Yleiset ominaisuudet
Theeyeisnotacompletesphere,butafusedtwo-pieceunit.Thesmallerunitisinthefrontandhasalargerarc,connectingthepartcalledthecorneawiththepartcalledthescleraofthelargerunit.Theradiusofthecornealsegmentisusually8mm(0.3inches).Thescleramakesuptheremainingfive-sixths,withatypicalradiusofabout12mm.Thecorneaandscleraareconnectedbyaringcalledthelimbus.Theiris-thecoloroftheeye-anditsblackcenter,thepupil,sincethecorneaistransparent,itreplacesthecorneaasthevisiblepart.Becauselightwillnotbereflected,acurvaturemirrorisneededtoviewtheinsideoftheeye.Thefundus(thearearelativetothepupil)showsthecharacteristicsoftheopticaldiscsurface(opticpapilla),andallthelightfromtheeyepassesthroughtheopticnervefiberandleavestheeyeball.
Koko
Thedifferenceinsizebetweenadultsisonly1mmor2mm.Thesizeintheverticaldirectionisusuallysmallerthanthatinthehorizontaldirection.Itisabout24mmforadultsand16mmto17mm(about0.65inches)atbirth.Theeyeballgrowsveryquickly,attheageof3ithasgrownto22.5mmto23mm(about0.89inches).Bytheageof13,theeyeshavereachedtheirmaximumsize,withavolumeofapproximately6.5milliliters(0.4cubicinches)andaweightofapproximately7.5grams(0.25ounces).
Sävellys
Theeyeshavethreecoats,whicharecoveredbythreetransparentstructures.Theoutermostlayeriscomposedofcorneaandsclera,andthemiddlelayeriscomposedofchoroid,ciliarybody,andiris.Theinnermostlayeristheretina.Liketheretinalbloodvesselsseenfromtheeyemembranecurvaturemirror,itobtainscirculationfromthechoroidalbloodvessels.
Inthesecoatsareaqueoushumor,vitreous,andflexiblelens.Thewatersampleisaclearliquidcontainedintwoareas:theareawherethelensisexposed,andtheanteriorchamberbetweenthecorneaandtheiris.Thelensissuspendedbytheciliarysuspensoryligament(ciliaryzonule)composedoftransparentthinfibers.Thevitreousbodyandtheposteriorchamberoftheeyearecleargelslargerthantheanteriorchamberoftheeye,locatedbehindthelensandtherestofthearea,coveringthesclera,zonulesandlens.Theyareconnectedbythepupils.
Dynaaminen alue
Thestaticcontrastoftheretinaisabout100:1(thefocalratioisabout6.5).Whentheeyesmoverapidly(eyeballtremor),itrepeatedlymonitorsthechemicalsubstanceandgeometricpositionthatittouchestoadjusttheiristocontrolthesizeofthepupil.Whenfirstexposedtoadarkenvironment,ittakesabout4secondstoplungeintocompletedarkness;throughthechemicaladjustmentoftheretina(Purkinspageeffect),itusuallytakes30minutestofullyadapt.Thedynamiccontrastatthistimemayreachabout1,000,000:1(thefocalratioisabout20).Thisprocessisnon-linearandmultifaceted,soifitisinterruptedbylight,theadaptationprocessmustberestarted.Completeadaptationisdependentongoodbloodflow,sodarkadaptationmaycauseagreatburdenonbloodcirculation(anemia),whichseemstobeaffectedbyalcoholortobacco.
Theeyeincludesalens,whichisdifferentfromanopticaldeviceusedinanopticalinstrumentsuchasacameraandanopticallensthatappliesthesameprinciples.Thepupilisthediameterofthehumaneye;theirisistheaperture,likeabaffleintheaperture.Refractioninthecorneacreatesaneffectiveaperture(entrancepupil),whichisslightlydifferentfromthephysicalpupildiameter.Thediameteroftheentrancepupilisusually4mm,butitsrangecanvaryfrom2mm(f/8.3)inbrightplacesto8mm(f/2.1)indarkplaces.However,thevalueofthelatterdecreaseswithage,andthepupilsoftheeyesoftheelderlysometimesdonotexceed5-6mm.
Näkökenttä
Ihmisen näkökenttä on noin 95° ulospäin, 60° sisäänpäin, 60° ylöspäin ja 75° alaspäin.Näköhermon vauriopiste sijaitsee 12-15° temporaalisessa osassa, 1,5° vaakatasosta alaspäin, noin 7,5° leveä ja noin 7,5° leveä.
Katseliike
Ulkosilmälihakset
Pääartikkeli: Silmäulkolihakset
EacheyehassixgroupsofmusclestocontrolitExercise:externalrectus,medialrectus,inferiorrectus,superiorrectus,internaloblique,andexternaloblique.Whenthemusclescontractwithdifferenttensions,thetorqueexertedontheeyeballisalmostcompletelyusedtorotatetheeyeball,andonlyabout1mmofmovement.Therefore,theeyecanberegardedasasinglepointrotatingaroundthecenterpointoftheeye.
Nopea liike
Pääartikkeli: Nopeat liikkeet
Nopea liike,orshort-termREM,isusuallythemostactivedreamstatethatoccursduringsleepstage.Atthisstage,theeyesmovequickly.Theuniqueformofeyemovementisinvoluntary.
Eyeetremor
Pääartikkeli: Eyeetremor
Eyeetremorisrapid.Botheyesarecontrolledbythefrontallobeofthebrainandmoveinthesamedirectionatthesametime.Someirregulardriftsandmovementsaresmallerthantremorbutlargerthansaccades,andtheanglecanreach6arcminutes.
Mikro-sakkadi
(Microsaccade)
Pääartikkeli: Microsaccade
Evenifyoufixyoureyesononepoint,youreyeswilldriftThiscanensurethatindividualphotoreceptorcellscanbecontinuouslystimulatedtovaryingdegrees.Withoutchangingtheinput,thesecellswillstoptheoutputresponse.Inadults,microsaccadescausetheeyemovementangletobelessthan0.2°.
Vestibulaarinen refleksi
Pääartikkeli: Vestibulaarinen refleksi
Vestibulaarinen refleksiiswhentheheadismoving,theeyeswillmoveintheoppositedirectiontoTheimagemaintainsastablereflectionmovementontheretina.Forexample,whentheheadmovestotheright,theeyesmovetotheleft,andviceversa.
Sileän liikkeen jälkeen
Pääartikkeli:Flowingsmooth
Theeyecanfollowamovingobject.Thisfollowingisavestibularreflex,whichdoesnotrequirethebraintoprocessincomingvisualinformationandprovidefeedback,soitisnotveryaccurate.Althoughtheeyesoftenglancewithreflection,itisrelativelyeasytofollowobjectsmovingataconstantspeed.Adulteyescanfollowsmoothlymovingobjects100%smoothly.
Underlowilluminationconditions,unlessthereisanotherreferencepointfordeterminingthespeed,itisdifficulttovisuallyestimatethespeedofmovement.
Teoptokineettinen refleksi
Teoptokineettinen refleksiisacombinationofscanningandfollowingsmoothmotion.Forexample,whenwatchingamovingtrainoutsidethewindowfromthewindow,theeyescanbefocusedonthemovingtrainforashorttime(byfollowingthesmoothly)untilthetraingoesoutofview.Atthispoint,theoptokineticreflexworks,movingtheeyesbacktothepointwherethetrainwasfirstseen(viaglance).
Läheisyysvastaus
Close-upvisualadjustmentinvolvesthreeprocessesthatfocustheimageontheretina.
Vergence-liike
(Ryhti)
Whenacreaturelooksatanobjectwithbotheyes,theeyesmustrotatearoundaverticalaxis,sothattheimageTheeyecanprojectonthecenteroftheretina.Toseecloserobjects,thetwoeyesmustrotatecloser(convergence,whilelookingatfartherobjects,thetwoeyeswillrotatemoredivergent.Theexaggeratedconvergenceiscalledthecross-viewmethod(forexample,focusingonthehumanNose).Whenlookingintothedistance,or“startingtoseenothing”,theeyeswillneitherdivergenorconverge.Theconvergenceanddivergenceoftheeyesarecloselyintegratedwiththeadjustmentoftheeyes.Undernormalconditions,changethefocusoftheeyestowatchForobjectsatdifferentdistances,theeyeswillautomaticallyadjustandconvergetochangethefocusoftheeyes.
PupilCompression
Theedgeofthelenscannotdeflectlightasclosetothecenterarea.,Sotheimageinthelenswillhavesomefuzzyedges(sphericalaberration).Filteringoutthesurroundingsandonlylookingatthecenterofthelightcanminimizethesphericalaberration.Intheeye,whentheeyewantstofocusonacloseobject,Thepurposeofthepupilistoblockthesurroundinglight.Thepupilhasadualpurposeforthiswork:toadjustthebrightnessoftheeyeandreducethesphericalaberration.
Linssin säätö
ChangethelensThechangeincurvatureisadjustedbytheciliarymusclesthatsurroundthelens.Thesereducethediameteroftheciliarymuscles,relaxthecruciateligamentfibers,andallowthelenstorelaxintoamoreconvexlens.Thegreaterthecurvatureofthelens,thestrongertherefractionandwillThelightemittedbycloserobjectsismorecloselyfocusedontheretina.
Ikääntyvä vaikutus
Therearemanydiseases,mentalandphysicaldisorders,andage-relatedfactorsthatwillcausetheeyesandsurroundingstructuresChangesoccur.
Thechangesintheeyeswithagecanundoubtedlybecompletelyattributedtotheagingprocess.Manyphysiologicalandstructuralprocedureswillgraduallydeclinewithage(aging).Withaging,visualqualityDeteriorationisthesolecauseofeyediseaseandaging.Althoughtherearemanyeyechangesthatarenotrelatedtodisease,themostsignificantfunctionalchangeseemstobeadecreaseinpupilsizechangesandadeclineintheabilitytoadjustthefocallength(presbyopia).Pupilcontrolstheamountoflightthatcanreachtheretina,thepupilThedegreeofexpansiondecreaseswithage,resultinginasignificantdecreaseintheamountoflightreceivedintheretina.Comparedwithyoungpeople,theelderlyoftenwearmedium-densitysunglasses.Therefore,foranyvisualguidancethatneedstobeilluminatedtoseeForcleardetails,theelderlyneedextralighting.Certaineyediseases,suchasherpesandgenitalwarts,canbetransmittedfromsexualactivity.Ifcontactoccursbetweentheinfectedareaandtheeyes,sexuallytransmitteddiseasescanspreadtotheeyes.
Withaging,awhiteringdevelopsaroundtheedgeofthecornea,calledtheoldagering.Therelaxationcausedbyagingmakestheeyeandfacetissuesdroopandtheeyesocketfatatrophy.Thesechangesarerelatedtoseveraleyeandfacediseases,suchasItisvalgus,varus,saggingeyelids,andsaggingeyesandface.Thevitreousgelundergoesliquefaction(retrovitreousdetachmentorPVD)anditsopacity—visiblefloaters—increasesinnumber.
Variouseyecareprofessions,includingophthalmologists,optometrists,andopticiansareinvolvedinthetreatmentofeyeballandvisualdisorders.SnellenchartisakindofAneyechartusedtomeasurevision.Theresultsoftheeyeexaminationcanallowtheophthalmologisttoprovidethecorrectlensofthepatient'seyeglassprescription.Someeyediseases,includingmyopia,whichaffectsone-thirdofthepopulation,andhyperopia,whichaffectsone-quarterofthepopulation,andpresbyopia,whichlosesfocusduetoaging,arerecommendedtowearcorrectivelenses.
Ammattilaiset
Thereareenoughreasonsforthecomplexityofthehumaneyetobecaredandtakencareofbyprofessionalphysiciansotherthangeneralpractitioners.Theseexpertsoreyecareprofessionalshavedifferentfunctionsindifferentcountriesorregions.Eacheyecareprofessionalcanusuallybeclassifiedintooneormoreofthefollowing(thatis,insomecases,throughthelens,theophthalmologistcanperformsurgery;andthisisusuallytheresponsibilityoftheoptometrist)typeofprofessionalResponsibilities:
Silmälääkäri
Optinen oikomislääkäri
OptometriaOptikko
Optisten instrumenttien valmistaja