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Sutemizuvchilarning ko'zlari humasga o'xshaydi va boshqa ko'plab hayvonlar, masalan, sakkizoyoqlarning ko'zlarida linzalar mavjud. Xo'sh, ularda bunday ko'z nuqsonlari bormi? Ha bo'lsa, ular buni qanday engishadi? Bunday hollarda ularga qarshi tanlov bosimi seziladimi?
ularda shunday ko'z nuqsonlari bormi?
Ha, ko'z nuqsoni, albatta, odamlarga xos emas. Hayvonlarda ko'z nuqsoni holatlari juda keng tarqalgan. Bu ko'pincha uy hayvonlarida kuzatiladi va biz ularni eng ko'p kuzatamiz (qarang Uy hayvonlari fiziologiyasi )
Ko'z nuqsonlari odatda daraxt sichqonlari, maymunlar (jumladan, makakalar), mushuklar, itlar, otlar, kalamushlar, fil va Cape buyvollarida kuzatilgan.
Hayvonlarda miyopiya haqidagi Vikipediya maqolasiga qarashingiz kerak
qanday qilib ular buni engishadi?
Ular aniq ko'zoynak taqishmaydi!
Odamlar ko'rish tuyg'usidan juda ko'p foydalanadilar. Ko'pgina hayvonlar hid (va ta'm), eshitish yoki teginishdan odamlarga qaraganda ko'proq foydalanadi. Bunday ko'zga ko'rinmas hayvon uchun ko'zning engil nuqsoni bo'lishi unchalik katta ish emas.
Bunday hollarda ularga qarshi tanlov bosimi seziladimi?
Bu biroz noqulay savol. Hech kim selektsiya bosimini o'ziga sezmaydi. Tanlov bosimi - bu genotiplar bilan bog'liq fitnes differentsialidir. Shuning uchun populyatsiya darajasida tanlov bosimi aniqlanadi. Bir kishiga nisbatan fitnes bosimi kabi narsa yo'q.
Keling, bu oxirgi savolni yanada mantiqiyroq narsaga aylantiraman. Men sizni qiziqtirgan savolga javob berishga amin emasman.
Ko'zi nuqsoni bo'lgan odam bo'lmagan hayvonlar ko'zlarida nuqson borligini bilishadimi?
Har qanday hayvon kognitiv qobiliyatga ega bo'lishi dargumon, ular bir xil turdagi boshqa hayvonlarga qaraganda yomonroq ko'rishlarini sezadilar. Buning uchun, hech bo'lmaganda, avtomatlashtirilgan tizimga ega bo'lishni talab qilish kerak edi va faqat bir nechta turdagi.
Boshqa hayvonlar miyopi yoki gipermetropiyadan aziyat chekadimi? - Biologiya
Sinish xatolari: ularning sabablari
Ikki bobda yuqori ilmiy darajadagi shifokorning o'ttiz yillik mehnat natijalari keltirilgan. U sinishi xatolari faqat funktsional buzilishlar ekanligini aniqlamaguncha, ular davolab bo'lmaydigan deb hisoblar edi. Uning tajribalari, bu sharoitlar mushaklarning g'ayritabiiy ta'siridan kelib chiqqanligini va shuning uchun ularning davosi faqat mushaklarni nazorat qilish masalasidir, degan shubha yo'q edi. Ushbu tajribalarning tafsilotlarini 1915 yil 8-maydagi Nyu-York tibbiyot jurnalida topish mumkin.
E Sinishining RRORSlari ko'rishning buzilishi holatlarining aksariyati uchun javobgardir va ko'pincha ko'zning haqiqiy kasalligiga olib keladi. Bu xatolar to'rt sinfga bo'linadi: miyopi, gipermetropiya, astigmatizm va presbiyopiya.
Qisqa ko'rish yoki yaqin ko'rish deb ataladigan miyopiyada uzoqdan keladigan yorug'lik nurlari to'r pardasi oldiga qaratiladi.
Gipermetropiyada ular retinaning orqasida joylashgan. Bu holat odatda uzoqni ko'rish yoki uzoqni ko'rish deb ataladi, lekin aslida ko'rish ham yaqin, ham uzoqni ko'rish uchun noto'g'ri.
Astigmatizmda nurlar bitta fokusga qaratilmaydi, chunki refraktsion sirtlarning egriligi ma'lum meridianlar bo'ylab boshqalarga qaraganda kattaroqdir. Astigmatizmning olti xil turi mavjud.
Agar bitta meridian to'g'ri va unga to'g'ri burchakli bo'lsa, u miyopik yoki gipermetropik bo'lsa, bu holat oddiy miyopik yoki gipermetropik astigmatizm deb ataladi, agar ikkala meridian ham gipermetropik yoki miyopik bo'lsa, lekin boshqasidan farqli o'laroq, biz murakkab gipermetropik yoki miyopik astigmatizmga ega bo'lamiz. miyopi va gipermetropiyaning kombinatsiyasi aralash astigmatizm deb ataladi. Astigmatizmsiz oddiy gipermetropiya yoki miyopiya kamdan -kam uchraydi.
Presbiopiya - bu odatda qirqdan ellikgacha bo'lgan ko'zning holati va odamni o'qish yoki tikish uchun ko'zoynak taqishga majbur qiladi, uzoqdan ko'rish, birinchi navbatda, sezilmaydi.
Yuqorida ta'kidlab o'tilganidek, bu sharoitlar odatda davolab bo'lmaydigan va ko'p jihatdan muqarrar bo'lishi kerak, ammo ular faqat funktsional muammolar ekanligini va shuning uchun ham davolash mumkin, ham oldini olish mumkinligini ko'rsatadigan ko'plab dalillar mavjud.
Quyon va siliyer mushaklarning turar joy bilan hech qanday aloqasi yo'qligini, aksincha, butun shakli shakli, klinik va quyonlar, baliqlar va boshqa hayvonlarning ko'zlarida o'tkazilgan tajribalar orqali ham ko'rsatilishi mumkin va ko'rsatildi. tashqi ko'z mushaklari orqali, ko'z fokusi o'zgartirilganda o'zgaradi. Ob'ektivni eksperimental hayvonlarning ko'zidan olib tashlash yoki ko'rish chizig'idan chiqarib yuborish (24 -bet, III bob) kabi, ular avvalgidek joylashishni davom ettirdilar. Ba'zi muskullar, ya'ni qiya mushaklari buzilmagan ekan, ko'z olmasining yoki akkomodatsiya nervlarining elektr stimulyatsiyasi doimo akkomodatsiyani hosil qilgan, ammo ulardan biri kesilganda akkomodatsiya ishlab chiqilmagan. Kesilgan mushak yana tikilganida, turar joy avvalgidek bo'lib o'tdi.
Bu kuzatishlar ob'ektivsiz odam ko'zlarida joylashish yozuvlari bilan mos keladi, ular yuz yildan ko'proq vaqt davomida adabiyotda tarqalgan. Afsuski, ko'p odamlar katarakt operatsiyasida linzalarini yo'qotadilar va odatda ularga keyinchalik ikkita ko'zoynak, biri o'qish uchun, ikkinchisi masofa uchun beriladi, lekin vaqti -vaqti bilan bunday odam har ikki masofada ham o'zgarmasdan ko'radi. ko'zoynaklar. Bu kuzatuvlarning to'g'riligi ilgari bahs -munozara qilinar edi, lekin endi buni amalga oshirish mumkin emas, shuning uchun linzalar turar joyning yagona agenti bo'la olmaydi degan fikr pravoslav adabiyotiga kirib bormoqda.
Ushbu faktlardan ko'rinib turibdiki, ko'pchilik tsivilizatsiya sharoitida yashovchi ko'pchilikning keyingi yillarida paydo bo'ladigan ko'rishning buzilishining sababi nima bo'lishidan qat'i nazar, bu ob'ektivning qattiqlashishi bo'lishi mumkin emas, chunki ko'zdagi fokusning o'zgarishi unga bog'liq. tashqi muskullar ta'sirida, biz tabiiy ravishda diqqatni to'g'ri to'lamaslik bu mushaklarning ishlamay qolishi bilan bog'liq bo'lishini kutamiz. Bu xulosaning to'g'riligini hayvonlarning ko'z mushaklarida o'tkazilgan ko'plab tajribalar ko'rsatdi.
Bu mushaklar ko'z olmasining atrofida deyarli to'liq tasma hosil qiladi va ular qisqarganda uni uzaytiradi, chunki kamera yaqin nuqtada suratga olish uchun uzaytiriladi.
Ushbu tajribalarda miyopi oblikalarning tortilishini kuchaytiruvchi operatsiyalar natijasida hosil bo'ldi, bu esa ko'zning gipermetropiyasini cho'zilishiga olib keldi, bu to'g'ri ichak deb nomlanuvchi mushaklar majmuasini tortish kuchini oshirdi, shu bilan ko'z nuri va astigmatizmini nosimmetrik o'zgarishiga olib keldi. ko'z olmasining shakli (25 -betdagi kabi, III bob). Bir yoki bir nechta obliklarni kesish, bundan tashqari, miyopi paydo bo'lishining oldini oldi, gipermetropiya esa bir yoki bir nechta to'g'ri chiziqni kesish orqali oldini oldi.
Bu kuzatuvlar, hech qanday ko'zda sinish xatosi mavjud bo'lganda, tashqi mushaklar uni shaklini qisib qo'ygani, yoki hozircha juda uzun yoki juda qisqa qilib qo'ygani yoki uzaytirgani yoki notekis qisqartirganiga shubha qilishga o'rin qoldirmaydi. . Ko'rinib turibdiki, miyopi egilgan mushaklarning g'ayritabiiy qisqarishi, to'g'ri ichakning g'ayritabiiy qisqarishi gipermetropiyasi va bu ikki mushaklar majmuasining teng bo'lmagan qisqarishi astigmatizmidan kelib chiqadi, bu esa bir qismining boshqa qismiga qaraganda ko'proq cho'zilishi yoki qisqarishiga olib keladi. Presbiyopiyada, to'g'ri ichakning g'ayritabiiy harakati, birinchi navbatda, ob'ekt uzoqdan ko'rinishni qoldirgan holda, yaqin narsalarga qaraydigan, ammo biroz ta'sirlangan, ammo keyinchalik uzoqdan ko'rish ham muvaffaqiyatsizlikka uchragan davrlar bilan chegaralanadi.
Bu shartlar ko'zning shakli o'zgarishi bilan bog'liq bo'lishi mumkin emasligi, ularni retinoskop ko'rsatganidek, bir lahzada o'z xohishiga ko'ra ishlab chiqarilishi va minglab kasalliklardan davolanganligi bilan yana bir bor isbotlanadi. holatlar, ular tez -tez davolanmasdan yo'qoladi.
Mushaklarning bunday g'ayritabiiy harakatining sababi - ko'rish, ko'rishning ongli yoki hushidan ketishi, shuning uchun ham oldini olish mumkin, ham davolash mumkin.
Ushbu zo'ravonlikning asosiy sabablari, shubhasiz, ibtidoiy yovvoyi hayotdan ultratsivilizatsiyaga o'tishni belgilab bergan omillardir. Noto'g'ri ovqatlanish odatlari, yomon havo va sayoz nafas olish, kam harakat qilish, cho'milish va quyosh nuri, ich qotishi, stimulyatorlarning haddan tashqari ko'p ishlatilishi, shahar shovqinlari, shoshilish, xavotirlanish, raqobat va umuman jismoniy va ruhiy zo'ravonlik madaniyatli hayot bilan bog'liq. butun tananing, shu jumladan ko'zlarning zo'riqishi va zo'riqishi. Eshitish va boshqa hislar ko'rish kabi azob chekadi.
NDA & NA (II) 2017 imtihon: GK Amaliy savollari &ndash Umumiy fanlar toʻplami 01
NDA II imtihoni 2017 aspirantlari manfaati uchun Jagran Josh General Sceince bo'yicha amaliy savollarni taqdim etadi. O'tilgan mavzular &ndash Kasalliklar, Ovqat hazm qilish tizimi, Odam anatomiyasi va boshqalar.
UPSC 2017 yil 10 sentyabrda NDA & amp NA (II) 2017 imtihonini o'tkazadi. Imtihon ikkita hujjatdan - matematika va umumiy qobiliyat testidan iborat bo'ladi. Javoblar va tushuntirishlar bilan quyida berilgan 10 ta savol nomzodlarga umumiy qobiliyat testining GK bo'limidagi ballarini yaxshilashda yordam beradi.
1. Bezgak paraziti a
Javoblar (b) protozoa
Bezgak - bu odamlar va boshqa hayvonlarga ta'sir qiladigan chivinlar orqali yuqadigan yuqumli kasallik. Kasallik Plasmodium turiga mansub parazit protozoanlar tomonidan chaqiriladi. Protozoa bir hujayrali mikroorganizmlar guruhidir. Protozoa keltirib chiqaradigan boshqa kasalliklar: amoebik dizenteriya, uyqu kasalligi va Kala azar.
2. Viruslarni o'ldirish qiyin, chunki ular
(a) qattiq oqsil qoplamidan iborat
(b) hajmi juda kichik
(c) hujayra tuzilishi yo'qligi
(d) uy egasining hujayralarida ko'p vaqt o'tkazish
Javoblar (d) ko'p vaqtni uy egasi hujayralarida o'tkazadi
Virus tanamizga kirganda, u hujayraga hujum qilishga urinadi. Agar bizning immunitetimiz virusni bosqinchi sifatida tan olsa, virus hujayraga kirishidan oldin u yo'q qilinadi. Aks holda, infektsiya jarayoni boshlanadi. Hujayra ichiga kirgandan so'ng, virus hujayraning o'ziga xos replikatsiya mexanizmini o'g'irlab ketishi mumkin, u virusning ko'p nusxalarini yaratishni boshlaydi. Ushbu viruslar hujayradan chiqib, uni yo'q qiladi va immunitet tizimi tomonidan bartaraf etilmasa, yana ko'plab hujayralarni yuqtirishga harakat qiladi.
3. Inson ko'zoynaksiz gazeta o'qiy olmaydi. U, ehtimol, azob chekadi
Javoblar (b) presbiyopiya
Presbiyopiya - bu ko'zning qarishi bilan bog'liq bo'lgan holat bo'lib, yaqin ob'ektlarga aniq e'tibor qaratish qobiliyatining tobora yomonlashishiga olib keladi. Semptomlar orasida kichik harflarni o'qish qiyinligi, o'qish materialini uzoqroq tutish, bosh og'rig'i va ko'z charchoqlari kiradi. Turli xil odamlar turli darajadagi muammolarga duch kelishadi. Boshqa turdagi refraktsion xatolar presbiopiya bilan bir vaqtda bo'lishi mumkin.
4. Bakteriyalarning genetik materiali
v) hujayra membranasi
Javoblar (b) sitoplazma
Bakteriyalar - bu prokaryotlar. Shuning uchun ular yaxshi aniqlangan yadroga ega emaslar. Ularning genetik materiali dumaloq va ikki torli DNKdan iborat bo'lib, sitoplazmada erkin suzadi va membrana bilan bog'lanmagan. Sitoplazmadagi genetik material suzuvchi hudud nukleoid deb nomlanadi.
5. Ot va eshak tug‘maydigan hayvon bo‘lgan xachirni ko‘paytirishi mumkin. Bepushtlikning sababi shundaki, ot va eshak boshqalarga tegishli
Javoblar (c) turlari
Biologiyada tur biologik tasnifning asosiy birligi va taksonomik daraja hisoblanadi. Turlar odatda jinsiy ko'payish yo'li bilan ikki shaxs unumdor nasl berishlari mumkin bo'lgan eng katta organizmlar guruhi sifatida aniqlanadi.
6. O'lik dog'lar bilan sariq barglari bo'lgan o'simlikda etishmovchilik mavjud
Javoblar (b) magniy
Etarli miqdorda magniy bo'lmasa, o'simliklar eski barglardagi xlorofillni yo'q qila boshlaydi. Bu magniy etishmasligining asosiy belgisiga, barglar marmar ko'rinishga ega bo'lib, yashil rangda qoladigan xloroz yoki barg tomirlari o'rtasida sarg'ayishiga olib keladi. Keksa barglar qirg'oqda sarg'ayadi, interveinal xloroz o'qning uchida yashil shakl yoki ebruga olib keladi (donli dog'lar).
7. Ftorli tish pastasi ba'zida tavsiya etiladi, chunki ftorid
(a) blyashka shakllanishiga to'sqinlik qiladi
(b) tishning emalini qattiqlashtiradi
v) patogen bakteriyalarni o'ldiradi
(d) tish og'rig'ini oldini oladi
Javoblar (b) tishning emalini qattiqlashtiradi
Emalning yo'qolishi remineralizatsiya bilan muvozanatlanadi. Remineralizatsiya paytida ftor mavjud bo'lganda, tish emaliga tushgan minerallar tishlaringizni mustahkamlashga yordam beradi va keyingi demineralizatsiya bosqichida erishini oldini oladi. Shunday qilib, ftor parchalanish jarayonini to'xtatishga va tishlarning parchalanishini oldini olishga yordam beradi.
8. Quyidagi gaplardan qaysi biri to'g'ri?
a) Prokaryotik hujayralar yadroga ega.
b) Hujayra membranasi o'simlik va hayvon hujayralarida bo'ladi.
v) Mitoxondriya va xloroplastlar eukaryotik hujayralarda uchramaydi.
d) Ribosomalar faqat eukaryotik hujayralarda bo'ladi.
Javoblar b) Hujayra membranasi o'simlik va hayvon hujayralarida bo'ladi.
Eukaryotik hujayralar DNKni o'z ichiga olgan "haqiqiy" yadroga ega bo'lsa, prokaryotik hujayralarda esa yadro yo'q. Eukaryotik hujayralarda mitoxondriya va xloroplastlar uchraydi. Eukariotlar ham, prokaryotlar ham protein ishlab chiqaradigan ribosomalar deb ataladigan katta RNK/oqsil tuzilmalarini o'z ichiga oladi.
9. Quyidagi gaplardan qaysi biri sutemizuvchilarga to'g'ri kelmaydi?
a) Ularning tanasida sochlari bor.
b) Ulardan ba'zilari tuxum qo'yadi.
v) Ularning yuragi uch kamerali.
d) ba'zilari suvda yashaydi.
Javoblar v) Ularning yuragi uch kamerali
Sutemizuvchilar va qushlarning yuragida to'rtta kamera, ikkita atrium va ikkita qorincha bor. Bu eng samarali tizimdir, chunki kislorodsiz va kislorodli qonlar aralashmaydi. O'ng atrium tanadan kislorodsiz qonni pastki va yuqori vena kava orqali oladi.
10. Odamning ovqat hazm qilish tizimida ovqat hazm qilish jarayoni boshlanadi
(b) bukkal bo'shliq
(c) o'n ikki barmoqli ichak
Javoblar (b) bukkal bo'shliq.
Ovqat hazm qilish jarayoni bukkal bo'shliqda boshlanadi. U og'iz yoki og'iz bo'shlig'i deb ham ataladi. Inson anatomiyasida og'iz ovqatni qabul qiladigan ovqat hazm qilish kanalining birinchi qismidir.
Miyopi (uzoqni ko'ra olmaslik yoki uzoqni ko'ra olmaslik)
Miyopi (yoki uzoqni ko'ra olmaslik)-bu ko'rish nuqsoni, odam uzoqdagi narsalarni aniq ko'ra olmaydi (garchi u yaqin atrofdagi narsalarni aniq ko'rsa ham). Miyopi bilan og'rigan ko'zning uzoq nuqtasi cheksizlikdan kam. Bunday odam faqat bir necha metr (yoki undan ham kamroq) masofani aniq ko'ra oladi.
Miyopi (yoki uzoqni ko'ra olmaslik) deb ataladigan ko'z nuqsoni paydo bo'ladi
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Miyopi genetikasini o'rganishda ilmiy yutuq
Olimlarning fikriga ko'ra, ular nima uchun ko'p vaqtini tashqarida o'ynashdan ko'ra, uyda o'tkazadigan, miyopi genetikasini o'rganganidan so'ng, uzoqni ko'ra olmaslik ehtimoli ko'proq ekanligini bilib olishlari mumkin.
Yigirma dan ortiq genlar miyopi rivojlanish xavfining oshishi bilan bog'liq bo'lib, natijada tadqiqotchilar bugungi bolalar nima uchun o'tmishdagi bolalarga qaraganda uzoqni ko'ra olmasliklari mumkinligini tushunishga imkon berishi mumkin.
Miyopi hozirda G'arbda har uchinchi odamda va Osiyoda 80 foizgacha odamda uchraydi. Uzoq Sharqdagi ba'zi mamlakatlarda bolalarning 90 foizigacha ko'rish qobiliyati cheklangan, bundan bir necha o'n yillar oldin 20 foizdan kam.
Olimlarning fikricha, uzoqni ko'ra olmaslik oilalarda tez-tez uchrab turadi va irsiy tarkibiy qismga ega bo'lsa-da, so'nggi yillardagi holatning keskin o'sishi bolalarning uyda o'qish, kompyuter o'yinlari va televizor ko'rish vaqtining ko'payishi bilan bog'liq. .
Evropa va Osiyodan 45000 dan ortiq odamlarni o'rganish natijasida miyopi boshlanishini qo'zg'atadigan 24 yangi gen aniqlandi. Olimlarning ta'kidlashicha, u uzoqni ko'ra olmaslik bilan bog'liq deb gumon qilingan yana ikkita genning rolini tasdiqladi.
"Biz miyopiya yoki uzoqni ko'ra olmaslik oilalarda paydo bo'lishini allaqachon bilar edik, ammo shu paytgacha biz genetik sabab haqida kam bilar edik. Bu tadqiqot birinchi marta miyopi bilan bog'liq bo'lgan yangi genlar guruhini ochib beradi ”, - deydi London King's College kolleji professori Kris Hammond, tabiat genetikasida chop etilgan tadqiqotga rahbarlik qilgan.
"Bu genlarning ba'zilarining tashuvchilarida kasallikning rivojlanish xavfi o'n barobar oshadi ... Bu kelajakda butun dunyo bo'ylab millionlab odamlarni davolash yoki oldini olishga yordam beradigan o'ta hayajonli qadamdir", dedi u.
Miyopi, ko'z olmasi juda uzun o'sganda, ko'zning orqa qismidagi nurga sezgir to'r pardasiga qisqa fokuslanishiga olib keladi. Professor Hammondning aytishicha, bolalik davridagi yorug'lik darajasi ko'zning o'sishini boshqaradi, kam yorug'lik esa miyopiyaga olib keladi.
Yoshligida miyopi rivojlangan bolalar, uzoqni ko'ra olmaydigan bolalarga qaraganda, keyingi hayotda ko'rish muammolariga ko'proq duch keladilar. Haddan tashqari holatda, miyopi o'rta yoshdan keyin ko'rishning jiddiy muammolariga olib kelishi mumkin, masalan, glaukoma, ajratilgan to'r pardasi va makula nasli tufayli ko'rlik.
“Ko'rish qobiliyatini yo'qotish xavfi katta bo'lgan o'rta yoshda jiddiy muammolar mavjud. Buning asosiy sababi, ko'z olmasining uzunroq bo'lishi va to'r pardaning kengroq joyga cho'zilganligidadir, - dedi professor Hammond.
Miyopiyada har biri kichik, ammo muhim rol o'ynaydigan 26 ta genning topilishi ko'z olmasining haddan tashqari o'sishiga olib kelishi mumkin bo'lgan biokimyoviy yo'llar va uning oldini olish usullarini tushunishga yo'l ochadi, dedi u.
"Hozirgi vaqtda miyopi rivojlanishini kamaytirish imkoniyatlari juda cheklangan. Atropin deb ataladigan bitta dori uning rivojlanishini kamaytirishi mumkin bo'lsa -da, u o'quvchini kengaytiradi va yorug'lik sezuvchanligi va o'qish qiyinligi bilan bog'liq muammolarni keltirib chiqaradi ", - deydi professor Hammond.
“Biz nihoyat qisqa ko‘rishga olib keladigan mexanizmni tushunishga harakat qilmoqdamiz, bu biz boshqa hayvonlarda ko‘rmaydigan narsadir. Ko'z to'pi o'sishda davom etishiga to'sqinlik qiluvchi "to'xtash signali" juda kuchli va biz uning qanday ishlashini bilishni bilamiz ", dedi u.
Atrof-muhitning genlar bilan o'zaro ta'siri miyopi rivojlanish xavfini aniqlashda muhim ahamiyatga ega, bu ta'lim, urbanizatsiya va tashqi faoliyat bilan bog'liq, dedi professor Hammond.
“Buyuk Britaniyada bolalarda uzoqni ko‘ra olmaslik tez-tez uchrab borayotganini ko‘rsatadigan ba’zi ma’lumotlar mavjud. Ehtimol, kompyuter o'yinlarida yopiq o'tirish, ochiq havoda ko'kka qaragandek yaxshi emas ", dedi u.
Giperopiya va miyopi o'rtasidagi farq
Bu ikkita muammo bo'yicha yuqoridagilardan tashqari, bir -biridan farqini ko'rsatadigan boshqa tafsilotlar ham bor. Agar sizda bu haqda shubhangiz bo'lsa yoki shunchaki bilganingizni to'ldirish uchun ma'lumot qidirsangiz, o'qishni davom eting, chunki quyida biz sizga miyopi va uzoqni ko'ra olmaslik o'rtasidagi farqni tushuntiramiz.
Nomidan ko'rinib turibdiki, miyopi yoki qisqa ko'rish - bu juda yaqin bo'lmagan narsalarni ko'rishning qiyinligi bilan tavsiflanadigan holat, ya'ni odamdan ma'lum masofada joylashgan narsa xiralashgan holda ko'rinadi. odam.
Bu muammo shundaki, shox parda shunchalik cho'zilganki, u kiruvchi nurni to'g'ridan-to'g'ri retinaga qaratishga to'sqinlik qiladi. Bu, shuningdek, irsiy kasallik bo'lib, agar ota -onalardan birida yoki ikkalasida ham bunday kasallik bo'lsa, azoblanish ehtimoli oshadi.
Irsiy xususiyatga qaramay, miyopi rivojlanishida ba'zi atrof-muhit omillari ham muhim rol o'ynashi mumkin. Masalan, siz hali ham kichkinaligingizda juda ko'p vaqtni yopib qo'yishingiz, quyosh nuri bilan etarlicha aloqa qilmasligingiz va diqqat bilan qarashingizni talab qiladigan vazifalarni bajarishga ko'p vaqt sarflashingiz. Shunga o'xshab, bu holatning rivojlanishiga jinsi, irqi, yoshi va hatto biologik soat kabi omillar ta'sir ko'rsatishi mumkin. Garchi bu ma'noda hamma narsa spekulyativ ekanligini tushuntirish yaxshi bo'lsa -da, o'zaro bog'liqlikni o'rnatish uchun etarli ma'lumot yo'q. aniq sababni aniqlash uchun kamroq.
Giperopiya yoki giperopiya
Boshqa tomondan, giperopiya - bu miyopiyaga qarama -qarshi deyish mumkin bo'lgan holat. Taqdimotchiga yaqin atrofdagi narsalarni ko'rish qiyin, chunki ular loyqa ko'rinadi, ammo siz uzoqda bo'lganlarni juda yaxshi ko'rishingiz mumkin. Buning sababi shundaki, ko'z qobig'i juda kichkina bo'lib, kiruvchi yorug'lik to'r pardasi orqasida fokuslanadi.
Nihoyat, gipermetropiyaning asosiy sababini ko'p sabablari bor, chunki tug'ilishdan boshlab odamda ko'zning kichkina ko'zlari bor. Ba'zi hollarda, bolaning o'sishi va balonning uzayishi bilan bu holat o'zini o'zi tuzatadi. Shuningdek, diabet va retinada qon tomirlari bilan bog'liq muammolar gipermetropiyaga olib kelishi mumkin. Ikkala holatda ham eng keng tarqalgan davolash ko'zoynaklardan foydalanish hisoblanadi.
3 -bob – Nurning prizma orqali sinishi
Quyidagi mavzular va kichik mavzular ushbu bobda yoritilgan va MSVgo-da mavjud:
Fizika darsida siz uchlari bir xil va yuzi uchburchak shaklidagi qattiq shisha buyumni uchratgan bo'lishingiz mumkin. Uzunligi bo'yicha bir xil kesimga ega bo'lgan bu ob'ekt prizma deb nomlanadi. Shakl va o'lchamdagi boshqa variantlar ham bor, lekin bu prizmaning eng keng tarqalgan tuzilmalaridan biridir. A prism is used to break white light into multiple constituent spectral colors, that is, the seven colors of rainbows. Prisms are also used for refracting light and splitting it into multiple components with different polarization processes.
Refraction of Light Through a Prism
Refraction is the process of bending light when it passes from one medium to another. In a similar context, when light passes through a prism, it travels from air to a solid glass object, which causes the light ray to deviate, change its direction, and get divided into different colors.
Power of Accommodation
The ability of the human eye to adjust to see objects from both near and far is called the power of turar joy . The process of accommodation tends to involve the lens of the eye and ciliary muscles. The work of ciliary muscles is to modify the curvature of the lens, due to which the focal length of the lens is affected. In other words, accommodation is the process by which the vertebrate eyes tend to change the eyes’ optical power. This helps them to maintain a clear focus on the image irrespective of the distance between a rigid lens and the muscles of the retina.
An advanced sunrise and a delayed sunset are the two primary examples of atmospheric refraction that humans can notice in their daily life. These phenomena are caused by the random flickering of the hot air and turbulent streams in the earth’s atmosphere. Atmospheric refraction is the process of light deviating from its straight-line path as it passes through different types of atmosphere with varied air density resulting from changes in height. Atmospheric refraction can therefore be defined as the deviation of light or any other sort of electromagnetic wave from a straight line followed. This happens when light passes through a different environment with a variation in air density, which causes it to change its height.
Scattering of Light
Scattering of light occurs when light particles pass through some imperfect medium filled with other particles, due to which light is deflected from its straight path. With this phenomenon, light scatters in multiple directions. One of the best examples of scattering of light is the deflection of sun rays when they pass through clouds. Scattering of light is also known as ‘Rayleigh scattering’ after Lord Rayleigh. He proved that scattering of light occurs elastically and dominates electromagnetic waves, which pass through imperfect mediums with different particles. Rayleigh also claimed that light is deflected in areas with particles due to the small wavelength of the area. The Tyndall Effect is one of the key examples of scattering of light. The Tyndall Effect can be described as light scattering by particles through the method of colloid or very fine suspension.
Science Question World
Javoblar The pupil of an eye acts like a variable aperture whose size can be varied with the help of the iris and the adjustment of the pupil takes time. So, when we enter from bright sunlight to a dark room, we cannot see initially.
3. A person uses spectacles of power +2D. What is the defect of vision he is suffering from?
Javoblar A person who uses spectacles of power +2D means he is suffering from hypermetropia (long-sightedness).
4. Why do chickens wake up early and sleep early?
Javoblar Chickens have a large number of rod cells that help them to detect the intensity of light. Thus, chickens wake up early and go to sleep early .
5. What is the nature of the image formed at retina?
Javoblar T he image formed at the retina is diminished, inverted and real.
6. What is the cause of colour blindness?
Javoblar C one cells of the retina are sensitive to colours and when these cells do not respond properly , enable the retina to distinguish between colors.
7. State the structure of iris and its functions in the human eye.
Javoblar. A structure called iris behind the cornea is a dark muscular diaphragm that controls the size of the pupil and the pupil regulates and controls the amount of light.
8. Define the distance of distinct vision and give its range.
Javoblar The minimum distance, at which objects can be seen most distinctly without strain, is called the least distance of distinct vision and its range is about 25 cm .
9. What is meant by the least distance of distinct vision?
Javoblar T he least distance of distinct vision means the minimum distance, at which objects can be seen most distinctly without strain.
10. Define the power of accommodation of the eye.
Javoblar The ability of the eye lens to adjust its focal length is called the power of accommodation.
11. Why the clear sky appear blue?
Javoblar When sunlight passes through the atmosphere the fine particles in the air scatter the blue colour, so the clear sky appears blue.
12. Why does it take some time to see objects in a cinema hall when we just entered the hall from bright sunlight? Explain in brief.
Javoblar The pupil of an eye acts like a variable aperture whose size can be varied with the help of the iris and the adjustment of the pupil takes time. So, it takes some time to see objects in a cinema hall when we just entered the hall from bright sunlight.
13. How does the thickness of the eye lens change when we shift looking from a distance tree to reading a book?
Javoblar The thickness of the eye lens increases when we shift looking from a distance tree to reading a book.
14. A student sitting at the back of the classroom cannot read clearly the letters written on the blackboard. W hat advice will a doctor give to her?
Javoblar The student is a short-sightedness or Myopia and a doctor will give her advice to take a spectacle of -ve power means the concave lens of suitable power.
15. A hyper meteoric person prefers to remove his spectacles while driving. Give reason.
Javoblar A person with hypermetropia can see distant objects clearly and during driving a person has to see more than a nearer point (25 cm). Buning sababi
a hyper meteoric person prefers to remove his spectacles while driving.
16. How are we able to see nearby and also the distant objects clearly?
Javoblar W e are able to see nearby and also the distant objects clearly by the ability of the eye lens to adjust its focal length that is called power accommodation.
17. Why do parallel rays of different colours deviate differently while passing through a glass prism?
Javoblar Different colours of light bend through different angles with respect to the incident ray while passing through a prism as they have different wavelengths.
18. Name any two phenomena associated with the formation of the rainbow.
Javoblar. T wo phenomena associated with the formation of the rainbow are internal reflection and dispersion.
19. Draw a ray diagram showing the dispersion through a Prism when a narrow beam of white light is incident on one of its refracting surfaces. Also, indicate the order of the colours of the spectrum obtained.
20. Define the angle of deviation.
Javoblar The angle between the incident ray and emergent ray is called the angle of deviation.
21. List the colours into which light splits in the decreasing order of their bending on emergence from the prism.
Javoblar. Red, orange, yellow, green, blue, indigo and violet.
22. A beam of white light splits when it passes through a Prism. Name this phenomenon and give its reason.
Javoblar The phenomenon is refraction and the reason is the different wavelengths of a different colour and different colour deviate from different angles.
23. Why does the sun look reddish at the time of sunrise and sunset? Tushuntiring.
Javoblar During sunrise and sunset , l ight from the Sun near the horizon passes through thicker layers of air and larger distance in the earth’s atmosphere. Shorter wavelengths are scattered away by the particles and most of the red light of a longer wavelength which is least scattered reaches our eyes. This gives rise to the reddish appearance of the Sun.
24. Why do different components of white light split up into a spectrum, when it passes through a triangular glass prism?
Javoblar Different colours of light bend through different angles with respect to the incident ray while passing through a prism as different colours have different wavelengths so deviate from different angles.
25. What is the dispersion?
Javoblar The splitting of light into its seven component colours is called dispersion.
26. What happens when light is passed through a glass prism.
Javoblar Different colours of light bend through different angles with respect to the incident ray, as they pass through a prism.
27. What is astigmatism?
Javoblar Astigmatism is a common vision problem caused by irregular-shaped of cornea, that causes blurred vision.
28. Name the defect of vision in which the eye loses its power of accommodation due to old age.
II. Short answer type questions:
(b) State two reasons due to which the myopia eye defect may be caused?
(b) This defect may arise due to
(i) excessive curvature of the eye lens, or
(ii) elongation of the eyeball.
Javoblar No, the position of a star as seen by us is not it's true position. The atmospheric refraction occurs in a medium of gradually changing the refractive index. Since the atmosphere bends starlight towards the normal, the apparent position of the star is slightly different from its actual position. The star appears slightly higher than its actual position when viewed near the horizon.
16. What will be the colour of the sky be for an astronaut staying in the International Space Station orbiting the earth? Justify your answer by giving reasons.
Javoblar T he colour of the sky will be black for an astronaut staying in the International Space Station orbiting the earth because there is no atmosphere in the space and the light reaching it does not scatter. Scattering of blue light of short wavelength causes the blue colour of the sky.
Javoblar The angle between the incident ray and emergent ray is called the angle of deviation.
Different components of white light split up into spectrum when it passes through a triangular glass prism because different colour has a different wavelength and deviate with different angles.
24. Why the power of accommodation of an eye decreases with age? Tushuntiring.
Javoblar The power of accommodation of the eye usually decreases with ageing. I t arises due to the gradual weakening of the ciliary muscles and diminishing flexibility of the eye lens.
25. Draw ray diagram each show:
(i) Myopic eye (ii) Hypermetropic eye.
Javoblar. (i) Myopic eye-
III. Long answer type questions:
1. A student suffering from myopia is not able to see distinctly the objects placed beyond 5 m. List two possible reasons due to which this defect of vision may have arisen. With the help of ray diagrams, explain.
Javoblar Myopia is known as short-sightedness. A myopic person can see nearby objects clearly but cannot see distant objects distinctly. In a myopic eye, the image of a distant object is formed in front of the retina and not at the retina itself.
This defect may arise due to
(i) excessive curvature of the eye lens, or (ii) elongation of the eyeball.
This defect can be corrected by using a concave lens of suitable power. A concave lens of suitable power will bring the image back on to the retina and thus the defect is corrected.
2. (i) Why the student is unable to see distinctly the objects placed beyond 5m from his eyes.
(ii) the type of corrective lens used to restore proper vision and how this defect is corrected by the use of this lens.
Javoblar See the answer of Q.1
3. List the parts of the human eye that control the amount of light entering into it. Explain how they perform this function.
Javoblar Iris and pupil are the two parts of the eye that controls the amount of light entering into it. Iris behind the cornea is a dark muscular diaphragm that controls the size of the pupil. The pupil regulates and controls the amount of light entering the eye.
The pupil of an eye acts like a variable aperture whose size can be varied with the help of the iris. When the light is very bright, the iris contracts the pupil to allow less light to enter the eye. However, in dim light, the iris expands the pupil to allow more light to enter the eye. Thus, the pupil opens completely through the relaxation of the iris.
4. Write the function of the retina in the human eye. Do you know that corneal impairment can be cured by replacing the defective cornea with the cornea of a donated eye? How and why should we organise groups to motivate the community members to donate their eyes after death?
Javoblar The retina of human eye act as a screen. The eye lens forms an inverted real image of the object on the retina. The retina is a delicate membrane with having an enormous number of light-sensitive cells. The light-sensitive cells get activated upon illumination and generate electrical signals. These signals are sent to the brain via the optic nerves. The brain interprets these signals, and finally, processes the information so that we perceive objects as they are.
By donating our eyes after we die, we can light the life of a blind person.
About 35 million people in the developing world are blind and most of them can be cured. About 4.5 million people with corneal blindness can be cured through corneal transplantation of donated eyes. One pair of eyes gives vision to TWO CORNEAL BLIND PEOPLE.
5. List three common refractive defects of vision. Suggest the way of correcting these defects.
Javoblar Three common refractive defects of vision are myopia or short-sightedness, hypermetropia or long-sightedness and presbyopia.
Myopia - A person with myopia can see nearby objects clearly but cannot see distant objects distinctly. In a myopic eye, the image of a distant object is formed in front of the retina. This defect can be corrected by using a concave lens of suitable power. A concave lens of suitable power will bring the image back on to the retina and thus the defect is corrected.
Hypermetropia - Hypermetropia is also known as far-sightedness. A person with hypermetropia can see distant object clearly but cannot see nearby objects distinctly. This is because the light rays from a close-by object are focussed at a point behind the retina.
This defect can be corrected by using a convex lens of appropriate power. Eye-glasses with converging lenses provide the additional focusing power required for forming the image on the retina.
Presbyopia- The power of accommodation of the eye usually decreases with ageing. They find it difficult to see nearby objects comfortably and distinctly without corrective eye-glasses. This defect is called Presbyopia. It arises due to the gradual weakening of the ciliary muscles and diminishing flexibility of the eye lens. Such people require A common type of bi-focal lenses consists of both concave and convex lenses. These days, it is possible to correct the refractive defects with contact lenses or through surgical interventions.
6. About 45 lakh people in the developing countries are suffering from corneal blindness about 3 lakh children below the age of 12 suffering from this defect can be cured by replacing the defective, with the cornea of a donated eye. How and why can a student of your age involve themselves to create awareness about this fact among people?
Javoblar Try to yourself.
7. A person cannot read a newspaper place near 50 cm from his eye. Name the defect of vision he is suffering from? Draw a ray diagram to illustrate the defects. List two possible causes. Draw a ray diagram to show how this defect may be corrected using a lens of appropriate focal length. We see an advertisement for eye donation on television or a newspaper. Write the importance of such advertisement.
Javoblar. A person cannot read a newspaper place near 50 cm from his eye. The person is hypermetropic. He can see distant objects clearly but cannot see nearby objects distinctly. This is because the light rays from a close-by object are focussed at a point behind the retina . This defect arises either because
(i) the focal length of the eye lens is too long, or
(ii) the eyeball has become too small.
This defect can be corrected by using a convex lens of appropriate power. Eye-glasses with converging lenses provide the additional focusing power required for forming the image on the retina.
Advertisement for eye donation on television or a newspaper helps to blind people around us and more people can aware of this noble cause.
8. (a) What type of spectacles should be worn by a person having the defect of myopia as well as hypermetropia.
(b) The far point of a myopic person is 150 cm. What is the nature and the power of the lens required to correct the defect?
(c) With the help of a ray, a diagram showing the formation of image by:
(i) a myopic eye
(ii) Correction of myopia by using an appropriate lens.
Javoblar (a) Spectacles of the concave lens or diverging lens should be worn by a person having the defect of myopia and converging lens for hypermetropia.
(b) The far point of a myopic person is 150 cm. A person with myopia can see nearby objects clearly but cannot see distant objects distinctly. A person with this defect has a far point nearer than infinity. A concave lens or diverging lens of suitable - ve power will bring the image back on to the retina and thus the defect is corrected.
9. A person's image when seen through a stream of hot air rising above a fire disappeared to waver. Tushuntiring.
Javoblar The apparent random wavering of objects seen through a stream of hot air rising above a fire or a radiator because the air just above the fire becomes hotter than the air further up.
The hotter air is lighter or less dense than the cooler air above it, and has a refractive index slightly less than that of the cooler air. Since the physical conditions of the refracting medium are not stationary, the apparent position of the object, as seen through the hot air, fluctuates. This wavering is thus an effect of atmospheric refraction on a small scale in our local environment.
10. (a) Describe an activity along with a level diagram of the phenomenon of dispersion through a Prism.
(b) Explain in brief the formation of the rainbow with the help of the figure.
Javoblar (a) Activity - Take a thick sheet of cardboard and make a small hole or narrow slit in its middle.
Allow sunlight to fall on the narrow slit. This gives a narrow beam of white light.
Now, take a glass prism and allow the light from the slit to fall on one of its faces.
Turn the prism slowly until the light that comes out of it appears on a nearby screen.
We will find a beautiful band of colours due to the dispersion of light.
Faoliyat:. Place a strong source (S) of white light at the focus of a converging lens (L1). that provides a parallel beam of light.
. Allow the light beam to pass through a transparent glass tank (T) containing clear water.
. Allow the beam of light to pass through a circular hole (c) made in cardboard. Obtain a sharp image of the circular hole on a screen (MN) using a second converging lens (L2).
.Dissolve about 200 g of sodium thiosulphate in about 2 L of clean water taken in the tank.
Add about 1 to 2 mL of concentrated sulphuric acid to the water.
We can observe the blue light from the three sides of the glass tank that is due to scattering of short sulphur particles. The colour of the transmitted light from the fourth side of the glass tank facing the circular hole, at first the orange red colour and then bright crimson red colour on the screen.
Two chemicals used in this activity are natriy tiosulfat va sulfat kislota .
12. (I) Define dispersion. How does a prism disappear white light? Which colour of light bends the most and the least?
(II) A narrow beam of white light is passing through a glass prism. Trace it on your answer sheet and show the path of the emergent beam as observed on the screen.
(a) Write the name and the cause of the phenomenon observed.
(b) Where else in nature in this phenomenon observed.
(c) Base on the observation, state the conclusions which can be drawn about the constitution of white light.
Javoblar (I) The splitting of light into its component colours is called dispersion.
White light is dispersed into its seven-colour components by a prism. Different colours of light bend through different angles with respect to the incident ray, as they pass through a prism. It is due to different wavelengths of different colour.
The red light bends the least while the violet the most.
(a) The phenomenon is a dispersion of light and it caused due to different colours of light bend through different angles with respect to the incident ray as they have different wavelengths.
(b) Rainbow after rain.
(c) The prism has probably split the incident white light into a band of seven colours. The sequence of colours are Violet, Indigo, Blue, Green, Yellow, Orange, and Red. (VIBGYOR)
13. State the natural phenomenon behind the formation of the rainbow? Explain the phenomenon. Name a device that can be used to observe such a phenomenon in the laboratory? If you are facing a rainbow in the sky, what is the position of the sun with respect to your position?
Javoblar The natural phenomenon behind the formation of rainbow is dispersion.
The splitting of light into its component colours is called dispersion.
White light is dispersed into its seven-colour components by a prism. Different colours of light bend through different angles with respect to the incident ray, as they pass through a prism. It is due to different wavelengths of different colour.
The red light bends the least while the violet the most.
Prism is used to observe dispersion in the laboratory.
A rainbow is always formed in a direction opposite to that of the Sun. Therefore the position of the Sun behind me.
14. An old person is unable to see clearly nearby objects as well as distinct ob'ektlar.
(a) What defect of vision is the suffering from?
(b) What kind of lens will be required to see clearly the nearby as well as distant objects? Give reasons.
Javoblar (a) The defect of vision is Presbyopia in which he finds it difficult to see nearby objects comfortably and distinctly without corrective eye-glasses. This defect is called Presbyopia.
(b) A common type of bi-focal lenses consists of both concave and convex lenses.
Reason: It arises due to the gradual weakening of the ciliary muscles and diminishing flexibility of the eye lens. So a person may suffer from both myopia and hypermetropia. A common type of bi-focal lenses consists of both concave and convex lenses. The upper portion consists of a concave lens. It facilitates a distant vision. The lower part is a convex lens. It facilitates near vision.
Do other animals suffer from myopia or hypermetropia? - Biologiya
Refractive errors and their effects on visual evoked potentials
Ruchi Kothari 1 , Pradeep Bokariya 2 , Smita Singh 3 , Purvasha Narang 3 , Ramji Singh 4
1 Department of Physiology, MGIMS, Sevagram, Wardha, Maharashtra, 3Department of Physiology, AIIMS, Patna, Bihar, India
2 Department of Anatomy, MGIMS, Sevagram, Wardha, Maharashtra, 3Department of Physiology, AIIMS, Patna, Bihar, India
3 Department of Ophthalmology, MGIMS, Sevagram, Wardha, Maharashtra, India
4 Department of Physiology, AIIMS, Patna, Bihar, India
|Date of Submission||15-May-2013|
|Date of Acceptance||25-Jun-2013|
|Date of Web Publication||3-Dec-2013|
Department of Physiology, MGIMS, Sevagram, Wardha - 442 102, Maharashtra
Source of Support: None, Conflict of Interest: Hech kim
In view of the increasing use of visual evoked potentials (VEP) technique in neuro-ophthalmological diagnosis, it was thought pertinent to appraise the changes brought about in VEPs in the presence of refractive error (RE) as studied by the vision researchers and neurophysiologists. The purpose of this review was to provide a comprehensive quintessence of the work carried out in this fi eld with an attempt to summarize the previous concepts, recent perspective and current notion about the value of RE in electrophysiologic testing particularly the VEP technique.
Kalit so'zlar: Defocus, refractive errors, visual evoked potential
|How to cite this article:|
Kothari R, Bokariya P, Singh S, Narang P, Singh R. Refractive errors and their effects on visual evoked potentials. J Clin Ophthalmol Res 20142:3-6
|How to cite this URL:|
Kothari R, Bokariya P, Singh S, Narang P, Singh R. Refractive errors and their effects on visual evoked potentials. J Clin Ophthalmol Res [serial online] 2014 [cited 2021 Jun 24]2:3-6. Available from: https://www.jcor.in/text.asp?2014/2/1/3/122625
Visually evoked cortical response testing has been one of the most exciting clinical tools to be developed from neurophysiologic research and has provided us with an objective method of identifying abnormalities of the afferent visual pathways.
Visual evoked potentials (VEPs) reflect electrical phenomena occurring during the visual processing and are a graphic illustration of the cerebral electrical potentials generated by the occipital cortex evoked by a defined visual stimulus.  Therefore, VEPs can be used both in research and in clinical practice to elucidate the function of the visual system.
It is known that the technical and physiological factors such as pupil diameter, refractive errors (REs), type of stimulus, age and sex, electrode position and anatomical variations may affect VEP.  It is assumed that RE cause defocus. Defocusing may affect the VEP, which if allowed to persist, can result in corresponding neurological changes.
It was perceived that there was no clear cut presumption with regards to how actually does the RE alters the visually evoked response of the brain, whether the VEPs are more affected by myopia or hypermetropia and to what extent the degree of RE would affect the VEPs. Therefore, we made an attempt to review the various aspects related to the effects of RE on VEPs.
Beginning with background reading about the topic, we traced the specific resources, extensively searched the literature, analyzed the shortcomings and strengths of various workers, tabulated their methodologies and findings in chronological manner and tried to derive at an inference incorporating the previous, recent and finally our own perspective regarding the relationship of VEPs with REs.
Multiple database searches using MedLine, Google scholar, EMBASE and PubMed were conducted to identify all the previous as well as the recent studies and publications pertinent to this issue. All identified documents were examined and those that were relevant were retrieved for inclusion in the review. The relevant reports were skimmed, retrieved compiled and important conclusions from the studies were laid down in proper chronology. The methodologies and findings of various authors were tabulated for a quick glance and to make easy comparisons between them. Reference lists of retrieved documents were hand searched to identify the additional publications. Then a critical analysis of the relationship among different works was performed and finally this research was coupled to our own work.
Minute neural discharges that occur in visual cortex upon brief exposure of the eye to patterned stimuli after monitoring by topical scalp electrodes, amplification and summation produce characteristic waveform that exhibits a relationship to retinal image clarity. A systematic relationship was first established long back.  They observed that the amplitude for both a negative wave appearing at 80-100 ms after a flash of patterned target and a positive wave following this flash by 180-200 ms was greater with retinal image clarity and lessened with its degradation over a wide range of dioptic values.
The amplitude of the response in a pattern reversal VEP is dependent on the visual system's ability to resolve the pattern and on the degree of retinal image focus. Small errors of refraction tend to reduce the average amplitude of the waves of VEPs. A quantified documentation was provided  who found the VEP amplitude to be decreased 25% per diopter (D) of defocus and the effect was appreciable for 0.25 D. They employed a rotating polaroid in conjunction with a checker pattern made of polaroid strips, in which the intensity for each neighboring check varied sinusoidally in time. The overall intensity of light transmitted through the pattern therefore remained constant. The subject's eye was situated 85 cm from the plane of the pattern.
The VEP is more sensitive to small refractive changes than electroretinogram (ERG), perhaps because the VEP heavily emphasizes the foveal region while the ERG is more broadly representative of the entire stimulus field.
Considerable attention was given in the past to the use of checkerboard-pattern stimuli in the study of the VEPs in subjects as a technique for determining REs. Duffy and Rengstorff.  electronically subtracted the response to light from the response to pattern plus light that yielded a residual contour response. Working at a 20 feet refraction distance, they performed an initial scan over a wide range of spherical lens values with large increments on relatively large checker squares, 10 min of arc. They finalized the spherical lens measurement by use of small lens increments on a finer checker square pattern (2.5´). They claimed precision of spherical refraction of 0.25 D. The value determined was found to be more myopic or less hyperopic than that established by the conventional refractive techniques.
Reduction in amplitude of the VEP with RE was also reported.  They showed that there is consistently greater reduction in VEP amplitude for small amounts of plus lens defocus than for minus and it showed that subjects partially accommodated for minus lens. They found that decrease in amplitude in non-cycloplegic refraction measurements seem to occur more rapidly for plus lens than for minus and it is thought to be due to the partial correction of defocus brought about by accommodative effort of the subject.
The REs blur the stimulus and blurred vision also has been shown to decrease the amplitude of the conventional pattern reversal VEP.  Large REs, introduced by the use of ophthalmic lenses, cause the waves to approach zero amplitude. Collins va boshqalar al.  studied the effect of introduced REs on the VEP on five women and eight men aged 19-45 years.
REs were created by introducing the following combined standard lenses: (+2.00 DS + 2.00 DC × 90°), (+1.00 DS + 1.00 DC × 90°), (.00 DS .00 DC × 90°) and (.00 DS .00 DC × 90°) diopters. Using 3° radius field stimulation and 12-min checks, monocular pattern-reversal VEPs were recorded without and then with each introduced RE by a computer-based data collection system and compared with previously established normal values. There was a pronounced effect on the P100 component of the VEP with these introduced REs.
The P100 latency was abnormally prolonged in 31% (5/16) of recordings with the (.00 DS .00 DC × 90°) diopter lens and in 87.5% (14/16) with the (+2.00 DS + 2.00 DC × 90°) diopter lens. The maximum P100 latency was 126 ms. For all other recordings, the P100 latency was less than 113 ms, but there was considerable temporal dispersion and reduction in amplitude of the P100 component, especially for the convex lenses. Indeed, the VEP was almost abolished in some of the recordings when a (+2.00 DS + 2.00 DC × 90°) diopter lens was used. Their study, using the pattern-reversal method, illustrated the significant changes in absolute and relative latency of the P100 component when Res, which approximated to those found in the population at large, were introduced to defocus a small stimulus field and high spatial frequency pattern. This effect was seen to be greatest for REs of + 2.00 DS + 2.00 DC × 90° diopters.
Pattern defocusing has been used to evaluate the contribution of different spatial frequency components in checks to VEP latency. Latency shifts with increasing blur (.50 to +2.50) were determined  for sinusoidal grating and check patterns. The effect of blur was found to be more for the higher spatial frequencies. Zislina va boshqalar al.  in their studies with congenital myopia have shown significant deviations from reference of component P100.
REs were induced  in normal subjects by means of positive D lenses to reduce visual acuity (VA) from an initial level of 20/20 to 20/100 and then to 20/200. Pattern visual evoked potentials (PVEPs) were recorded at each of these three levels of VA using high contrast checkerboard stimuli subtending 11´ and 42´ of visual arc. Their findings confirmed the need to take REs into account because latencies fell outside normal limits with decreased VA.
Reduction of VA or of the contrast of the stimulus induces a prolongation of the pattern reversal visual evoked potential (PR-VEP) latencies, perhaps because these conditions cause deterioration of the visual capacity to recognize objects and may preferentially activate the slower central retina channel. The PR-VEP was obtained  with a video stimulator and three kinds of stimuli: Total video field, video with a central scotoma and a restricted central stimulus. The subjects were tested under conditions of normal (20/20) and reduced VA (20/200) with 14´ and 56´ checks and 60% contrast and under conditions of normal VA (20/20) with 14´ checks and with stimulus contrast of 60% and 25%. Blurring increased latencies and decreased amplitudes only with the 14´ checks stimulus but not with 56´ checks and the amplitudes obtained with the central stimulus became greater than those obtained with a central scotoma. Reducing contrast increased only latency and there was no difference between amplitudes obtained with a central stimulus or a central scotoma. They deduced that blurring small checks induces a preferential stimulation of receptors in the central retina, but the same effect was not observed when stimulus contrast was reduced. Thus, prolongation of latency and decreased amplitude with a reduction in VA was established in their study.
In their study, Perlman va boshqalar al.  investigated the correlation between reduced VA and VEP in volunteers with normal corrected VA and in patients suffering from inherited macular degeneration or from age related macular degeneration. In both groups of patients suffering from macular dysfunction, pattern reversal VEP was very subnormal and was characterized by prolonged implicit time. These findings indicated that the PVEP directly correlates with foveal function. Therefore, they suggested that recordings of PVEP can be used to differentiate between RE and macular disorders as causing reduction in VA when other clinical signs are missing or not available.
Li va boshqalar al.  tried to evaluate the P100 latency of VEP according to refraction. They studied 28 patients (12 males, 16 females) with myopia. Subjects were divided into three groups (mild, moderate, severe myopia) according to refraction and they evaluated the results of VEP studies. The Mean values of refraction and latency (P100) of naked eyes were -4.27 DS, 103.95 ms and those of corrected eyes (in glasses) were -0.25 DS, 100.59 ms. Respectively, in mild, moderate, and severe myopia, the P100 latency of naked eyes were 101.27 ms, 102.59 ms, 107.99 ms and those of corrected eyes were 98.33 ms, 100.58 ms, 102.19 ms respectively (P & lt 0.05). There was significant negative correlation between refraction and P100 latency in myopia.
Marr va boshqalar al.  undertook a retrospective case review and recruited 112 children with age less than 10 years presenting over 3 years who were found to have high myopia (defined as one or both eyes demonstrating six diopters spherical equivalent or more of myopic RE on retinoscopy). They concluded that high myopia in early childhood is strongly associated with systemic and ocular problems. In 54%, there was an underlying systemic association with or without further ocular problems (e.g., developmental delay, pre-maturity, Marfan, Stickler, Noonan, Down syndrome) and in the remaining 38% there were further ocular problems associated with the high myopia (e.g., lens subluxation, coloboma, retinal dystrophy, anisometropic amblyopia).
Marr va boshqalar al.  reviewed 114 consecutive children under 10 years of age with high hypermetropia (greater than + 5.00 DS) during a 5-year period and reported that high hyperopia has a similar incidence of associated ocular abnormalities as high myopia.
To understand how REs affect multifocal visual evoked potential (mfVEP) responses, monocular mfVEP responses were obtained using a pattern reversal dartboard display .  The right eye was tested under simulated RE. For the simulated RE condition, significant centrally located abnormalities were seen for all subjects. They concluded that factors such as uncorrected REs can produce apparent field defects on the mf VEP.
A very recent study conducted by Anand va boshqalar al.  examined effects of uncorrected REs in a short-duration transient visual evoked potential system and investigated their role for objective measurement of RE. REs were induced by means of trial lenses in 35 emmetropic subjects. A synchronized single-channel electro encephalogram was recorded for emmetropia and each simulated refractive state to generate 21 VEP responses for each subject. P100 amplitude (N75 trough to P100 peak) and latency were identified by an automated post-signal processing algorithm. They construed that induced hypermetropia and myopia correlated strongly with both P100 amplitude and latency.
Most of these studies have been reported in western populations and no such comparative study is available in Indian population. Since, there are differences as regards to the age of detection, accuracy of correction and regularity of usage of correcting glasses, a recent study  was conducted to estimate the effect of RE on VEP recordings in Indian population. To test the hypothesis that the changes in VEP due to REs in Indian population are different from western population, pattern reversal VEP recordings were performed in a total of 50 hypermetropics and 50 myopics having age in the range of 18-40 years. The subjects having astigmatism (>0.5 DC) and RE of more than 5 D were excluded in the study. They were investigated for VEP recordings with and without glasses. Their results were compared with those of 50 age and sex matched controls. P100 latency was increased and amplitude decreased with and without correction of RE. The statistical analysis revealed a significant difference (P < 0.05) in latency of P100 and amplitude of P100 between controls and myopics with glasses and highly significant difference (P < 0.001) between controls and myopics without glasses so, VEPs were affected in Indian subjects with RE irrespective of correction given, but more so without correction.
The difference in P100 latency and amplitude between controls and hyperopics with glasses and those without glasses were found to be non-significant in this study.
A RE develops when there is lack of coordination among the factors required for the growth of the eye and for the eye to become emmetropic like changes in refractive components and in eye size. A myopic eye is generally larger than emmetropic or hyperopic eyes and changes in scleral tissue may be the factor when emmetropization does not occur. Animal studies have shown that poor image quality on the retina can elicit a signal to sclera tissue components to strengthen or weaken in an attempt to move the retina to the best location for a clear image.
Scleral remodeling causes axial lengthening that occurs in myopia the scleral tissue is weakened and thins. In progressive myopia existing collagen is degraded, the production of new collagen is reduced and matrix proteoglycans are lost. , So in this way, if we recollect the physiological changes occurring in the development of myopia, substantial explanation to the above finding unfurls.
To conclude, the observations of the studies [Table 1] in the past as well as the recent research in this field suggest that the RE blur the stimulus and cause defocus, which lead to significant changes in VEP (P100 latency and amplitude) in the presence of RE. As per our perspective, among the REs, VEPs seem to be more affected by myopia than hypermetropia. However, the principal cause in both is the degree of defocusing of the image produced by the RE.
If pattern stimuli are to be used in VEP investigation, it is important that a patient be tested with RE corrected. REs tend to affect the interpretation of the VEP results. Therefore in performing the VEP study, one should consider the refraction and VA.