Histology of eye

1. Eye Histology
Assoc. Prof. Dr. Karim Al-Jashamy
IMS/MSU 2010

2. -Thesuperiorandinferiortarsal
platesaredensefibrousplates
thatgivesupportandformtothe
eyelids.Tarsalglandsproduceoily
secretionstopreventtearsfrom
leakingout,whiletheeyelidsstay
dry.
-Theobicularisoculimuscle
containsbothpalpebralandorbital
partsandactstoclosetheeyelids.
-Thelevatorpalpebraesuperioris
muscleelevatestheuppereyelid.
Itisaskeletalmuscleunder
voluntarycontrol.

3. The eye
•Acomplexandhighlydeveloped
photosensitiveorganthatpermitsan
accurateanalysisoftheform,light
intensity,andcolorreflectedfrom
objects.
•Eacheyeiscomposedofthree
concentriclayers:anexternallayer
thatconsistsofthescleraandthe
cornea;amiddlelayeralsocalledthe
vascularlayerconsistingofthe
choroid,ciliarybody,andiris;andan
innerlayerofnervetissue,theretina,
whichconsistsofanouterpigment
epitheliumandaninnerretina
proper.
•Thephotosensitiveretinaproperis
partofthecentralnervoussystem
and communicates withthe
cerebrumthroughtheopticnerve
andextendsforwardtotheora
serrata.

4. Diagram, showing the structure of the eye, retina, fovea, and ciliary body.
An enlarged diagram of the fovea is shown at the lower right: (1) axons of
ganglion cells; (2) bipolar cells; (3) rods; (4) cones. Enlarged diagrams of the
ciliary body (upper right) and retina (lower left)

5. •Thescleraconsistsoftough,
denseconnectivetissuemadeup
mainlyofflatcollagenbundles
intersectinginvariousdirectionswhile
remainingparalleltothesurfaceofthe
organ,amoderateamountofground
substance,andafewfibroblasts.
•Theexternalsurfaceofthesclerathe
episcleraisconnectedbyaloose
systemofthincollagenfiberstoadense
layerofconnectivetissuecalled
Tenon'scapsule.Tenon'scapsule
comesintocontactwiththeloose
conjunctivalstromaatthejunctionofthe
corneawiththesclera.
•Betweenthescleraandthechoroidis
thesuprachoroidallamina,athinlayer
oflooseconnectivetissuerichin
melanocytes,fibroblasts,andelastic
fibers.
Sectionofchoroidandsclera.Thechoroidisa
highlyvascularlayer(arrowheads)of
connectivetissuecontainingmelanocytesthat
preventthereflectionofincidentlight.
Thescleraisadenselayerofconnective
tissuerichinfibersofcollagentypeI,
arrangedinparallelbundles.

6. •The outer layer, or sclera,
consists of dense fibrous
connective tissue.
–The sclerais "white" of the eye.
–The sclerais continuous with the
transparent substantiapropriaof the
cornea.
–The exposed front surface of the eye,
including the cornea, is also covered
by a thin, non-keratinized stratified
squamousepithelium.
1 -cornea
2 -iris
3 -posterior chamber of the eye
4 -lens
5 -vitreous body
6 -ciliary body
7 -retina
8 -choroid
9 -sclera
10 -canal of Sclemm
11 -growth area of the lens
12 -anterior epithelium of the lens

7. RETINA, CHOROID
•1 -8 -retina
1 -optic nerve fibers
2 -ganglion cell layer
3 -inner plexiform
layer
4 -inner nuclear layer
5 -outer plexiform
layer
6 -outer nuclear layer
7 -outer processes of
rods and cones
8 -pigmented
epithelium
9 -choroid
10 -sclera

9. •Cornea
•colorlessandtransparent.
•Atransversesectionofthecornea
showsthatitconsistsoffivelayers:
epithelium,Bowman's membrane,
stroma,Descemet'smembrane,and
endothelium.
•Thecornealepitheliumisstratified,
squamous,andnonkeratinizedand
consistsoffiveorsixlayersofcells.
•Inthebasalpartoftheepitheliumare
numerousmitoticfiguresthatare
responsibleforthecornea'sremarkable
regenerativecapacity
•Thesurfacecornealcellsshow
microvilliprotrudingintothespace
filledbytheprecornealtearfilm.
•Thisepithelialtissueiscoveredbya
protectivelayeroflipidand
glycoprotein,about7mthick.The
corneahasoneoftherichestsensory
nervesuppliesofanyeyetissue.

10. CORNEA
•1 -anterior epithelium
(stratified squamous
epithelium)
2 -anterior basement
(Bowman's) membrane
3 -substantiapropria
4 -posterior basement
(Descemet's)
membrane
5 -posterior epithelium
(simple squamousor
endothelium)

11. •Thislayer,Bowman'smembrane,consistsofcollagenfiberscrossingatrandom,
acondensationoftheintercellularsubstance,andnocells.Bowman'smembrane
contributesgreatlytothestabilityandstrengthofthecornea.
•Thestromaisformedofmanylayersofparallelcollagenbundlesthatcrossat
approximatelyrightanglestoeachother.Thecollagenfibrilswithineachlamella
areparalleltoeachotherandrunthefullwidthofthecornea.Betweentheseveral
layers,thecytoplasmicextensionsoffibroblastsareflattenedlikethewingsofa
butterfly.
•Descemet'smembraneisathickhomogeneousstructurecomposedoffine
collagenousfilamentsorganizedinathree-dimensionalnetwork.
•Theendotheliumofthecorneaisasimplesquamousepithelium.Thesecells
possessorganellesforsecretionthatarecharacteristicofcellsengagedinactive
transportandproteinsynthesisandthatmayberelatedtothesynthesisand
maintenanceofDescemet'smembrane.
•Thecornealendotheliumandepitheliumareresponsibleformaintainingthe
transparencyofthecornea.Bothlayersarecapableoftransportingsodiumions
towardtheirapicalsurfaces.Chlorideionsandwaterfollowpassively,maintaining
thecornealstromainarelativelydehydratedstate.Thisstate,alongwiththe
regularorientationoftheverythincollagenfibrilsofthestroma,accountsforthe
transparencyofthecornea.

12. •Thecorneoscleraljunction,orlimbus,isanareaoftransitionfrom
thetransparentcollagenbundlesofthecorneatothewhiteopaque
fibersofthesclera.Itishighlyvascularized,anditsbloodvessels
assumeanimportantroleincornealinflammatoryprocesses.
•Thecornea,anavascularstructure,receivesitsmetabolitesby
diffusionfromadjacentvesselsandfromthefluidoftheanterior
chamberoftheeye.
•Intheregionofthelimbusinthestromallayer,irregularendothelium-
linedchannels,thetrabecularmeshwork,mergetoformSchlemm's
canal,whichdrainsfluidfromtheanteriorchamberoftheeye.
Schlemm'scanalcommunicatesexternallywiththevenoussystem.
•Middle,orVascular,Layer
•Themiddle(vascular)layeroftheeyeconsistsofthreeparts:choroid,
ciliarybody,andiris,knowncollectivelyastheuvealtract.

13. -Theciliarybodycontainsciliarymusclethatiscomposedofsmoothmuscle.Contraction
andrelaxationoftheciliarymuscleschangethetensionofthezonularfibers,orsuspensory
ligaments,ofthelens.Thisallowsthelenstochangeshape,aprocessknownas
accommodation.
-Theciliaryprocessesarefoldsofconnectivetissuethatarecoveredbytwolayersof
epithelium.Thereisalsoacomplexvasculaturethatcannotbeseeneasily.Fluidfromthese
vesselsisprocessedandtransportedbytheepithelialcellstotheposteriorchamberas
aqueoushumor.Theepithelialcellsconstitutetheblood-aqueousbarrier.
-

14. -Theaqueoushumorenterstheanterior
chamberthroughthepupilasitflows
betweenthelensandtheiris.
-Aqueoushumorleavestheanterior
chamberthroughthetrabecular
meshworkandintothecanalof
Schlemm.
-Thisisanendotheliallines,
circumferentiallyarrangedvesselthat
communicateswithveinsinthesclera
andreturnstheaqueoushumorbackto
thegeneralcirculation.
-Obstructionofthetrabecularmeshwork
andcanalsofSchlemmarethoughtto
bethemajorcauseofelevated
intraocularpressure,whichcouldthen
leadtoglaucoma.

15. -The irisis detailed here in higher magnification. Note
the anterior and posterior chambers to help orient
yourself.
-The anterior surface of the iris contains loose, variably
pigmented stroma. It is open to the circulating aqueous
humor within the anterior chamber.
-Two layers of heavily pigmented epithelium cover the
posterior surface of the iris.
-Note that the sphincter pupillae muscle can be easily
seen near the pupil margin. It is smooth muscle
controlled by parasympathetics. The dilator pupillae
muscle is more difficult to identify, but it dilates the pupil
upon sympathetic innervation.

16. Lens
•The lens consists of a
lens capsule, the
subcapsular epithelium
and lens fibres. It does
not contain blood
vessels or nerves.