Demo on Human Eye and their parts and detail

What is Human eyes their benefits and advantage and disadvantage

2. INTRODUCTION
Human eye
Thehumaneyeisasensoryorganresponsibleforvision,providinguswiththe
abilitytoperceivelightanddetectshapes,colors,andmovement.
Itactslikeacamera,enableustocapturethecolourfulpictureofthe
surroundings.

3. Structure of Human Eye

4. Parts of Human Eye:-
Sclera:
Itistheoutercovering,aprotective
toughwhitelayercalledthesclera
(whitepartoftheeye).
Cornea:
Thefronttransparentpartofthescleraiscalledthecornea.Lightenterstheeye
throughthecornea.
Iris:
Adarkmusculartissueandring-likestructurebehindthecorneaisknownas
theiris.Thecolouroftheirisactuallyindicatesthecolouroftheeye.Theiris
alsohelpsregulateoradjustexposurebyadjustingtheiris.
Pupil:Asmallopeningintheirisisknownasapupil.Itssizeiscontrolledwith
thehelpofiris.Itcontrolstheamountoflightthatenterstheeye.

5. Lens:
Behindthepupil,thereisatransparent
structurecalledalens.
Bytheactionofciliarymuscles,itchangesits
shapetofocuslightontheretina.
Itbecomesthinnertofocusondistant
objectsandbecomesthickertofocusonthe
nearbyobjects.
Retina:
Itisalight-sensitivelayerthatconsistsofnumerousnervecells.Itconverts
imagesformedbythelensintoelectricalimpulses.Theseelectricalimpulsesare
thentransmittedtothebrainthroughopticnerves.
Opticnerves:Opticnervesareoftwotypes.Theseincludeconesandrods.
Cones:Conesarethenervecellsthataremoresensitivetobrightlight.
Theyhelpindetailedcentralandcolourvision.
Rods:Rodsaretheopticnervecellsthataremoresensitivetodimlights.
Theyhelpinperipheralvision.
Atthejunctionoftheopticnerveandretina,therearenosensorynervecells.Sono
visionispossibleatthatpointandisknownasablindspot.

6. FUNCTIONING OF HUMAN EYES:
Theeyeofahumanbeingislikeacamera.Muchliketheelectronicdevice,the
humaneyealsofocusesandletsinlighttoproduceimages.Sobasically,light
raysthataredeflectedfromorbydistantobjectslandontheretinaafterthey
passthroughvariousmediumslikethecornea,crystallinelens,aqueoushumor,
thelens,andvitreoushumor.
They help in peripheral vision.

7. The concept here though is that as the light rays move through the various
mediums, they experiencerefraction of light.
Well, to put it in simple terms, refraction is nothing but the change in direction
of the rays of light as they pass between different mediums.
The table below shows the refractive indices of the various parts of the eye.

8. Havingdifferentrefractiveindexesis
whatbendstheraystoformanimage.
Thelightraysfinallyarereceivedand
focusedontheretina.Theretina
containsphotoreceptorcellscalled
rodsandconesandthesebasicallydetecttheintensityandthefrequencyofthe
light.Further,theimagethatisformedisprocessedbymillionsofthesecells,
andtheyalsorelaythesignalornerveimpulsestothebrainviatheopticnerve.
Theimageformedisusuallyinvertedbutthebraincorrectsthisphenomenon.
Thisprocessisalsosimilartothatofaconvexlens.
DefectsofHumanEye
ANormaleyecanseeobjectsclearlyatanydistancebetween25cmandinfinity
fromtheeye.Sometimes,ahumaneyegraduallyloseitspowerof
accommodation.Thanwecannotseetheobjectclearlyourvisionbecome
defective.Therearemainlyfourcommondefectofvisionwhichcanbe
correctedbytheuseofsuitableeyeglasses.ThereareMyopiaornear
sightedness,Hypermetropiaorfar-sightedness,Presbyopia,Astigmatism.

9. MyopiaOrShort-sightedness
Inthisdefectapersoncanseenearbyobjectclearlybutcannotseefaroff
objectclearly.Here,eithertheeyeballbecomestoolongerorthefocallengthof
theeyelensbecometooshort.
Itcanbecorrectedbyusingaconcavelensofsuitablefocallength.Focal
lengthofthecorrectinglens=Distanceofthefarpoint
fromtheeye.

10. HypermetrophiaorLong-sightedness
Inthisdefectapersoncanseethefaroffobjectclearlybuthe/shecannotsee
nearbyobjectdistinctly.Here,eithertheeyeballbecomestooshortorthefocal
lengthofthefocallengthofthefocallengthoftheeyelensbecomestoolarge.
Itcanbecorrectedbyusingconvexlensofsuitablefocallength.Focallength
ofcorrectinglens=yD/y-DWherey=Distanceofthenearpointfromthe
defectiveeye

11. Presbyopia
Inthisdefect,apersoninoldagecannot
Readcorrectlyduetothestiffeningofthe
Ciliarymusclesandthedecreaseinflexibilityofthe
eyelens.
Astigmatism
Itisadefectofvisioninwhichaperson
cannotsimultaneouslyseeboththehorizontal
andverticalviewsofanobjectwiththesameclarity.
Itisduetotheirregularcurvatureofthecornea.
Itcanbecorrectedbyusingacylindricallens.

12. Cotaract
Itisduetothedevelopmentofhazyor
opaquemembraneovertheeyelenswhich
resultsinthedecreaseorlossofvision.
Itcanbecuredbysurgery.
BlindSpotAndYellowSpot
Intheregionwheretheopticnerveenterthe
eyeball,therearenotrodsandcones.This
regionistotallyinsensitivetolightandiscalled
blindsport.
Yellowspothasmaximumconcentrationof
lightsensitivecells.Itissituatedincenter
oftheretina.

13. ColourBlindness
Apersonwhocannotdistinguishbetweenvariouscolourbutcanseewell
otherwise,issaidtobecolour-blind.Itisduetolackofsomeconesinretinaof
theeyes.
ExampleofanIshiharacolortestplate.Withproperlyconfiguredcomputer
displays,peoplewithnormalvisionshouldseethenumber"74".Manypeople
whoarecolorblindseeitas"21",andthosewithtotalcolorblindnessmaynot
seeanynumbers.