Cones

Visualcells

Alsoknownas"photoreceptivecells".Locatedintheretina,cellsthatconvertlightstimulationintonerveimpulses.Thevisualcelliscomposedoffourparts:outersegment,innersegment,cellbodyandendfoot.Thecellbodyisanenlargedpartcontaininganucleus,theendfootisequivalenttoanaxon,andtheinnerandouternodesareequivalenttodendrites.Theoutersegmentisthelight-sensitivepartoftheopticcell.Ithasasheet(ordisc)structurethatisfoldedandfoldedfromthecellmembrane,andcontainslight-sensitivesubstances.Theinnersegmentisslightlythicker,containsalotofmitochondria,andisthemostvigorouspartofenergymetabolism.Theoutersegmentisconnectedtotheinnersegment,and9pairsofsmallciliaextendintotheoutersegmentfromtheinnersegmenttotransmitexcitementandmaterial.Visualcellsaredividedintoconecellsandrodcells.Thereareabout6to8millionconecellsand120millionrodcellsinthehumanretina,whicharedistributedindifferentpartsoftheretina.Thereareonlyconecellsinthefoveaof​​themacula,butnorodcells.Attheedgeofthefovea,rodcellsbegintoappear,andbeyond,thenumberofrodcellsgraduallyincreases,andthenumberofconecellsgraduallydecreases.Thevisualcellscontainphotosensitivesubstances.Underlightstimulation,aseriesofphotochemicalchangesandpotentialchangescanoccur,causingthevisualcellstoemitnerveimpulses,whicharetransmittedtothebipolarcellsthroughtheendfeetofthevisualcells(conesorrods).

Conecelldystrophy

Oneofhereditarymaculardegeneration.Conecelldystrophymainlydamagestheconecells,andisalsoaccompaniedbyvaryingdegreesofrodcelldamage.Themainsymptomsarevisionloss,acquiredabnormalcolorvision,andnightblindnesscanalsooccurwhenrodcellsaredamaged.Fundusmanifestations:Thelesionsmainlyinvolvethemaculararea.Itmaybenormalatfirst.Later,thecentrallightreflectiondisappears,themacularareaisblue-graywithgoldleaf-likereflection,andtheretinalpigmentepitheliumisatrophy.Fundusfluoresceinangiography:manifestedasbullseyeordiffusedepigmentationinthemaculararea(window-likedefect).ERGshowsthatthelossofthephotopicresponseismoreseriousthanthatofthescotopicresponse.