Umbono we-20/20 ngumlinganiselo wezinto ezibonakalayo. 20/20 ubuqhetseba obubonakalayo kuthetha ukuba umntu unokubona iinkcukacha ezincinci ukusuka kwii-20 ezinyaweni ezifanayo kunye nomntu onesiqhelo esifanelekileyo uza kubona kwii-20 ezinyaweni. Ukuba umntu unobuncwane obubonakalayo obuyi-20/40, kuthiwa ubone iinkcukacha ezivela kwiinyawo ezingama-20 ezifanayo kunye nomntu onesiqhelo esifanelekileyo uza kuzibona ukusuka kwiimitha ezingama-40.
I-ophthalmologist yaseDutch, uHerman Snellen wenza i- Snellen i-acuity ebonakalayo ngo-1862. I-Snellen i-acuity ebonakalayo ibalwa njengengqengquthela kwaye imelwa njengomgama apho uvavanyo luqhutyelwa khona umgama apho i-optotype encinci iboniswe ihamba ngekota emizuzu engama-arc kunye iinkcukacha zolu hlobo lwe-optotype ludlulisa iminithi e-1 ye-arc. I-optotype yileta echanekileyo, imo, umfanekiso okanye inombolo esetyenzisiweyo ukubonisa umxholo obonakalayo ngobuninzi obubonakalayo.
Umbono we-20/20 uthathwa njengento eqhelekileyo kodwa akuthethi ukuba uthetha umbono ogqityiweyo. Ukuba nombono we-20/20 ubonisa kuphela ukucaca kombono kude. Athi nto malunga nomgangatho wemibono nezakhono zokuba nombono omuhle njengobambiswano lwezandla, ubuchule bokuhlala, ukuqonda okujulileyo, umbono we-peripheral, okanye umbono wombala. Ukongezelela, ukuba nombono we-20/20 awuthetha ukuba iliso lakho liphilile. Omnye unokufumana i- glaucoma enzima kodwa ugcine umbono we-20/20.
Kwakhona, enye ingabonwa, kodwa isilinganisi se-20/20 ebonakalayo ngaphandle kweziglasi. Abantu ababhekise phambili bakhona banokukwazi ukugxininisa kanzima kwaye bahlawule ukujonga. Nangona kunjalo, ukubambelela apho ixesha elide liyakhathaza kwaye ekugqibeleni, umbono ubonakale.
Umbono we-20/20 uthathwa njengombono oqhelekileyo.
Kungenzeka ukuba nombono ophezulu ngaphezu kwe-20/20: ubuninzi belihlo lomntu ngaphandle kwezixhobo ezibonakalayo (njengama-binoculars) ngokuqhelekileyo kucingelwa ukuba malunga ne-20/10 nangona abantu abambalwa babhalwa ukuba babe nombono we-20/5.
Ezinye iindlela zokulinganisa ubuninzi bokubonakala
"Ukudibanisa E" I-Chart Visuality Chart - Unokulinganisela njani ubuqhetseba obonakalayo kumntu ongenakuthetha okanye mhlawumbi unamahloni ukuthetha? I-Tumbling E isatifiketi isebenzisa isilinganiselo esifanayo sokulinganisa njengeStellen Eye Chart. Nangona kunjalo, zonke ii-optotypes ezisetyenzisiweyo kwitshathi ziyinkunzi E kodwa ziboniswe kwiinkalo ezahlukeneyo. Kule meko, umntu oboniswa ileta ukuba afunde kwiseshoni yamehlo angasebenzisa kuphela iminwe yakhe aze abonise ukuba uvavanyo luni na i-E ekhomba ngayo.
Uvavanyo lwe-LEA Umbono - Uvavanyo lwe-LEA luvavanyo olubonakalayo lwe-acuity eyenzelwe abantwana abangakwazi ukufunda iincwadi. Uvavanyo lusetyenziselwa ama-optotypes: i-apula, i-pentagon, isikwere kunye nesangqa. Uvavanyo lusebenzisa ezi zibonakaliso eziqhelekileyo ukwenzela ukuba ubuninzi obubonakalayo bunokulinganiswa kumncinci kakhulu.
I-Jaeger Ishici Yamehlo Ekulindeleke Kwimbono - Ukuba uhlolwe yamehlo, usenokuba ubonakaliswe ityayi yamehlo ukuze uvavanye ubunzima bakho obubonakalayo. Isatidi yeJager yincwadana encinane ephathekayo ebonisa ibhloko yeetekisi ngobukhulu obuhlukahlukeneyo.
Esikhundleni sokusebenzisa i-2/20 yekota, ityati yeJeager isebenzisa isilinganisi esukela kwiJ1 ukuya kwi-J11. I-J2 idla ngokubhekwa njengelilingana nokulinganisa kwe-20/20. Isathathi ngokuqhelekileyo sihamba phakathi kwe-12-16 intshi ukusuka kwamehlo akho.