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Lecture 10

lecture 10

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Doug Mac Kay

10 Eyeball and RetinaOctober 01 2007Visual system takes up a lot of space in the brainPhotoreceptors hyperpolarize when stimulatedImages are turned backwards and upside down on retinaEyeball OpticsCamera modelpupil as aperture lens retina as filmpinhole pupilentire depth of field perfectly focused on retina for all objects in the field whether far or nearoone ray of light from every direction enters the eyeballdilate pupilrequire lens to refocus divergent beam of lightLens accomodationCorneal refraction is 43 dioptersfixedoDoes a lot of refocusing divergencelens refraction adjustable 1326 dioptersorefocuses image onto the retinafine adjustments for the actual distance of the object from the eyeballamount of refocusing accommodation depends on how far the object is from the eyeballothe farther the object is from eyeball the less divergence and the less focusing power are needed from lens thinner lensodivergent beam of light from close objects is largeneed thick lens to refocus near objectsciliary muscle pulls on lens perimeterciliary muscle relaxedlens pulled taut ocreates tension in suspensory ligamentogood for distance visionciliary muscle contractedlens relaxes and thickens osuspensory ligament relaxesogood for near visionRetinawhere photoreceptors can be foundMultiple layers of neurons to detect lightphotoreceptors are farthest from incoming lightoprotected by pigmented epitheliumcontains melaninblackprevents reflection to the front of the eyeballlight rays pass through all retinal layers via light channels between columns of cellsin fovea all layers of neurons are pulled away to expose photoreceptors1
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