What is Eye: Definition and 268 Discussions

Eyes are organs of the visual system. They provide animals with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and convert it into electro-chemical impulses in neurons. In higher organisms, the eye is a complex optical system which collects light from the surrounding environment, regulates its intensity through a diaphragm, focuses it through an adjustable assembly of lenses to form an image, converts this image into a set of electrical signals, and transmits these signals to the brain through complex neural pathways that connect the eye via the optic nerve to the visual cortex and other areas of the brain. Eyes with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system. Image-resolving eyes are present in molluscs, chordates and arthropods.The most simple eyes, pit eyes, are eye-spots which may be set into a pit to reduce the angles of light that enters and affects the eye-spot, to allow the organism to deduce the angle of incoming light. From more complex eyes, retinal photosensitive ganglion cells send signals along the retinohypothalamic tract to the suprachiasmatic nuclei to effect circadian adjustment and to the pretectal area to control the pupillary light reflex.

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  1. DrClaude

    Stargazing Eye protection while watching a total solar eclipse

    I got myself some glasses for the upcoming solar eclipse, but they are very dark! They work fine for looking at the Sun in all its glory, but I suspect I won't ne able to see anything of interest during the eclipse. Does anyone have experience filtering out the harmful UV while still being...
  2. J

    How Does Flickered Light Affect Our Brain's Perceived Contrast and Brightness of Images?

    Bear with me this will be long, but everything here I feel is necessary to understand the context. I recently used a crt at varying refresh rates and noticed a few things that has made me question how the brain perceives colors on a display. First, is that my crt appears to have more color...
  3. L

    B How do I calculate the drop force on a cord and eye bolt?

    i have a question. I have set up an expierment and need some values. I have a round, 3d printed disk, 0.25 inches thick and 4 inches in diameter. In the center, i have a eye-bolt attached. I have hooked up a chain to the eyebolt and some weight to the chain. I have 40Lbs hanging right now and...
  4. L

    B Does light ever go from the eye to the image?

    You can see from the picture that the teacher has circled the arrows which shows light coming from image to the eye, and drew it in the opposite direction saying the light goes from the eye to the image. The marking scheme of this paper only says the correct direction does not specify which is...
  5. jtbell

    Longest Road Trip Since the Pandemic?

    I'm in Atlanta again (or rather, just outside it), on my longest road trip since my previous visit almost exactly three years ago, before the pandemic shut everything down. https://www.physicsforums.com/threads/mini-road-trip-dont-take-this-place-for-granite.983859/ I'm booked for three nights...
  6. Salmone

    I How does an eye reconstruct an image?

    I would like to understand the relationship between the image formed on the retina and the image reconstructed by the human eye. Let's consider this images: The object B forms the real image OB' while the object A forms the real image OA' on the retina. Second image: here, the object forms a...
  7. greg_rack

    Ranking "by eye" bi-material cross sections for strength/stiffness

    Howdy guys, Say we have been given the four thin-walled cross sections below loaded in pure torsion, where the material in black, titanium, has E=100GPa and the one grey one, aluminum, E=75GPa(no clue why Es are given, as I would have expected the shear modulus, G... maybe it is expected to use...
  8. kyphysics

    What is the smallest unit of measurement used that the eye can see?

    There are units of measurement smaller than our eyes can see, but that we use in science. But, what is the smallest one that we can see and work with regularly? I mean...on a traditional ruler, it'd be a millimeter, right? But, we can obviously go smaller - even if a ruler doesn't mark it...
  9. T

    Stargazing How can we see the ISS at 200 miles away with the naked eye?

    NASA says the ISS is 200 miles away. Planes fly at around 10 miles from the surface and we can't see them due limits to the angular resolution of the human eye. Given the inverse square law of light and the ISS being 20 times the distance to the plane, how is it possible to see the ISS?
  10. PainterGuy

    Medical How does human eye decode different geometric shapes such as circle?

    Hi, How does a human eye classify any shape as a circle, square, triangle etc.? Let's focus on a circular shape. Suppose we have a circle drawn in white on a black surface. The light falls on the retinal cells. I think the light falling on the retina will constitute a circular shape as well...
  11. L

    Does the human eye magnify objects?

    Does the human eye see things at the correct size or is there such a thing? I know one of my eyes sees things slightly smaller than the other, but ideally should the eyes biologically not magnifying or shrink anything at all?
  12. D

    Optical Where to look for a UV light that is invisible to the naked eye?

    Where to look for a UV light that is invisible to the naked eye? Essentially I want to buy a UV light that doesn't have that annoying blue glow, I just want the UV light that is invisible to the naked eye like infrared light. I read a bit about it and from what I read what I'm looking for is...
  13. NatanijelVasic

    3D Cinema Glasses: An Unsolved Personal Experience

    Many years ago I went to the cinema to watch Avatar in 3D, and was provided with polarising 3D glasses at the venue. I can't remember if it was my first 3D film that involved polarising projection technology, but it was certainly one of my first. In any case, the 3D effect worked and I got...
  14. S

    Imaging resolution for a microscope and eye

    Hello folks, I have the two following questions I'm working on: Q1 An optical microscope uses a lens with NA = 0.7 and a focal length of f = 20 mm. What is the smallest spatial distance that can be resolved if a wavelength of λ = 633nm is used? An iris is introduced in front of the lens with a...
  15. DarkMattrHole

    I Event Horizon Radius: Is it Constant?

    Let's say there is a black hole billions of miles away from earth, a hefty one such that a careless traveler could end up inside the horizon before noticing he'd been swallowed by the BH. Based on Earth observations the BH event horizon radius is r. We hop in a ship and go to a safe escape...
  16. George Jones

    Stargazing Spotting Comet NEOWISE with Naked Eyes: A Spectacular Visual Experience!

    It was clear all day yesterday, and the forecast was for mainly clear all night, so, at 11:00 pm, I set up scope for a visual session with Jupiter and Saturn before bed. By the time I was ready to align the scope, the sky was mainly cloudy, and Jupiter was not visible. i came inside to read...
  17. Spinnor

    Hurricane hunters spot 'stadium effect' inside Dorian's eye

    Hurricane hunters spot 'stadium effect' inside Dorian's eye amid 'extremely intense' storm, from, https://www.foxnews.com/us/hurricane-dorian-eye-hunters-stadium-effect-cyclone.amp?cmpid=prn_newsstand A collection of images and videos of the hurricane Dorian from...
  18. Graeme M

    B The Human Eye as a Detector in Double-Slit Experiment

    Trying to wrap my head around what the double-slit experiment is illustrating, it occurred to me that one could replace a mechanical detector with the human eye. I found that this was tested with what seems an elaborate test setup in 2016, and the result suggests that while an interference...
  19. Sophrosyne

    The physics of eye and skin color

    I was reading about why blue eyes look blue. After all, the human body does not create any blue pigment. It turns out, it's the same reason the sky is blue: the Tyndall effect. When there is minimal pigmentation, the first frequencies of light to scatter are the blue frequency waves. When there...
  20. S

    Physical explanation of eye contact

    Is it not fascinating that you can feel eye contact on such distances we do? What is it that we actually detect? I understand that the eye absorb light, it may be the starting point for the explanation?
  21. F

    I Human eye and its focal length range....

    Hello, The human eye has an average diameter of ##2.5 cm## and an optical power between ##60D## and ##64D##. An object can be brought as close as the near point which is about ##25 cm##. If ##d_{o}=0.25m## (object distance) and ##d_{i}= 0.025m## (distance to the retina), the optical power...
  22. S

    B What process allows us to 'see' lightyears of distance with the natural eye?

    Leavitt's Law allows us to determine how far stars are from us by calculating their variable magnitude of brightness. Please explain how it's possible then for us to see, with the 'natural eye', the distances from one star to another, from one point in the night sky to the opposite, that would...
  23. Nik_2213

    Parietal eyelid(s) 'across' or 'up/down'?

    Lizards, reptiles, tuatara and fossils with parietal 'third' eyes do not seem to have legacy bone attachments / processes for their third eye's lid muscles. In fact, IIRC, the 'parietal eye' seems 'inside out' and 'fixed' compared to said beasties' 'ordinary' eyes. Perhaps Vertebrae Eye 1.0 ...
  24. I

    Model electron movement in an electric field (Magic Eye tube)

    Hello there, I'd like to model a simplified version of a "Magic Eye" tube (e.g. without the amplification triode, and for a start, 2 dimensions only), or the visible display behavior. What I'm talking about: https://en.wikipedia.org/wiki/Magic_eye_tube#Operation Here is a nicer depiction of...
  25. R

    Relative eye safety of infrared and ultraviolet lasers

    My question is about the relative eye safety of infrared (##\lambda \gtrsim 1400 \ nm##) and ultraviolet (##\lambda \lesssim 300\ nm##) lasers. Both of these wavelengths are highly absorbed by the pre-retinal water content in the cornea, so they don't really penetrate into the retina. So one...
  26. M

    Can a photon travel slow enough to be seen by the naked eye

    Please see my attachment of a recent observation of light traveling through a medium. There is no source, just my observation The packets of light appear to be visible, distinct , moving at different speeds, and display the various colours for each wavelength. Is this normal / possible in a...
  27. navneet9431

    Is light eye colour dominant or recessive trait?

    Homework Statement A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not? Homework Equations Not Any The Attempt at a Solution...
  28. T

    Is the eye more sensitive to intermittent light/flashlight?

    Is the eye more sensitive to intermittent light/flashlight than to constant light , if both have the same intensity ?
  29. Zeynel

    What would make the human eye see more details?

    First let me tell you the context: There was this recently discovered tiny sealstone depicting warriors in battle measuring only 1.4 inches across. This piece contains incredible detail that modern human eye cannot discern without a mechanical aid. Read more at...
  30. Asmaa Mohammad

    Medical The power of the human eye's lens

    Hello, I read in my physiology book that when the ciliary muscle relaxes, the power of the eye lens decreases, hence we get the ability to see far objects. I am new to physiology, and when I googled "the power of the eye lens" I didn't find articles explain the sentence above simply. So I...
  31. BenAS

    B Is it possible to see sunspots with the unaided eye?

    This has been bugging me for a while, I'm not sure what I saw exactly. A few months ago there was some thin clouds blowing past the sun, obscuring it to the point you could easily look at the disk with the unaided eye. There was a dark spot, that looked like a sunspot as seen in filtered...
  32. T

    Differences between hand eye coordination and reflexes

    What are the differences between hand eye coordination and reflexes? So when one catches a ball, they must have a specific level of hand eye coordination and reflex / reactions in order to be able to catch the ball. What aspect of catching a ball is related to hand eye coordination and what...
  33. M

    Light and oxygen acting upon the eye and the lung during the process of Evolution

    Did the evolution of the eye include interaction/reaction with a specific frequency of light? Did the evolution of the lung include interaction/reaction with the air density, humidity, and temperature of its environment?
  34. A

    What Is the Smallest Spot Diameter the Human Eye Can Detect?

    Homework Statement The resolution of the eye is ultimately limited by the pupil diameter. What is the smallest diameter spot the eye can produce on the retina if the pupil diameter is 2.59 mm? Assume light with a wavelength of λ = 550 nm. (Note: The distance from the pupil to the retina is 25.4...
  35. N

    A Basic question about Head-Up Display and Near Eye Display

    I have seen built-in HUD in both a BMW and a Mini Cooper. In the first the windshield is used as the combiner while in the second they use a separate piece of glass located on the dashboard. The systems work by reflecting and magnifying a real image at least once in order to create a virtual...
  36. G

    I Steam punk, Field of view including the eye

    Sorry if I missed the answer in my search. I expect I'm not use the correct terms. I want to design a Galilean/opera glasses style steampunk monical mounted to my reading glasses. I already have a simple lens that I can swing in front of my one eye. When using commercial eyeglass mounted...
  37. R

    I If the observable universe was visible to the naked eye....

    What would the Earth's night sky look like? Would our eyes see any dark spots? Is there are way to calculate such a probability? This hypothetical is about the observable universe only. 93 billion light-years diameter, isotropic, visible light. Not sure what's the most appropriate tag for this...
  38. T

    Radius of Curvature to Correct Myopia

    Homework Statement A person's eye has a near point of 7 cm. The cornea at the outer surface of the eye has a refractive index of n_c = 1.376 and forms a convex shape with a radius of curvature of R_2 = 8 mm against air. The figure below shows the same eye with a contact lens (refractive index...
  39. Tareq Naushad

    How mirror/camera/tv work without human eye like system?

    Mirror/camera/TV etc. don't have a complex visual cortex system/perception like our eyes. Human eyes use rod,cone,neuron and above all perception of brain to make image. How come these devices create the same clear images/scenes at their surfaces by themselves without having the advance...
  40. B

    How advanced are spy drones used in the military and law enforcement?

    In this movie Eye in the Sky about drone deployment in the middle east. This is this small electronic beattle which can fly and has built in camera to spy inside houses. Is this technology real? Where can one get it? Should there be none, what is the smallest drone you saw that has good...
  41. W

    What Is the Correct Name for This Animatronic Eye Mechanism Part?

    Hello All. I'm searching for this part and also have video footage of it in motion. I cannot find it to finish the eye mechanism because I don't know what it's called. Can anyone tell me what it is? I would greatly appreciate it. Even companies dealing in such parts as well as metal...
  42. I

    How many neurons fire in an eye blink?

    I am wondering how many neurons would need to fire approximately in a human brain in order for the eye to blink, or for example, for a head to nod? And I am referring directly to just the motor act, not all the internal brain processes that might lead to an eye blink. And I am not necessarily...
  43. Mastico

    Special Ink invisible to the eye

    Greetings all, I am quite new to this forum so please forgive me if this is on the wrong thread. I recently purchased some reflective paint which sprays on clear and appears white/silver once light hits it at night. However I am looking for a type of paint that is invisible to the naked eye...
  44. kolleamm

    How do I find eye protection for my laser cutter?

    I recently received a laser cutter however, I cannot find anywhere not even in the manual what frequency it emits. It's a CO2 machine with a 180 watt laser. It's supposed to be able to cut metal. http://www.ebay.com/itm/121881769914 Can someone advise me on eye protection, I don't want to risk...
  45. S

    Image formation by convex lens

    What will happen if look at(or in the direction of) a distant object through a convex lens?
  46. J

    Particles with electric charges visible to the human eye?

    Are there any particles known in the Physics world with an either positive or negative charge that can be viewed by the human eye under LED light illumination and have an attraction/repulsion to magnetism?
  47. A

    Photo Eye Power: Current, Voltage, & Resistance Explained

    I was reading the specs on a photo eye and it states its current consumption 65 mA at 24v 120 mA at 12v both situations end up with roughly 1.56 VA of power...how does it draw more current with less voltage applied. If V=IR, the only way i see it is the resistance of the system must lower...
  48. B

    The Mystery of the Couple's Children: Eye Color Edition

    Hello, In the picture above a couple are shown with their children. Or are they actually their children? Is it possible for them, having green (?) and hazel (?) eyes, to get 1 child with blue eyes and 3 children with brown eyes?
  49. A

    Abt seeing the Andromeda Galaxy with the naked eye in future

    According to what I've read, the andromeda galaxy is approaching the milky way galaxy. Also, I've just recently discovered (on the net) that andromeda has a much larger subtended angle than the moon or sun. Hence, as it approaches it's angle subtended will keep increasing. I've also known that...
  50. wolram

    Can You Trust Your Memory as an Eye Witness?

    I bet most of you will fail this test, it just goes to show that an eye witness is not reliable witness, any way test your skill at memory and observation. http://www.youramazingbrain.org/testyourself/eyewitness.htm I am a very poor witness, now be honest with your score:biggrin: