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EyeEyeistheorganofvision.Itdetectslightandconvertsitintoimpulseinaneuron.
Thatimpulsetravelstothebrainwhereimageisformed.Howeyeevolvedwasasubjectofsignificantstudy.Firsteyeswerejustsimple
fotocells.Theytheyevolvedinsuchwaythatarealiftedaroundthosefotocells.Throughtimethatformedwhatisnowknowsaseyesocket.Furthermoreeyesocketwasfilledwithtransparentliquidandthatishowmoderneyestarted.AsDarwinputit,itisoneofthemostremarkablecreationsofevolution.
Eyesareadaptedtotheenviromentandliferequirementsoftheorganismtowhichtheybelong.Therearemanytypesofeyessuchascompundeyesfoundininsects,eyesadoptedtonightvisionsuchastheeyesofcats,eyesforfasttrackingofprayfoundonspeciessuchaseaglesandhawks.
Humaneyehasalotofchemicalcompoundscalledrodsandcones.Rodsdetectlightingeneralandcreatemonochromaticpicture.Conesdetectcolorofthelightandthenbraincolorsthepictureacordingly.Furthermorehumaneyeiscapableofchangingthefocallengthofitsaparatusandthusiscapableofrefocusingimageatanydistance.Eventhoughhumaneyesarefairlygood,theycarrysomeEvolutionarybaggage.Thatiswhyhumaneyehasthirdeyelid.Somethingweseehighlydeveloppedwithsnakesandcats.Itisusedtokeepoureyesmoist.Otherflawofhumaneyeisthatitisblindononespotwhereopticnerveconnectstotheeye.
Eacheyeiscontrolledbysixmuscles.Thosemusclescontractinsuchwaythateyealmostnevermovesleft,right,upordown.Itonlyrotates.Thatcanreallybenoticedwhen people fall asleep, as then they enter REMstage. That stands for rapid eyemovement.Duringthatstageofsleepoureyesrepidlymoveinalldirections.Ciliarymusclesaroundtheeyescompresstheminsuchwaytochangetheirfocallength.Thatenablesustousethemtolookfaraway,andalsoreallyclose.Humaneyecanfocusupto20cmforlongtime,withoutputtinganystrainontheeye.
Humaneyehasfieldofview(shortenedFOV)ofabout95degreestoleftandright.TodownFOVis75degreesdownand60degreesup.Peripheralvisionisupto180degreestoleftandright.EventhoughourvisionhashighFOVwecanonlyattaininformationfromsmallcenterpieceofaround1215degreesaroundthecenter.
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