Effectcells
Thehumaneyeretinaiscomposedofcountlessphotosensitivecells.Thephotosensitivecellsaredividedintorod-shapedcellsandcone-shapedcellsaccordingtotheirshape.Thereare7millioncone-shapedcells,mainlyThecentralareaoftheretinathatisconcentratedonthepupiliscalledthemacula.Therearenorod-shapedcellshere.Thefartherawayfromthemaculararea,thefewercone-shapedcellsandthemorerod-shapedcells.Intheareaclosetotheplusmargin,almostallrod-shapedcellsarepresent.Rod-shapedcellscanonlybelight-sensitive,notcolor,butthelight-sensitivesensitivityisextremelyhigh,whichis10,000timesthatofcone-shapedcells.Conecellscanbothlightandcolor.Thetwohaveacleardivisionoflabor:undertheactionofstronglight,theyaremainlyplayedbyconecells,sointhedaytimeorinabrightenvironment,thesceneseenhasbothasenseofbrightnessandasenseofcolor.Thiskindofvisioniscalledphotopic(Ordayvision).Undertheactionoflowlight,therod-shapedcellsactmainly,sointhedarkorlowlightenvironment,thescenesseenareallgrayandblack,withonlythesenseoflightanddarkness,andnosenseofcolor.
Pyramidalcellsandrod-shapedcellsareconnectedtotheopticnervethroughthebipolarmeridiancell,andtheopticnervecellleadstothebrainthroughtheopticmeridianfiber.Theopticnervegathersatapointintheretina.Thispointhasnophotosensitivecellsandiscalledablindspot.
Brightnessadaptation
Theeyescanadjustthepyramidalcellsandcolumnarcellsappropriatelytothebrightnesschangesoftheoutsideworldtomakethemhaveappropriatesensitivity.Thisphenomenoniscalled"brightnessadaptation".Theadaptationtothedarkenvironment(thebrightnessinthefieldofviewisabove0.01cd/m2,suchasdaytime,outdoors)ismainlybecausetheconecellsareinworkingcondition.Therefore,thedarkadaptationprocessisslow,whilethelightadaptationprocessismuchfaster.
Колтусна слепота
Пациентите с кокошна слепота са имали затруднения да виждат при тъмни условия поради липсата на фоточувствителни химикали (родопсин) в интеровидните клетки. Освен това в ретината на някои циркадни животни има само конусовидни клетки, но пръчковидни клетки. Циркадните животни обикновено могат да различават цветовете В ретината на животните за нощно виждане има само пръчковидни клетки и клетки с форма на конус. Животните за нощно виждане обикновено са далтонисти.
Диетична терапия
Витамин А е компонент на родопсин, който се състои от зрителни клетки, възприемащи поток от светлина.
Животните са богати на витамин А. Човешкото тяло изпитва липса на витамин А, което се отразява на способността за адаптиране към тъмнина, като деца със забавен растеж, суха кожа, сухи очи, нощна слепота и скоро.
TheminimumdailyrequirementofvitaminAfornormaladultsisabout3500internationalunits(0.3microgramvitaminAisequivalentto1internationalunit),andchildrenareabout2000to2500internationalunits.
Darkvisionbats
Foralongtime,peoplethinkthatbatsarenocturnalanimalswithdegradedeyes.Itisanindisputablefactthatbatsare"blind"becausetheymainlyuseecholocationtodeterminetheirpositionwhencapturinginsects..However,academicianZhangYapingoftheKunmingInstituteofZoology,ChineseAcademyofSciencesandhisdoctoralstudentShenYongyidiscoveredthattheoldworldfruitbatsdidnothaveecholocationcapabilities.Theymainlyreliedonvisionandsmelltofindfood,andtheireyeswere"developed".
TheresearchteamsuccessfullyclonedtheRH1genethatcontrolstheformationofrodcellsintheretina,whichdominatethescotopicreceptors.ScientistshavefoundthattherodcellsofbothinsectivorousbatswithdegradedeyesandOldWorldfruitbatswithdevelopedeyesallexpresstheRH1gene,indicatingthateventhoseinsectivorousbatswithhighlydegradedeyesstillhavedarkvision.
FurtheranalysisofthegenesequencebyZhangYaping’sresearchteamfoundthatthegenehasconvergedevolutionbetweenfruitbatsandinsectivorousbatswhoseeyeshavenotdegenerated,whilelong-wingedbatsandlong-wingedbatswithdegradedeyeshaveoccurred.Thechrysanthemumbathasalsoundergoneconvergentevolution.Thisresultrevealsthatafterthedifferentiationofbats,itispossiblethatsomespeciestendtorelymoreonvisionandhavedevelopedeyes;whileotherstendtorelylessonvisionandtheireyesdegenerate,leadingtomultipleconvergentevolutionsoftheRH1geneinbats.Thisiswhypeoplethinkthatbatshavenovision.