced activation of retinal ganglion cells. Background Flashes of light (phosphenes) due to pressure on the eye ball are ...
AliceD's user avatar
  • 52.3k
5 votes
Accepted

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 ...
Remi.b's user avatar
  • 68k
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 ...
Kawin M's user avatar
  • 403

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