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. J

    How the Human Eye Works & Its Impact on Vision

    I can't understand how eye actually works. From what I understand when I look at 2 objects of the same size The object that is further is smaller in the final image because light rays reflected from it take smaller surface at the retina (Here B is smaller than A because rays take less surface at...
  2. B

    Understanding the Human Eye: Exploring Focal Length and Retinal Distance

    I never could understand this: the lens focuses light onto the retina so shouldn't the distance between the lens and the retina be the focal distance? It does not seem to be the case while I was trying to look around for the answer on the internet. And since light is focused on the retina, the...
  3. gracy

    Eye donation?What actually is donated?

    My teacher said eye donation is actually cornea donation.So,it doesn't mean if the donor had green eyes ,the recipient would get green eye after donation.Because iris is not donated which is responsible for color of eyes.
  4. C

    MHB Conditional probability: Eye color of sibling

    Ok I am really stumped and have no clue what I am missing...Here is the scenario. We have a mother and father who can be either $BB$, $Bb$ or $bb$. The probability for both is:$$P(BB) = P(bb) = \frac{1}{4}$$ $$P(Bb) = \frac{1}{2}$$For the child one gene of the mother and one from the father is...
  5. RaulTheUCSCSlug

    Unraveling the Mystery of Strained Eye Magnification

    Homework Statement This is not really a homework problem but I wanted to figure out how to derive the equation for a strained eye which is $$ M= (N/f) $$ where N is the object distance from the normal near point, and f is the focal length of a magnifying glass. But then, this is for a relaxed...
  6. P

    What is a Eye Diagram - create it in Python

    I am self learning Python and developing Communication signals concept by coding programs. But I am not sure how to develop Eye Diagram code in Python - cause I do not know the formulas / concept to do so - say I have a signal bits like - 1 1 1 0 0 0 1 1 So what formulas of concept I should...
  7. Calpalned

    Eye Color Evolution in Hominids: Comparing Chimpanzees and Humans

    8) Chimpanzees have much less visible white sclera than humans. That is, their eyes are basically just black and brown. As a result, what do scientists think the eyes of hominids looked like?
  8. Suraj M

    Eye and vision during low intensity

    This is something that i noticed.i.e., it happen to me, when i went to my teacher to ask him why it happens he actually didn't believe me, i guess maybe because he was a physics teacher! Consider a room with\ all the lights switched off, let their be a far off light source which is very weak...
  9. Suraj M

    Eye & Blind Spot: Is it Median or Lateral?

    most books I've referred state that the blind spot is median and lateral to the fovea...isn't this wrong? the fovea is the posterior pole itself then the blind spot can't be median .. and also is the blind spot a bit above or a bit below the posterior pole??
  10. B

    How does eye strain affect the length of the eyeball?

    Ever since I learned that short-sightedness is due to the eyeball being too long, and far-sightedness is due to the eyeball being too short, I've wondered what the point of avoiding eye strain is. How could straining the eyes possibly have the effect of changing the length of the eyeball? By...
  11. T

    Can the naked eye change the outcome of the double slit experiment?

    Are there any actual experiments that have been made where it has established if the naked eye can kill the interference pattern on the detector screen in the double slit experiment, that is, can the naked eye somehow function as a detector in this experiement? Let me give an example to clarify...
  12. M

    Image seen by human eye through a convex lens

    Greetings, I don't have a magnifying glass/convex lens otherwise I would try to confirm this by experiment. Maybe I'll get one soon but to get things started. Let's say you have an object, with its own light source, and a convex lens with focal point f. The object is beyond 2f away from the...
  13. J

    Does anyone know of a simple eye simulator? (geometrical optics)

    I'm looking for a "simple" calculator, most likely a matrix based thing, to allow me to work out the size of an image projected on the retina by an object of a given size some distance from the retina. being the eye, the thin film approximation is no good (i.e. if I have an object 3cm from the...
  14. N

    Plano-convex vs Double-convex (fly's eye) cylindrical microlens array

    I am trying to find out if I could substitute a Plano-convex cylindrical microlens array with a Double-convex (fly's eye) cylindrical microlens array for laser beam homogenization in 1 dimension. Assuming that the lens parameters are the same, how would the quality of performance be affected...
  15. L

    Optics: how to make eye focus in distance?

    Hello! I have a theoretical & practical question. Theorecical: I noticed that when I turn on my smart phone camera application and look 'through it' on some distant object, holding smart phone 30 cm from my eyes, then my eyes are focused on 30 cm and not in distance. Is there a way...
  16. V

    Light converging inside the eye

    Does all the light entering our eyes converge to a single point on the retina (assuming minimal aberration)? If this is true then that means that only a tiny point is exposed to light inside the eye so it will hit and activate a single cell (unless the cells are much smaller than the point of...
  17. JJBladester

    Probability of hitting a bull's eye

    Homework Statement I'm studying for the FE exam and it's been a while since I've done some of the more basic math. One of the practice problems for the math section states: "A marksman can hit a bull's-eye from 100 m with three out of every four shots. What is the probability that he...
  18. Psinter

    Temporary blazing fast eye movements when thinking

    I was sitting beside my friend and I asked myself a question out loud which required scanning a mapped list (numbers-names) to find the answer. She heard and tried to help. I looked at her eyes while trying to find the answer myself and suddenly her eyes moved very quickly from center to right...
  19. thankz

    What is the meaning of the eye on the dollar bill?

    why do we have an all seeing eye on the dollar bill?
  20. T

    Can't actually see anything through the eye piece

    Heya peoples, Our son Josh has just turned 9 years old and he asked if he could have a telescope for his birthday! So we have bought him an Astronomical Telescope OECSYAZ2D114/F900, Dad sat down and set it up with him and all looks great...but we can't actually see anything...
  21. I

    Understanding Archery Risks: RSI & Eye Strain

    Homework Statement Each year, 5.7% of archers develop repetitive strain injury (RSI) in their arm. Each year, 3.6% of archers develop problems related to eye strain. However, 91.2% of archers develop neither. (a) Formally define sensible event notation, and summarise the information in the...
  22. P

    Eye Resolution: Calculating the Limit and Overcoming Obstacles

    Homework Statement The pupil of the human eye is normally around 5mm in diameter. A person with 20/20 vision should be able to read letters 9mm high at a distance of 20m, while in Chapter two of The Two Towers Legolas can resolve objects of around 10cm size at a distance of five leagues...
  23. M

    How Long Would a Photon Perceive Its Journey Across the Universe?

    Time in the "eye" of a photon Dumb question...but thought I'd throw it out there. So, ever since I was a little kid of 6 or so, I loved to look up at the sky. I knew all those stars were just suns. I also knew I was looking back in time, many thousands to millions of years, since all the...
  24. V

    Smallest Difference in Wavelength the Human Eye Can Notice

    Hello - I'm having a difficult time finding this answer anywhere else on Physics Forums. I'm curious if anyone knows, or can figure out, the smallest difference in wavelength that the human eye can notice. For example: Can the human eye detect if a light changes from 568nm to 570nm?
  25. T

    Refractive Eye Surgery: Physics or Electrical Engineering?

    Hello everyone, I am a freshman physics and computer science student thinking about what I want to do after I graduate. I have always been obsessed with the eye and its functions. I would like to get into refractive eye surgery machine building/research, specifically focusing on the laser in...
  26. G

    A hypothetical question about seeing an atom with the naked eye

    This is only hypothetical, but bare with me. I did some searching on the interweb and found out that a drop of water has about: 1.67 × 10^21 molecules (Source: http://wiki.answers.com/Q/How_many_water_molecules_are_in_one_drop_of_water) Also, the amount of protons and neutrons that can...
  27. T

    Internal visualization (mind's eye), theoretical systems, and belief

    So I have a question or two that I've wondered about for a while and am hoping that this is the right forum to (maybe) get some answers. The thing I've been wondering about is how important the visualization process is in dealing with more abstract, theoretical problems, especially as it...
  28. V

    Solving Human Eye Problem Homework w/o Quotes

    Homework Statement A) Under optimum conditions, the smallest black dot that can be seen subtends an angle of 2.3 x 10-6 rad. If a dot is viewed at a distant of 0.25 m, the near point of a normal adult, what is the smallest diameter it can have and still be seen? B) The maximum resolution is...
  29. L

    How does the eye detect the angle of incidence?

    I don't really know too much about the human body, but this is my rough understanding of how vision works: light comes from a source, like the sun, it hits an object, and then if it's of the right frequency it's reflected by the object and then enters one of your two eyes, where it is refracted...
  30. skyshrimp

    Exploring the Cat's Eye Nebula's Activity

    I'm just learning about space. The Cat's Eye nebula looks very energetic at the core. I can see what looks like plasma firing off chaotically from the center star. If this was video footage, would what we see in this still Hubble photo move rapidly (like solar flares seen in footage...
  31. E

    How is a uniform image formed in the human eye?

    I was wondering how a uniform image is formed. If the eye is a point then I can visualize how an image is formed. But the eye isn't exactly a point. So don't light rays from all angles hit all spots on the retina? How is a uniform image formed? For example if we're looking in a plane mirror, we...
  32. genxium

    Definition of View Angle of Human Eye ?

    Definition of "View Angle of Human Eye"? I've been told (since high school I think) that "view angle" in a 2-dimensional plane is approximately (distance to the object/object's length). The assumption is that I'm viewing an object AB of length L, basically a segment in a 2-dimensional...
  33. turbo

    Eye Appt Today: Unbearable Fragrances & Unfair Treatment

    I had an eye appointment this morning with a couple of doctors that I have previously worked with. Unfortunately, the staff continues to wear cosmetics and fragrances and I have been in misery all day. Migraines, COPD, and inflamed arthritis are not fun. I worked with many of those same...
  34. T

    At which distance can you see Saturn's ring with a naked eye?

    At which distance can you see Saturn's ring with a naked eye? I guess you would not be able to see it from Mars?
  35. F

    Nyquist frequency of human eye.

    I'm designing a monitor and I've been getting various answers to this, seems to really depend. I've gotten everything from 10-120Hz.
  36. Z

    Comparative Analysis of Bionic Eye, Human Eye, and Camera

    Basically I have to make a comparison matrix of the bionic eye, the human eye and the camera. I want to sound scientific so I thought I would check what you guys think I should use as properties in the matrix?? Please thankyou :)
  37. T

    Eye of Moon: Planet Orbiting a Double Star

    If you had a planet orbiting a double star and the planet had a moon similar to Earth's moon. Would it result in an eclipse that looks like the eye of a cat/snake? Wondering for a SF/F book project where that world's religion would hinge upon this phenomena.
  38. R

    Find Photons per second on the eye from a source a distance away

    Homework Statement A typical incandescent light bulb emits ~3x10^18 visible-light photons per second. Your eye, when it is fully dark adapted, can barely see the light from an incandescent light bulb 10 km away. How many photons per second are incident at the image point on your retina...
  39. M

    2D becomes 3D when looked at by one eye

    When I was about 25 I noticed that a 2D photo appeared 3D when looked at through a magnifying glass. First I thought it depended on the lens, but then realized it was because I looked at the picture by just one eye - exactly as the camera lens had seen it in reality. I.e. there is much 3D...
  40. C

    Maintaining eye contact when absorbing information?

    Hi, In general maintaining eye contact talking with people creates a sense of connection, but how do you feel about maintaining eye contact when listening to complex instructions? I often find it hard to maintain eye contact if an instructor is telling me something complex (such as...
  41. S

    Why is Mars so easily visible to the naked eye?

    I have been trying to figure out why I can see Mars, by eye, even when it is very close to a bright, almost full Moon. Firstly, Mars at its closest to Earth only has an angular diameter of less than 1/2 an arc minute, while the accepted limit of resolution of the eye is 1 minute. That equates...
  42. C

    Does a Convex Lens Cause Eye Heat When Viewing a Light Source?

    I was just wondering if a person wearing convex lenses looks at a light source... Will excess heat be generated in his eyes? As it is a converging lens.. Thanks!
  43. F

    Colors and eye sensitivity

    The color coordinates of displays for portable electronics such as laptop computers generally provide smaller color spaces than for television. Battery power is a critical limitation on the light sources used for the display and maximum display brightness is desired. Explain why a reduction in...
  44. O

    Diffraction limite of the human eye

    Calculate the diffraction limit of the human eye, assuming a wide-open pupil so that your eye acts like a lens with diameter 0.8 centimeter, for visible light of 500-nanometer wavelength. Is there a formula for this? There are two other parts to this question, but if I get this the others...
  45. N

    Magnifying Glass and Eye Glasses Comparison

    Do glasses work in the same way that a magnifying glass does. They take light and focus it onto a point? If a magnifying glass can burn an ant, do eye glasses burn our eyes to a certain degree? Could it just be that eye glass wearers don't stare at the sun? I hope you guys understand what I...
  46. H

    Why is virtual image not seen when a defective eye is corrected?

    Hello Everyone! I have a question related to the ACTUAL APPEARANCE of the virtual image/object formed when a person wears a lens. When a lens (spectacle) is used for correction of vision to make the rays meet at retina, my book says a virtual image seems to form before the lens. This takes...
  47. shounakbhatta

    Can the Sagittarius and Canis Major Dwarf Galaxies be Seen with the Naked Eye?

    Hello, If I am not wrong, I think that no galaxy can be viewed from Earth with naked eye, right?
  48. J

    Probabilities of archers A and B hitting the bull's eye

    Homework Statement Two archers A and B take turns to shoot, with archer A taking the first shot. The probabilities of archers A and B hitting the bull's eye is 1/6 and 1/5 respectively. Show that the probability of archer A hitting the bull's eye first is 1/2. Homework Equations...
  49. S

    Eye of the storm at Saturn's north pole

    Hi! I'm really excited about recent APoD picture, which shows Cassini's photo of a gigantic storm on Saturn's north pole. They also have an animation! I can't wait for a colour picture and videos. Meanwhile, since I still didn't state the purpose of this thread, what are the inner vortex...
  50. C

    Better to stay outside the Hurricane or head inside the eye?

    Homework Statement Imagine the following. You and your best friend are at sea on your ship. Your ship is designed to withstand seas during 120 knot winds. You measure the winds outside your ship at 30 knots. From satellite images and Global Positioning System (GPS) data, you pinpoint your...
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