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. C

    Why has no one seen Neptune with the naked eye?

    According to http://en.wikipedia.org/wiki/Apparent_magnitude" Neptune could be visible to the naked eye. Neptune's maximum brightness is magnitude 7.78 while the faintest star known to be observed with the naked eye is magnitude 7.72. But that star was only observed as a guide to observe the...
  2. D

    Number of photons emitted from a light bulb entering the eye

    Homework Statement A 100W bulb emits light of a single wavelength 6000*10^-10 m. If light spreads out uniformly in space, how many photons enter your eye per second if you are at a distance 1m from the bulb and the pupil diameter is about 1mm? Homework Equations E = hc/lambda The...
  3. C

    What is the spatial resolution of the eye for two red lights separated by 5cm?

    Homework Statement Two red lights are separated by 5cm, perpendicular to your line of sight. How far away from them are you if they can just be resolved with the naked eye? Homework Equations angular resolution =sin(theta)=1.22lambda / D spatial resolution = 1.22(focal length * lambda)/D...
  4. B

    Medical Does the human eye have a refresh rate ?

    Does the human eye have a "refresh rate"? This question probably seems ridiculous, but I have no background in physiology and I cannot find anything discussing it online or in my roommate's physiology textbook. I was wondering if anyone here knows whether the eye and brain processes...
  5. N

    Medical Bull's Eye Rash of Lyme Disease

    Recently I had Lyme disease and had perhaps the most stereotypical bull's eye rash ever. All medical people I met wanted to see it, and called their friends/coworkers over, took pictures, etc. But the rash still has me confused about the biology of it. The shape itself doesn't seem to make...
  6. P

    Can we predict the color that will be perceived by the eye?

    Hi,my question is the following: Supposing that we light up the same surface of an optical system (the eye) by two different monochromatic lights (each one characterized by a wavelength and intensity): Can we predict the color that will be perceived by the eye? Thanks for your help.
  7. DaveC426913

    Better in my eye than in my camera

    This was really cool in-person. I didn't take the time to check my camera settings, so it didn't record as well as I'd have liked. I am calling it a crepuscular rainbow. This is a pic of sun beams (crepuscular rays) streaming through the clouds - into a mist of raindrops. So, this tiny...
  8. P

    How Does a Change in the Power of Accommodation Indicate Vision Defects?

    how to know the defect of vision if power of accomodation of eye decrease or increase Homework Equations The Attempt at a Solution
  9. C

    ISS Toolbag visible with the naked eye now

    http://heavens-above.com/PassSummary.aspx?satid=33442&lat=0&lng=0&loc=Unspecified&alt=0&tz=CET It is losing height quite rapidly now, more than a kilometer per day.
  10. P

    Near & Far Point of Eye: Power of Lens & Max Distance

    the near point and far point of an eye are 35cm and 300cm respectively.what is power of lens so that the person can see objects at 25cm .with this lens what is the maximum distance he can see. f=xd/x-d p=1/f in m i could only solve the first part of the problem.p=1.14d...
  11. C

    Galaxies that can be seen with the naked eye

    http://en.wikipedia.org/wiki/Andromeda_Galaxy" http://en.wikipedia.org/wiki/Triangulum_Galaxy" http://en.wikipedia.org/wiki/Messier_81" I've only seen M31 with the naked eye. If I look at M33 through my 8 times 40 bino, then it doesn't look like something I could ever see with...
  12. C

    Eye Contact with Dogs: Friend or Foe?

    Hi, I was wondering about the following. A friend (biologist) once told me that looking a cat in the eyes shows aggression, whereas making eye contact with a dog creates a kind of connection or bond. However, a quick Google search seems to indicate that also in canines, direct eye contact is...
  13. V

    Can You See Color in Complete Darkness Due to Reflection?

    Assume I am standing in a desert at night (It's pitch dark). I have an opaque white object in front of me inclined at 45 degrees (see diagram). I now turn on a point light source next to me. http://img199.imageshack.us/img199/8945/lightt.jpg When I imagine the scene I feel I will be able to...
  14. A

    Focal Length of Eye Homework: C, F Calcs & Myopia/Hyperopia

    Homework Statement The diagram shows the eye of a person with normal vision looking at an object that is very far away. a) Determine the focal length of this persons eye. b) Later in this person's life, the focal length will change to between 2.1 cm and 2.3 cm. Will this person suffer from...
  15. W

    Can Eye Exercises Improve Vision Without Glasses?

    Many people I know advice me that doing eye exercises will help improve my vision and if I do them for quite some time, that I will not need glasses any more. Is this true? When I google this, all I get are advertisements.
  16. Y

    How Does the Human Eye Detect the Dimmest Starlight?

    hi there. there's an example in the book, but I'm having a little trouble here. Homework Statement Assume that the human eye can pick up as few as 9 photons/s in the visible range. Based on this, estimate the intensity of the dimmest star that can be detected by a night-adapted eye. What...
  17. L

    Understand Near & Far Points of the Eye: Lenses

    Homework Statement Could someone explain to me about the near point and the far point in the eye because I'm confused about the 25 cm for the near point and infinity for the far point. Also, like in problems like this: What eyeglasses would you prescribe for persons with the following...
  18. S

    The Next Naked Eye Comet: What to Expect & When

    When will the next comet apear for Earth viewers. I know that there is almost always a comet or two visable through a large telescope but when is the next one visable with the naked eye(I want to plan somthing import on that night.) . I wish i was around for comet Hale-Bopp but i was to young.
  19. Mk

    Help me get an eyelash out of my eye

    Last night there was something sharp in my eye and I messed around with it for a few minutes by blinking a lot popping my eyelid and rolling my eyeballs around. It didn't come out but when it got to a more comfortable position, I went to sleep, hoping it would automatically come out. Turns out...
  20. L

    At what distance can your eye no longer resolve two headlights?

    Homework Statement Once dark adapted, the pupil of your eye is approximately 7 mm in diameter. The headlights of an oncoming car are 120 cm apart. If the lens of your eye is diffraction limited, at what distance are the two headlights marginally resolved? Assume a wavelength of 600 nm and...
  21. J

    Exploring the Anatomy of the Eye: Oxygen Inside?

    Is the inside of the eye ball empty space? Or it is filled with oxygen?
  22. O

    Texas death row inmate pulls out eye, eats it

    http://news.yahoo.com/s/ap/20090110/ap_on_re_us/death_row_eye I can't believe they're going to execute him at all. If this isn't proof enough that he's insane, what would be? Here's his offender info: http://www.tdcj.state.tx.us/stat/thomasandre.htm
  23. Loren Booda

    What Causes the Range of Eye Colors in Humans?

    What biological reasoning explains the panoply of eye color in humans?
  24. L

    Why Does My Eye Sting at Night and Then Disappear in the Morning?

    This has happened to me about 4-5 times over the last year or so, but at random it seems, one night I'll wake up in the middle of the night and not be able to open up my left eye because of this unbearable stinging sensation (it's always my left eye too). If I even try to pry it open a little...
  25. Galileo

    What does this eye contact signal mean?

    I'm usually not too consciously aware of other people's body language. I don't want to read, then interpret, then act on the interpretation of someone's body language consciously. However, I've noticed something and I'm extremely curious as to what it means. Whenever I really want to create an...
  26. S

    Thought experiment: The 'perfect eye' (and a finite set of colours)

    Thought experiment: The 'perfect eye' (and a finite set of colours) Introduction: Human beings have trichromatic colour vision, our ability to distinguish different colours at different spectral frequencies, and wavelengths, of electromagnetic radiation, or combinations thereof, is...
  27. I

    Persistance of screen glow/image on the eye HELP

    Homework Statement Although the image in a television screen appears to change smoothly, it consists of 25 separate pictures every second. The production of a flicker free image is helped by: (i) PERSISTANCE OF SCREEN GLOW (ii) PERSISTANCE OF AN IMAGE ON THE EYE Explain how each of...
  28. K

    Determination of e/m of electron by magic eye method

    tell me how to perform this experiment and please post the figure of its apparatus.
  29. B

    Medical Can Laser Eye Surgery Correct Cross Eyes in Adults?

    Can laser eye surgery/anything fix cross eyes? 2 of my friends are cross-eyed and they're adults ty
  30. J

    Medical Losing vision in one eye and I have a crazy theory

    I'm still comparatively a young buck at 22, but I have been afflicted by a few things that don't show up for most people until much later in life. The one I would like to focus on is vision because it's the most annoying to me. I don't get checkups too often so as best as I can recall, I had...
  31. R

    What Eye Pieces Work Best for Beginners with a Meade DS114 Telescope?

    I've got a telescope (Meade DS114 -- reflecting, D = 114mm, F= 910mm, f/8) that I'm trying to get together again. We have several eye pieces still around -- H25mm, H12.5mm, SR4mm. We had a hard time locating objects (besides large things like the moon), so I'm wondering if I should try other...
  32. M

    Medical Questions About Contact Lenses and Laser Eye Surgery

    have absolutly no idea where to put this but ill put it here My eyesight is something like +6.25/+6.50 Now the eye man (optomotrist?) said that they only make contact lenses that go up to +6. I was wondering why this is? Also why can't long sighted people have laser eye sugery? Is there...
  33. N

    Microscope to view sample in focus with a completely relaxed eye

    Homework Statement A microscope has a converging lens (eyepiece) with focal length of 2.50 cm mounted on one end of a tube of adjustable length. At the other end is another converging lens (objective) with a focal length of 1.00 cm. When you place the sample 1.30 cm from the objective, what...
  34. R

    Medical Color Resolution in the Eye (blue and yellow)

    I'm having trouble finding information on why when you get far away from a piece of paper covered in yellow and blue dots (evenly spaced) the sheet eventually appears green. I know this has to do with color resolution but not much beyond that.
  35. D

    Photoelectric Effect and the human eye

    Homework Statement Under favorable circumstances the human eye can detect 1.0e-18 J of electromagnetic energy. How many 600-nm photons does this represent? (Modern Physics, Arthur Beiser, 6th Edition, Pg. 89) Homework Equations My answer is unreasonably low. My mistake is probably very...
  36. L

    Jury-rigging an electronic eye for a polarimeter.

    Been too busy with school to post here in a while, so of course I come back when I have a question about something! For some background, I'm working on a small study that, in part, is to characterize the optical activity of some biodiesel samples, one made from animal fat, the other from soy...
  37. Greg Bernhardt

    Eye Q product to teach speed reading

    Here is a product that claims it can teach you to speed read. http://www.infmind.com
  38. A

    What's the diameter of a fly's eye?

    [SOLVED] what's the diameter of a fly's eye? I'm a maths teacher and in a topic on units and 'big and small numbers', I've set my class various items to estimate, including the diameter of a fly's eye... Now it's driving me mad, I've spent hours googling to try to find out a reasonable...
  39. fluidistic

    Why do hypermetropian people not see reversed?

    My question is : Why do hypermetropian people not see reversed? According to wikipedia and many other sources, the light from a non reversed object arrives at the retina in the same sens, that is, non reversed. As we know, when interpreting images, the brain reverse the sens of the image on...
  40. S

    Eye of Ellipses: Photographing Magnetic Lines of Constant Scalar Potential

    Photographing Magnetic Lines of Constant Scalar Potential http://www.sendspace.com/pro/dl/3hchd6 This post is intended as an introduction to my paper, Photonic Dipole Contours. I have been asked to address some deficiencies in my paper such as background information and prior work...
  41. E

    A2 Health Physics Eye question

    Hello everyone, Really struggling to answer a practice exam question on the eye, and was wandering if anyone could help, here's the question: "The unaided eye of a student has a power of 59.0D when viewing an object at infinity. When using her spectacle lens, the near point is 25cm from her...
  42. B

    The Physics of Golden Eye Help

    1. Bond's usual gun of choice in every movie is a Walther PPK (except when he can get his hands on a machine gun which blows up more guys). A bullet like this has a mass of around 15g and leaves the gun at 288m/s. Calculate the kinetic energy in a bullet like this. 2.Aside...
  43. G

    Exploring the Mind's Eye: Visualizing without Light

    How does the mind's eye 'see' in the absence of light? Imagine a large empty room with a dresser at one corner. You walk up to the dresser and open the top draw. You see a red book and a box of matches. You light the book on fire and throw it on top of the dresser. I assume you could all...
  44. Evo

    Medical Tooth implanted in eye restores sight

    This is rather incredible. http://news.yahoo.com/s/afp/20080228/ts_afp/irelandbritainhealthoffbeat
  45. R

    (physics) Calculating eye diameter

    Is it possible to calculate the diameter of the eye from front to back when you what kind of glasses the person needs? Like if someone needs -2 type of glasses is it possible to calculate the eye diameter? If not would it be possible to determine someones eye diameter by determine the closest...
  46. E

    Optics & Vision: Understanding the Eye

    Hi. I'm new to this forum and wondered if anyone can help with this problem I have understanding how vision works. In some ray diagrams of the eye it show the rays converging to a point on the retina and on some diagrams it shows them converging before the retina and arriving at the retina...
  47. S

    Can a *gas* be visible to the naked eye?

    I found this: https://www.physicsforums.com/showthread.php?t=105106 But it the question was never really answered there. So I'd like to ask a *similar* question again. Are there any gases at STP, (without being "excited" or "liquefied"--see other topic, above) that are visible to the naked...
  48. Ivan Seeking

    Medical Can a human eye magnify an image?

    I once worked with a guy who had been hit in the head by lightning. As he described it, he was sitting on his porch and looking at a stop sign about a quarter-mile up the road. The last thing that he remembers - apparently at the moment of the strike - was the stop sign appearing to be...
  49. Evo

    News US, Japan eye China after ships barred

    Seems China is sending signals, but what is the message? http://news.yahoo.com/s/ap/20071130/ap_on_re_as/china_us_navy
  50. N

    Working of the Eye: See Virtual Images

    [b]1. Homework Statement Q: How does our eye see virtual images, considering that no light is emmited by a virtual image and our eye can see anything only when light from it reaches the eye? Examples: Image by a plane mirror, concave lens, convex mirror and by convex lens and concave...
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