HistologyoftheEye

Colorindex:Slides..Important..Notes..Extra..

Objectives:Bytheendofthislecture,thestudentshouldbeabletodescribe:

üThegeneralstructureoftheeye.üThemicroscopicstructure of:

Cornea.Retina.Limbus.

Threecoats(3Tunics) Components Notes

1- Fibroustunic: A- CorneaB- Sclera

Outermostandtoughcoat

2- Vascular tunic:A- Choroid

B- CiliarybodyC- Iris.

- Themiddlecoat.- Alsocalleduveal

coat.

3- Neuraltunic: A- Retina Innermostandnervouscoat

EYEBULB

Cornea: Itisthetransparent,avascular andhighlyinnervatedanteriorportionofthefibrouscoat.(Represent theanterior1/6oftheouterfibrouscoatofeyeblub)(Ittakesitsnutrientsfromlimbusviadiffusion )

Composedof5distinctlayers:

1.Cornealepithelium.2.Bowman’smembrane.3.Stroma.4.Descemet’smembrane.5.Cornealendothelium.

1- Cornealepithelium:

Non-keratinizedStratifiedsquamousepithelium.(itisanterior)Containsnumerousfreenerveendings.

2- Bowman’smembrane:

Itisahomogenousnon-cellularlayercontainingtypeIcollagenfibrils. (posteriortotheepithelium)

3- Stroma:

Itisthethickestlayer(about90%).ItiscomposedofparallellamellaeofdensecollagenousC.T.EachlamellaiscomposedmainlyofparalleltypeIcollagenfibers withlongfibroblasts.

4- Descemet’smembrane: Itisathickbasementmembrane.(Anteriortotheendothelium)

5- Cornealendothelium:

- Itissimplesquamousepithelium. (posterior)- Functions:1- FormationofDescemet’smembrane.2- Keepingthestromarelativelydehydrated(sod.pump→waterwithdrawalfromthestroma).

Fibroustunic:CORNEAمھم

LIMBUSمھم (CORNEOSCLERALJUNCTION)

- Itisthetransitionregionbetweenthecorneaandsclera.- Itisabout1.5mmwidth.- Itishighlyvascular.Itgivesnutrientstocornea.

- Itcontains:1- Trabecularmeshwork(smallwindows):Endothelium-linedspaces.ItleadstocanalofSchlemm.(AlsocalledspacesofFontana)

2- CanalofSchlemm:Itdrains theaqueoushumorintothevenoussystem.Thecanalmimicsbloodcapillaries.(Ifthereisanyobstructioninthepathwayofaqueoushumoritwillleadtoglaucoma)

Sclera

Cornea

Iris

Ciliarybody

Canal of Schlemm

Fibroustunic:Sclera• Itcovers theposterior 5/6ofthefibrous

tunic.• ScleraProper:consistsofinterlacing

bundlesoftypeIcollagen(densecollagenousC.T.,irregulartype).

• Melanocytes arelocatedinthedeeperregions.

Vasculartunic:Choroid• isthevascular,pigmentedposteriorto

cornea portionofthemiddlevasculartunic.

• Structure:1. ItiscomposedmainlyoflooseC.T. with

melanocytes.LooseCTisalwaysrichinbloodvessels2. Itisseparatedfromtheretinabyits

Bruch’smembrane.

Bruche’s membraine

Vasculartunic:CiliarybodyItistheanteriorcontinuationofthechoroid.Itsurroundsthelens.Structure:• ItisformedofloosevascularandpigmentedC.T.

thatcontains3bundlesofsmoothmusclecells(ciliarymuscle).

• Itsinnersurfaceislinedbyparsciliaris retinae(2rowsofcolumnarcells;outerpigmentedandinnernon- pigmentedlayers).• Itsinnersurfaceishighlyfoldedformingthe

ciliaryprocesses.

Ciliaryprocesses(smoothmuscles)

• Processesprojectfromtheinnersurfaceoftheanterior1/3oftheciliarybodytowardsthelens.

• Arecoveredbyparsciliaris retinae(2rowsofcolumnarcells).

• Theygiveattachmenttothelenssuspensoryligaments(zonule fibers).

• ciliaryprocessiswhatcontrolscurvatureofthelensbutitisnotdirectlyattachedtoit.

Posteriorchamber

Anteriorchamber

1- Anteriorborderlayer Incompletelayeroffibroblastsandmelanocytes.Most ofitareconessells

2- Stroma PoorlyvascularizedC.T.withfibroblastsandmelanocytes.

3- VessellayerMoreprominentlayer

Well-vascularizedlooseC.T.Centrally,itcontainscircularly arrangedsmoothmusclefibers(sphincterpupillaemuscle).

4- DilatorpupillaemusclelayerArranged insunraysshape

Containsradiallyarrangedmyoepithelialcells.Sotheirisconstrictsanddilatesthepupil.

5- Posteriorsurfacelayer(pigmentedepitheliumlayer)

Itiscomposedof2rowsofpigmentedepithelialcells(parsiridisretinae).Theyarethecontinuationofparsciliarisretinae.

IRIS

Layers Features Function

1-Pigmentedepithelium

ü Cuboidaltocolumnarcells (singlelayer). Short columnü Apicalmicrovilli. Increase surfaceareaandactasphagocyteü Abundanceofmelaningranules.

ü Absorblight.ü Phagocytosisofmembranousdiscsfromtipsof

rods.(Whenrodsarestimulated,theyrupture)ü EsterificationofVitaminA(inSER).

2-Rodsandconeslayer.

ü Arephotoreceptorcells.ü Eachhas:1.Dendriteformedof:- Outersegment(OS): containsmembranousdiscscontainingrhodopsin(inrods)andiodopsin (incones).- ConnectingStalk: withmodifiedcilium.- Innersegment(IS).2.Cellbody.3.Axon: synapseswithdendriteofbipolarneuronofinnernuclearlayer.

ü Rodsarereceptorsfordimlight(lowintensitylight).

ü Conesarereceptorsforbrightlightandcolorvision (red,green &blue).

3-Outerlimitingmembrane. Aregionofzonulae adherentsjunctionsbetween Mullercellsandthephotoreceptors.

4-Outernuclearlayer: Containsnucleioftherods&cones.

5-Outerplexiform layer: Containsaxodendritic synapsesbetweenthephotoreceptorcellsanddendritesofbipolarandhorizontalcells.

6-Innernuclearlayer:

Containsthenuclei of:1- Bipolarneurons.2- Horizontalneurons.3- Amacrine neurons(unipolar neurons):4- Neuroglialcells(Mullercells)thatextend betweenthevitreousbodyandtheinnersegmentsofrodsandcones.

7-Innerplexiform layer: Containsaxodendritic synapsesbetweenaxonsofbipolarneuronsanddendritesofganglioncellsandamacrine cells.

8-Ganglioncelllayer: Containscellbodiesoflargemultipolar neuronsoftheganglioncells.

9-Opticnervefiberlayer: Containsunmyelinated axonsoftheganglion cells.N.B.Theseaxonsbecomemyelinated asthenervepiercesthesclera.

10-Theinnerlimitingmembrane: Itisformedbythebasallaminae oftheMullercells.

light

Cones>Color >Large>BrightLight

RETINAمھم

Theaxonsofrodsandconessynapsewithdendritesofinnernuclearlayer.Theinnernuclearlayercellsynapsewitheachotherandwithganglioncelllayer.

differentlayersoftheretina

RETINA(mainstructure)

Lastlayerisreceptorsandfirstisopticnerveaxons

1- Pigmentedepithelium.

2- Nervecells:

- Photoreceptorcells(rods&cones).

- Bipolarneurons.

- Ganglioncells.

- Associationneurons:

i.Horizontalcells.

ii.Amacrine cells.

3- Neuroglial cells:

- Muller’scells.

- Astrocytes.scattered

Itliesinthecenterofmaculalutea.

Cones arehighlyconcentratedinthefovea.

Itisresponsibleforvisualacuity.

Foveacentralis: Typesofcellsintheretina: Definition L.M.Picture

Itisthetransparentmucousmembraneliningtheinnersurfacesofthe

eyelids(palpebralconjunctiva)andreflectingontothescleraoftheanteriorsurfaceoftheeye

(bulbarconjunctiva).

1- Epithelium:Stratifiedcolumnarepitheliumwithnumerousgoblet

cells.

2- Laminapropria:LooseC.T.

Lessthicknessdepressioncalledmaculaluteaneartheopticnerve

RETINAمھم CONJUCTIVA

MCQ’s1-C2-B3-D4-B5-B6-D7-C8-A

1-whichoneofthefollowingstructureskeepthestromaofcornearelativelydehydrated?A-CornealepitheliumB-Bowman’smembraneC-CornealendotheliumD-Descemet’smembrane

2-Canalofschlemm isfoundinwhichofthefollowing?A-RetinaB-limbus(Corneoscleraljunction)C-scleraD-Choroid

3- whichofthefollowingasthefunctionofthepigmentedepithelialcellsfoundinretina?A- AbsorblightB- PhagocytosingoftipsoftherodetoregenerateC- EsterificationofVit AD- Allabove

4- whichofthefollowingsitescontainthehighestconcentrationofcones?A- OpticdiskB- FoveacentralisC- ConjunctivaD- Allabove

5-ThescleraconsistoflosecollagenousC.TregulartypeA-trueB-false

6-ThechoroidisseparatedfromtheretinabyA-Bowman’smembraneB-CanalofschelmmC-opticdickD-Bruch’smembrane

7-Whichlayershavethenucleiofrodsandcons?A-RodandConslayerB-innernuclearlayerC-OuternuclearlayerD-Ganglioncelllayer

8-Gobletcellsfoundarein?A-conjunctivaB-RetinaC-ChoroidD-limbus

Thankyou&goodluck- Histologyteam

Doneby:ü AhmedBadahdahü Mutasem Alhasaniü OmarTurkistaniü Nawaf Aldarweeshü MohammedKhojah

Teamleaders:ü RanaBarasainü FaisalAlrabaii

References:ü Females’andMales’slides.ü Doctors’notes