Human eye

1. Human Eye:Anatomy, parts and structure
 The eye isthe photo-receptororgan.
 Size and shape: Human eye isspherical about2.5 cm indiameter.
 Location: it issituatedonan orbitof skull andissuppliedbyopticnerve.
 There are 6 setsof muscles attachedtooutersurface of eye ball whichhelpstorotate itin
differentdirection.
 Four setsof these musclesare straightmuscles;superior,inferior,medial andlateral rectal
muscle andtwo setsare oblique muscles;superiorandinferiorobliquemuscles.
 Structurallytwoeyesare separatedbutsome of theiractivitiesare coordinatedsothatthey
functionsasa pair.
Anatomical structure of Eye
Eye ball consistsof three layers
1. Outerfibrouslayer:Sclera,corneaandconjunctiva
2. Middle vascularlayer:ciliarybody,choroidandiris
3. Innerlayer:retina
I. Outer fibrouslayer:

2. It consistsof followingparts.
1. Sclera:
 It isoutermostsupportinglayerconsistsof thickmembraneof toughfibrousconnective tissue.
 It covers5/6 parts of eye ball.
 It maintainsthe shape of eye andprovide attachmenttothe extrinsicmuscle of eye
2. Cornea:
 It isa thintransparentfrontpart of sclera.
 It formsa slightbulge atthe frontand coversan anterior1/6 part of sclera.
 Corneaisavascular andabsorbsoxygen fromair.
 It refractslightto focuson retina.
3. Conjunctiva:
 It isa thintransparentlayerthatcoversthe cornea.
 It isformedof single layerof stratifiedsquamousepithelium
 It protectsthe cornea.
II. Middle vascular layer:
It consistsof followingparts:
1. Choroid:
 It isthick vascularandpigmentedlayersituatedbelow sclera.
 The pigmentedcellsabsorbslightandpreventitfrombeingreflected.
 The functionof choroidisto provide nutritionandtopreventreflectionof light.
2. Ciliarybody:
 These are attachedto choroidand presentatthe junctionof scleraandcornea.
 It consistsof twosetsof ciliarymuscle andsuspensoryligament.
 Ciliarybodyisattachedto lensandholdsitinposition
 Its functionistochange the shape of lensbycontractionor relaxationof muscle
3. Iris:
 It ismuscular,pigmentedandopaque diaphragmwhichhangsinthe eye ball infrontof lens.
 It has small circularopeningcalledpupil.

3.  It has twotypesof muscles;circularand radial muscle.The movement of these musclescontrol
the size of pupil.
 Pigmentinirisgivescolortoeye.
 Iriscontrol the amountof lightenteringintoeye bycontrollingthe size of pupil.
III. Inner layer:
It consistsof photoreceptorcellsandphotosensitive elements.
1. Retina:
 Retinaisinnermostlayer.
 Neuroretinacontainshighlyspecializedphotoreceptornerve cells;rodsandcones
 Each eye ball has 125 millionsof rodcellsand7 millionsof cone cells.
 Small depressioninretinal walliscalledFoveacentraliswhich containsonlycone cells.
 Foveacentralisishighlysensitive tolightandformsmagnifiedimage andgive sharpandacute
vision.
 The optic nerve enterretinaata pointcalledblindspot.Itdoesnotcontainsanyrods or cone
cells.Itisleastsensitivetolightandformsno image whenlightfallsonblindspot
Rod cell:
 rods are sensorsforperceptionof blacktowhite shades
 Nightvisionisalmostrodvision.
 It functionindimlight
 Containsa photosensitive pigmentrhodopsinformedfromvitaminA.
Cone cell:
 Conesare sensorsforperceptionof colors.
 It functionsinbrightlightanddifferentiate colors.
 Containsa photosensitive pigmentiodopsin.
Eye lensand chambers
1. Eye Lens:
 It isa large,flexible,transparentbiconvex andfibrouscrystalline bodysituatedbehindiris.
 Lensis enclosedinatransparentelasticcapsule.
 Ciliarymusclescontrol the thicknessof lensanditspowerof accommodation.
 It formsthe image of the objectonretina.

4.  Lensseparatesthe eye ball intotwochamber
i.Aqueous chamber
ii.Vitreouschamber
Aqueouschamber:
 It isa smallerfluidfilledchamberbetweencorneaandlens.
 It isfilledwithaqueoushumourcontainingaminoacids,glucose,ascorbicacid,hyaluronicacid
and respiratorygases.
 The aqueoushumournourishes the lensandcorneaandrefractslightraysto focus onretina.
Vitreouschamber:
 It isa largerfluidfilledchamberbetweenlensandretina.
 It isfilledwithgelatinousvitreoushumourcontainingsaltsandmucoproteins
 It supportsretinaandrefractslightto focuson retina.