ANATOMY OF EYE n.pdf

human eye

2. THE EYE
•Theeyeisorganofsightwhichissituatedin
theorbitalcavity.
•ItissuppliedbytheOpticNerve(2
nd
cranial
nerve.
•Shape-spherical(2.5cmindiameter)

3. STRUCTURE OF THE EYEBALL
1.Wallofeyeball.
2.Lighttransmittingmedia(or)refractive
media

6. WALL OF THE EYEBALL
1.Outerlayer(fibrouscoat):ScleraandCornea
2.Middlelayer(vascularcoat):Choroid,Ciliary
bodyandIris
3.Innerlayer(nervouscoat):Retina

7. Sclera and Cornea
•Scleraorthe“whiteoftheeye”formsthe
outermostlayeroftheeyeball
•Theanterioronesixthpartofthesclerais
transparentandisknownascornea.The
corneaisdescribedasthe“windowofthe
eye”
•Lightrayspassthroughthecorneatoreachthe
retina.

8. Choroid
•Choroidisathinpigmentedmembrane,dark
brownincolorwhichissituatedinbetween
sclera(externally)andretina(internally).

9. CiliaryBody
•Ciliarybodyisthecontinuationofchoroid
consistingofsmoothmusclefibers,i.e,cilliary
muscles.
•Ciliarybodycontainssuspensoryligamentfor
attachingthelensinposition.

10. Iris
•Irisisthepigmentedmembranesurroundsthe
pupil
•Itarisesfromthemarginofciliarybodyand
formsadarkcenteredopeningcalledpupil.
•Thespacebetweencornea(infront)andthe
lens(behind)istheanteriorsegmentwhichis
filledwithaclearfluid,theaqueoushumor.

11. Retina
•Retinaistheinnermostlayeroftheeyeball.
•Theoutersurfaceoftheretina,formedby
pigmentcells,isattachedtochoroid.
•Therearetwotypesofphotoreceptorcellsin
thehumaneyerodsandcones.

12. Cont..
•Thesecellscontainsphotosensitivepigments
(Rods-Rhodopsin,Cones–iodopsin)involved
intheconversionoflightraysintonerve
impulses.

14. Cont..
•Thesmallareaofretinawheretheopticnerve
leavestheeyeistheopticdiscortheblind
spot.Ithasnolightsensitivecells(Rodsor
Cones).

15. Cont..
•Lateraltotheopticdiscadepressioncalled
maculalutea.
•Thecenterofmaculaisagaindepressedto
formthefoveacentralis.Itcontainscones
onlyandisthesiteofmaximumacuityof
vision.

16. BLOOD SUPPLY
•Arterialbloodis
suppliedbybranches
ofophthalmicartery
(ciliaryarteries&
centralretinalartery)
•Venousdrainagea
numberofveins
includingthecentral
retinalvein.

17. 2. LIGHT TRANSMITTING MEDIA (OR)
REFRACTIVE MEDIA
1.Aqueous humor
2.Vitreous humor
3.Lens

19. Cont..
•Theeyekeepsitsshapebecauseofintraocular
pressure(15-16mmHg)exertedbythe
vitreousbodyandtheaqueousfluid.It
remainsconstantthroughoutthelife.

20. Lens
•Thelensoftheeyeballiscrystallineinnature.
•Itissituatedbehindthepupil.
•Itisbiconvex,transparentandelasticin
structure.
•Lensrefractslightraysandhelpstofocusthe
imageoftheobjectonretina.

21. Cont..
•Lightfromasinglepointofadistantobject
andlightfromasinglepointofanearobject
beingbroughttoafocusbychangingthe
curvatureofthelens.

22. Accessory Visual Structures
of The Eye

23. Accessory Visual Structures
Theaccessoryvisualstructuresarethe
protectingandsupportingstructuresofthe
eye.Itincludes:-
1.Eyebrow
2.Eyelidsandeyelashes
3.Conjuctiva
4.Lacrimalapparatus

24. Eyebrow
•Theeyebrowisanareaofthick,shorthairs
abovetheeye.
•Themainfunctionistopreventsweat,water,
andotherdebrisfallingintotheeye,butthey
arealsoimportanttohumancommunication
andfacialexpressions.

25. Eyelids & Eyelashes
•Theeyelidsaretwomovablefoldsoftissue
situatedaboveandbelowthefrontofeach
eye.
•Shadetheeyesduringsleep,protecttheeye
fromexcessivelightandforeignobjects,and
spreadlubricatingsecretionsoverthe
eyeballs.
•Ontheirfreeedges,thereareshortcurved
hairs,theeyelashes.

26. Conjuctiva
•Itisafinetransparentmembranethatlines
theeyelidsandthefrontoftheeyeball.
•Themedialandlateralanglesoftheeye
wheretheupperandlowerlidscometogether
arecalledmedialcanthusandlateralcanthus.

27. Eyelid Margins
•Alongtheedgesofthelidsarenumerous
sebaceousglands(Meibomianglands),some
withductsopeningintothehairfolliclesofthe
eyelashes.
•Theysecreteanoilymaterial,spreadoverthe
conjuctivabyblinking,whichdelays
evaporationoftears.

29. LacrimalApparatus
Foreacheye,thisconsistsof:-
•1lacrimalglandanditsducts
•2lacrimalcanaliculi
•1lacrimalsac
•1nasolacrimalduct

30. LacrimalApparatus

31. Cont..
•Thelacrimalglandislocatedwithintheorbit
abovethelateralendoftheeye.
•Itcontinuallyreleasesfluid(tears)whichcleanses
andlubricateseye'ssurfaceandkeepitmoist.
•Tearsarecomposedofwater,mineralsalts,
antibodiesandlysozyme.
•Thetearsleavethelacrimalglandbyseveralsmall
ductsandpassoverthefrontoftheeyeunder
thelidstowardsthemedialcanthuswherethey
drainintothetwolacrimalcanaliculi;the
openingofeachiscalledpunctum.

33. Cont..
•Thetwocanaliculilieoneabovetheother,
separatedbyasmallredbody,theCaruncle.
•Thetearsthendrainintothelacrimalsac,
whichistheupperexpandedendofthe
nasolacrimalduct.
•Nasolacrimalductisamembranouscanal
approx2cmlong,extendingfromthelower
partofthelacrimalsactothenasalcavity.

34. Cont..
Thefluidthatfillstheconjuctivalsacisa
mixtureoftearsandtheoilysecretionof
mebomiumglands.
Thefunctionsofthisfluidinclude:-
a)Washingawayirritatingmaterials,eg.Dust.
b)Lysozymepreventsmicrobialinfection.
c)Itsoilinessdelaysevaporationandprevents
dryingoftheconjuctiva.

35. Six extrinsic eye muscles move each eye:
1.Lateralrectus–movestheeyeoutward,away
fromthenose
2.Medialrectus–movestheeyeinward,toward
thenose
3.Superiorrectus–movestheeyeupwardand
slightlyoutward
4.Inferiorrectus–movestheeyedownwardand
slightlyinward
5.Superioroblique–movestheeyeinwardand
downward
6.Inferioroblique–movestheeyeoutwardand
upward

36. Six extrinsic eye muscles move each eye:

37. PHYSIOLOGY OF VISION

38. Physiological Events Of Vision
1.Refractionoflightenteringtheeye
2.Focusingofimageontheretinaby
accommodationoflens
3.Convergenceofimage
4.Photo-chemicalactivityinretinaand
conversionintoneuralimpulse
5.Processinginbrainandperception

39. 1. Refraction of light entering the eye:
•Lightwavetravelsparalleltoeachotherbut
theybendwhenpassesfromonemediumto
another.Thisphenomenoniscalledrefraction.
•Innormaleye,afterrefractionfromdifferent
mediums,lightwaveisfocusedonretina.

40. 2. Accommodation of lens to focus image:
•Accommodationisareflexprocesstobring
lightraysfromobjectintoperfectfocuson
retinabyadjustingthelens.
•Whenanobjectlyinglessthan6meterawayis
viewed,imageformedbehindretina.Butdue
toaccommodationoflensimageformedin
retinaandwecanseetheobject.

41. Cont..
•Whennearerobjectisviewed,ciliarymuscle
contractandlensbecomethickwhichcauses
focusoncloserobject.
•Whendistantobjectisviewed,ciliarymuscles
relaxes,andlensbecomethinner,dueto
whichimageformsonretina.
•Thenormaleyeisabletoaccommodatelight
fromobjectabout25cmtoinfinity.

43. 3. Convergence of
image:
•Humaneyehavebinocularvision,itmeans
althoughwehavetwoeye,weperceivesingle
image
•Inbinocularvision,twoeyeballturnsslightly
inwardtofocusacloseobjectsothatboth
imagefallsoncorrespondingpointsonretina
atsametime.Thisphenomenoniscalled
convergence.

44. 4. Photo-chemical activity in retina and
conversion into neural impulse
•Eacheyecontains125millionrodswhichcontains
lightsensitivepigment-rhodopsinand7million
conecellswhichcontainiodopsin.
•Whenlightisfallsonrodcell,itisabsorbedby
rhodopsinanditbreaksintoscotopsinand11cis-
retinal.Theprocessisknownasbleaching.
•Hyperpolarizedrodcellstransmittheneuralsignal
tobipolarcell.
•Bipolarcellandganglioncellprocesstheneural
signalandgenerateactionpotentialtotransmitto
brainviaopticnerve.

46. 5. Processing of image in brain and
perception:
•Retinacontains5typesofcellsandtheyare
interconnectedbysynapse.
•Thesecellsarephotoreceptorcells(rodand
cone),bipolarcell,ganglioncell,horizontalcell
andamacrinecell.
•Allvisualinformationoriginatesinretinadue
tostimulationofrodsandconesareconveyed
tobrainthroughopticnerve.

48. Cont..
•Thenervefiberofganglioncellsfromboth
eyescarriesimpulsealongtwoopticnerve.
•Theopticnervesmeetsatopticchiasma
wherefibersfromnasalhalfofeachretina
cross-overbutfibersfromtemporalhalfof
eachretinadonotcross-over.
•Theopticnerveaftercrossingthechiasmais
calledasoptictract.

49. Cont..
•Eachoptictractcontinuesposteriorlyand
synapsewithneuroninthalamuscalledlateral
geniculatebodywhichprojecttoprimaryvisual
cortexinoccipitallobeofcerebrumandimageis
perceived.

52. ERRORS OF REFRACTION
•Refractionresultsinthefocusingofimageon
theretinaoftheeye,permittingvision.
•Inrefractiveerrors,visionisimpairedbecause
ashortenedorelongatedeyeballprevents
lightraysfromfocusingsharplyontheretina.
•Blurredvisionfromrefractiveerrorscanbe
correctedwitheyeglassesorcontactlenses.

53. Types of refractive errors:
1.Myopia
2.Hypermetropia(Hyperopia)
3.Astigmatism
4.Presbyopia

54. 1. Myopia
•Near-sightedness
•Problemseeingobjectsfaraway
•Distancebetweenlensandretinatoolarge
•Lightfocusedinfrontofretina
•Correctwithconcave(diverging)lenses

55. 1. Myopia

56. 2. Hypermetropia
•Far-sightedness
•Problemseeingcloseobjects
•Distancebetweenlensandretinatoosmall
•Lightfocusedbehindretina
•Correctedwithconvex(converging)lenses

57. 2. Hypermetropia

58. 3. Astigmatism
•Eyecannotfocusanobject’simageona
singlepointonretina
•Corneaisovalinsteadofspherical
•Causesblurredvision
•Sometypescanbecorrectedwith
cylindrical/ovallenses

59. 3. Astigmatism

60. 4. Presbyopia
•Presbyopiaisthegraduallossofeye’sability
tofocusonnearbyobjects.
•Itoccursduetohardeningoflensdueto
ageing.
•Itusuallybecomesnoticeableinearlytomid-
40sandcontinuestoworsenuntilaroundage
65years.

61. 4. Presbyopia

62. PATHOLOGICAL TERMS
•Glaucoma-Itisagroupofeyeconditionsthat
damagetheopticnerve.Thisdamageisoften
causedbyanabnormallyhighpressureinthe
eye(IOP).
•Cataract-Itiscloudingformsinlensdueto
denaturingoflensprotein.Itobstructs
passageoflight.

63. Cont..
•Conjutivitis-Inflammation or infection of the
outer membrane of the eyeball and the inner
eyelid.
•Strabismus-Squint, also called strabismus, is
where the eyes point in different directions.