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1、Light enters the retina on the side containing the optic nerves and travels through all the layer before reaching the receptors.,Retina,This animated cartoon illustrates how light (white dot) enters the retina on the side containing the optic nerves and travels through all of the retinal layers befo
2、re finally being absorbed by the photopigments in the outer segments of the receptors. A neural signal (yellow dot) is generated in the receptors which then travels through the neurons of the various retinal layers and finally travels out through the optic nerve up to the lateral geniculate nucleus.
3、,How light enters the retina and is transmitted out the optic nerve,Electron Micrograph of Human Visual Receptors,When looking at an object that is far away the lens is kind of skinny. What happens when looking at a nearby object?,Refraction,When looking at nearby objects the lens gets fatter, causi
4、ng the image of the object to be focused on to the retina in the fovea. What would happen if the lens did not get fatter ? By the way, the technical term for this change in lens shape is accommodation. We frequently call it focusing.,If the lens can not properly focus light on the retina, the image
5、will fall either behind or in front of the retina. Can you guess what would happen if the lens is too fat?,If you guessed that when the lens is too fat that light is focussed in front of the retina, you were right. Is there a remedy for lens problems that do not allow light to be properly focused on
6、 the retina? Sure.,Many people wear contact lenses to help image light properly on to the retina. Another solution is for a person to wear glasses. This places a lens in front of the eye not on the cornea as is the case with contact lenses. A recent solution is to use a laser to reshape the cornea.
7、this solution is possible only in some cases.,There are two kinds of astigmatism: 1. lenticular and 2. corneal. Astigmatism occurs when the surface of the cornea or of the lens is not perfectly smooth. If, for example, there is a small flat spot on your cornea the image in a certain direction on you
8、r retina will not be in perfect focus. If the figure on the right was constructed with all the radial lines of equal sharpness and contrast a person without astigmatism would see all these radial lines as perfectly sharp and with the same contrast. The diagram on the right has been fudged to illustr
9、ate how it might appear to a person with astigmatism. This condition can be corrected with a corneal contact lens or cylinder lens in a pair of spectacles.,Astigmatism,Contact Lenses,A very thin plastic lens, often flexible (soft lenses) floats on a layer of tears on the corneal surface of the eye.
10、These lenses can be of the permanent variety or disposable. The permanent variety need to be properly cleaned and cared for. The disposable are often worn continuously and the thrown,Corneal Contact Lens,away when removed. Note how the bottom edge of the lens is against the lower eye lid. If the wea
11、rer looks down, the lens is pushed up a little. This trick can be used to provide bifocal contact lenses. These lenses have different powers in the center than in the periphery. When the wearer looks down to read the lens is moved to a new position to facilitate seeing sharply at normal reading dist
12、ances. If there is an irregularity on the cornea (astigmatism) it is automatically corrected by the combination of the tear layer and the contact lens.,A cylinder lens is different than a spherical lens which is what one normally sees in spectacles. Although a cylindrical component my be built in to
13、 that which appears spherical. As can be seen in the left diagram a cylinder lens has power only in one axis. In the left it is the horizontal axis. This lens does not refract light in the vertical direction.,Cylinder lens,Spectral Sensitivity Curves of Rods here are two examples showing the differe
14、nce between good and bad use of color. The Trick is to keep brightness differences large and to avoid color combinations that do not contrast well.,A comparison of the two color wheels shows which color combinations would be difficult to see. Graphics cause the most problems, but the colors can be e
15、conomically illustrated as text examples, below. The right-hand column illustrates how the left hand column might look to a color blind person.,Some examples of color combinations that are easily seen by a color blind person are shown below. These are illustrated as text examples but these principle
16、s are most important to keep in mind when preparing drawings, graphs, and figures.,cone,狗是色盲？,点击图片 播放视频,眼见为实？,马赫带效应,Mach bands,Boynton Illusion,Color Influences Distance Perception,Radiating Lines,Take two pieces of paper and place their edges as close as possible to both sides of one red diagonal. Note that the red square in the middle is the same as all the other squares on that diagonal. Now move your pieces of paper to expose main
