Sclera (post 5/6)

Overview of Eye Histology 

Tunica fibrosa (fibrous, supporting layer) 

Cornea (ant 1/6); Sclera (post 5/6) 

Tunica vasculosa (uvea) (vascular layer) 

Ciliary body, Iris, Choroid 

Tunica interna (retina) (retinal, neural layer) 

Neural retina; Retinal pigment epithelium 

Pars optica: ora serrata 

Pars ciliaries reinae; Pars iridica retinae 

Histo: Eye Ear - 

1

Cornea 


2

Cornea: transparent, avascular, 

refractive index = 1.376 

Corneal epithelium: 

noncornified, stra. Squ. Epi.; 

thin basal lamina; nuclear 

DNA-ferritin for UV protection 

Bowman’s membrane: 

collagen fibril; acellular 

Substantia propria (stroma): 

transparency, collagen fibrils in 

orthogonal array, fibroblast 

(CF), cornal proteoglycans 

Descemet’s membrane: thick 

basal lamina of endothelium 

Endothelium: simple squ.; 

metabolic exchange; limited 

proliferation 


3

Sclera (S); Choroid (C); Retina (R) 


4

Sclera: dense fibroelastic tissue; 

fibers parallel to eye surface 

Episcleral tissue - loose vascular c.t. + conjunctiva 

Sclera proper - dense network of collagen fibers 

Suprachoroid lamina (fusca) - thin transitional layer to 

choroid; elastic fibers, pigment cells 

Sclera 


5

1. Bruch’s membrane (lamina vitrea)- basement mem. of 

pigment epi. (retina) 

2. Choroid capillaries layer 

3. Vascular layer (contains pigment cells and vessels) 

4. Suprachoroid layer – collagen and elastic ff. & pigment 

cells (melanoytes) 

choroid 

2008/01/02 Eye & Ear 

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6

Ciliary body and iridocorneal angle 

Ciliary body: forward continuation of choroid, 

highly vascular, with abundant melanins 

Ciliary (smooth) muscles of 3 functional groups: 

meridional (longiudinal), radial (oblique), 

circular (sphincteric) 


7

Ciliary process 

Branching epithelial folds with c.t. 

core (C), fenestrated capillaries, 

producing 

aqueous humor: refractive 

index of 1.33 

Double cuboid epi. (E) 

Non-pigmented: superficial 

Pigmented: deep 

Suspensory ligaments (S, ciliary 

zonule) 

M: smooth muscles of ciliary body; 

PC: posterior chamber 


8

Iris 

Anterior (facing cornea): fibroblast & stromal melanocyte; 

endothelium (in fetus) 

General stroma: loose, highly vascular c.t., chromophores; smooth 

muscles (sphincter & dilator pupillae) 

Posterior (facing lens): 2 layers of pigment epithelium continuous 

from ciliary process (ant. pig. epi.; post. pig. epi.); myoepithelial cell, 

(dilator pupillae) 


9

Circulation of Aqueous humor 

Ciliary process: production 

Posterior chamber 

Anterior chamber 

collagenous endothelium-lined 

Trabecular meshwork (T; space 

of Fontana): endothelium-lined 

Canal of Schlemm (CS): 

endothelium-lined 

Episcleral venous system in 

sclera 

Glaucoma: Increased 

intraocular pressure (IOP) 

I: root of iris; C: cornea 


10

Retinal organization: photoreceptors, 

interneurons, retinal ganglia neurons, 

retinal pigment epithelium 

10: inner limiting mem.: basal lamina 

of Muller cells 

9: optic nerve fiber: axons of retina 

ganglia neurons 

8: ganglia cell layer: cell bodies of 

retina ganglia neurons 

7: inner plexiform layer: synaptic 

connections between dendrites of 

retina ganglia neurons and axons of 

bipolar neurons 

6: inner nuclear layer: nuclei of 

interneurons (horizontal, amarcrine, 

bipolar et al.) and Muller cells 

Muller cell 


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Retinal organization: photoreceptors, 

interneurons, retinal ganglia neurons, 

retinal pigment epithelium 

5: outer plexiform layer: processes 

of photoreceptors and interneurons 

4: outer nuclear layer: nuclei of 

photoreceptors 

3: outer limiting mem.: zonulae 

adherentes between Muller cells 

2: photoreceptor layer: rods and 

cones with organelles 

1: retina pigment epithelium: 

junctional complexes and gap 

junctions on Bruch’s mem. of 

choroid; blood-retina barrier 

Muller cell 


12

Retina: Muller cell (glia) 

inner limiting mem. 

outer limiting mem. 


13

Photoreceptor: rod, cone 

Rod for low light intensity; 

cone for color, high light 

intensity 

Outer segment: 

photoreceptor proper 

Connecting stalk: cilium 

(9 microtubule doublets), 

calyceal process 

Inner segment: with 

organelles, microtubules 

outer (ellipsoid): 

mitochondria 

inner (myoid): Golgi, 

rER, free ribosomes 

calyceal process 

M: outer limiting mem.; P: pigment epi. 

B: Bruch’s mem. 


14

od 

Discs in rods and cones 

regularly spaced horizontal discs from transverse infoldings of plasma 

membranes in outer segment near cilium 

shed and phagocytosed by retina pigment epithelium (phagosome) 

cone 

cone 

rod 


15

Retina pigment epithelium: basally-located nucleus; 

mitochondria, melanin granule; microvilli 


16

Optic disc (optic papilla) 

Optic nerve: axons of 

retina ganglia neurons 

accompanying central 

retinal artery and vein 

no photoreceptors in 

optic disc (blind spot) 

Traversing sclera (lamina 

cribrosa, cribriform plate) 

Sclera: equivalent to 

dura 

Uvea tract: equivalent 

to pia-arachnoid 

Optic papilla (optic disc; blind spot) 


17

Fovea centralis (FC) 

retina of conical depression; 

4 mm lateral to optic disc; 

surrounded by 1 mm-wide 

macula lutea 

only closely packed cones 

(100,000 cones); 1-to-1 ratio 

of cones to bipolar neurons 

maximal photosensitivity: on 

the visual axis with least 

refractory distortion; reduced 

inner layers of retina; 

absence of retina vessels 

Macular degeneration: loss 

of visual acuity 


18

Lens 

Lens capsule: basal lamina, produced by anterior lens cells (type IV 

collagen, proteoglycans); connected to suspensory lig. 

Subcapsular epithelium: a cuboid layer, only on anterior surface of 

lens; with gap junctions 

Lens fibers: derived from subcapsular epithelium 

lose nuclei & organelles; filled with crystalins 

Refractive index of 1.38~1.5 


19

Vitreous body 

Homogenous gel: 

99% water (vitreous humor) 

bound to hyaliuronic acid 

some hyalocytes (round or 

fusiform) for collagen, 

glycosaminolycans 

(hyaluronan) 

Colorless, refractive index of 

1.334 

Hyaloid (Cloquet’s) canal: 

remnant of hyaloid artery (at 

center of vitreous body from 

optic disc to post. lens capsule) 


20

tarsal plate: dense c.t.; 

superior tarsal muscle of 

Muller 

tarsal sebaceous 

(Meibomian) gland: 25 

(upper), 20 (lower); oily 

layer on tear film 

accessory lacrimal gland 

of Wolfring 

apocrine glands of 

eyelashes (glands of Moll) 

all gland secretion: 

synchronized with lacrimal 

glands via vasoactive 

intestinal peptide (VIP) 

Eyelid: hairy skin + orbicularis 

oculi + palpebral conjunctiva 


21

Eyelid, Tarsal plate, Meibomian gland: Histology 


22

Conjunctiva 

Stratified columnar epi., goblet cells 

Loose vascularized c.t. 

(melanocyte at basal layer) 


23

compound tubulo-acinar 

serous gland 

similar to parotid gland 

tear film: proteins (tear 

albumins, lactoferrin), 

enzymes (lysozyme), lipids, 

metabolites, electrolytes, 

drugs during therapy 

Lacrimal glands 


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Review: Eye 

Histological and Gross 

correlations: tunica 

fibrosa: cornea, sclera 

vasculosa: choroid, ciliary, 

iris 

neural retina, retina 

pigment epithelium (RPE) 

Retina 

Cells: photoreceptors, 

neurons (ganglia, 

interneurons), retina 

pigment epithelium, Muller 

cell 

Organization: 10 layers 

Optic disc, Fovea 

Glands: lacrimal, tarsal 

Muller cell 


25

Ear 

Ext. ear: ext. acoustic meatus 

Mid. ear: auditary ossicles, Eustachian 

(auditory) tube 

Inn. ear: cochlear, vestibular apparatus 


26

TM: tympanic mem. 

LSC: lateral 

semicircular canal 

AC: mastoid air 

cells 

V: vestibule 

C: cochlea 

arrowhead: oval 

window 


27

External acoustic meatus (Skin) 

Cartilage (ext. 3/1) and inside temporal bone (inner 2/3) 

Hair follicles (F), Sebaceous gland, Ceruminous (apocrine) gland 


28

Tympanic membrane 

Outer: stratified squamous epi. (SSE) 

Connective tissue (CT) 

Inner: simple cuboid epi. (SCE) 


29

Eustachian (auditory) tube: bony and cartilaginous parts 

Simple columnar epi. near tympanic cavity 

Pseudostratified columnar epi. with goblet cells near pharynx 

Submucosa: mixed galnds 


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Inner ear: Labyrinth 

Bony labyrinth 

Vestibule, Cochlea 

Membranous labyrinth: with 

endolymph inside (perilymph 

outside) 

Vestibular labyrinth (Utricle, 

Saccule, Semicircular duct) 

Cochlear duct 


31

Sensory organs of 

Vestibular mem. labyrinth 

Mucula in Utricle and Saccule 

Hair cells: Single kinocilium; 

bundle of stereocilia 

type I (goblet) 

type II (columnar) 

Supportive cells 

Otolith membrane (otoliths): 

otoconia 

Crista amuplualris in ampular 

parts of semicircular ducts 

Hair cells (type I goblet & type 

II columnar), Supportive cells 

Cupula: without otoliths 


32

Macula: overview 


33

Macula: Histology 

Hair cells: type I (goblet); 

type II (columnar) 

Kinocilium; Stereocilia 

Supportive cells 

Otoliths 


34

Crista ampularis in 

Semicircular duct 

Hair cells 

Type I; Type II 

Cupula: gelatinous proteinpolysaccharide 

complex 

No otoliths 

exposed to endolymph 


35

Crista ampularis 

(CA): Histology 

Cu: cupula 

EP: epithelium 

HC: hair cell 

SC: 

supportive cell 

CT: 

connective 

tissue 


36

Vestibular sensory 

hair cells 

Hair cells as 

mechanoelectric 

transducer 

Kinocilium with basal 

body 

Steroecila (hair bundle) 

Actin filaments 

Cross-linked by fimbrin 

and espin (actinbundling 

proteins) 

anchored to terminal 

web (cuticular plate) 


37

Plaque 

Kinocilium and Stereocilia 

Mechanoelectric transducer 

channel protein at tip of plasma 

membrane of stereocilia 

(electron-dense plaque) 

tip link: tip of stereocilium with 

adjacent shaft of longer 

stereocilium (transduction K + 

channels are located) 

Kinocilium: cilium (microtubules) 

Stereocilia: microfilaments 

(actins) 


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Tip link in Stereocilia 

Tip link: mechanoelectric 

transduction (MET) channel 

proteins at the tip of 

stereocilium associated with 

adjacent shaft of longer 

stereocilium (transduction 

K + channels are located) 

Activated by deflection 

toward kinocolium, influx of 

K + (endolymph: rich in K + ); 

activation of Ca ++ channels 

to release neurotransmitters 


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Mechanoelectric transduction: 

Displacement of stereocilia and 

Activation of vestibular sensory neurons 


40

Cochlea and cochlear 

duct (labyrinth) 

Cochlea (bony labyrinth): 2 and ¾ 

turns 

Modiolus (central axis) 

Helicotrema 

Cochlear duct (mem. labyrinth) 

Scala vestibule (SV): perilymph 

Vestibular membrane 

(Reissner’s membrane) 

Scala media (SM, cochlear 

duct): endolymph 

Basilar membrane 

Scala typamni (ST): perilymph 

Spiral ganglia (SG) 

Frequency-position: Low in 

apex; High in basal turn 


41

Vestibular (Resissner’s) membrane: EM 

Mesothelium: facing peilymph of 

scala vestibular 

Epithelium facing endolymph of 

scala media 


42

Osseous spiral lamina (O) 

Spiral limbus (SL) 

Spiral ganglia (G), nerve (N) 

Endolymph 

Organ of Corti on 

Basilar membrane (BM) 

Stria vascularis (SVasc) 

Spiral igaments (SLig) on 

endosteum 


43

Organ of Corti: Sensory organ of cochlear duct (labyrinth) 

Hair cells: Inner (close to spiral lamina): single row; Outer (farther 

from spiral lamina): 3 ranks in basal coil; 5 ranks in apex 

Tectorial mem.: from spiral limbus to organ of Corti by stereocilia 

of hair cells; radially oriented bundles of collagens embedded in 

glycoprotein matrix 

Phalangeal (supporing) cells: inner and outer; Pillar cells et al. 


44

Hair cells of organ of Corti 

Stereocilia in hair cells of 

organ of Corti; 

1 inner row; 3 outer rows 

Apical cuticular plate (ACP) 

of phalangeal cells 


45

Organ of Corti: hair cells 

Hair bundle (stereocilia) 

No cilium (kinocilium), basal body retains 

Inner hair cell Outer hair cell 


46

Sound perception: 

mechanoelectric transduction 

sound wave → stapes → oval 

window → scala vestibuli → 

scala media → basilar mem. 

(organ of Corti, stereocilia of 

hair cells) and tectorial mem. 

scala tympani → round window 


47

Membranous labyrinth 


48

Vestibule 

Utricle 

Macula 

Otolith mem 

(otoconia) 

Linear movements 

Saccule 

Macula 

Otolith mem 

(otoconia) 

Semicircular duct 

Crista ampularis 

Cupula 

Angular movements 

Vestibular ganglia (of Scarpa), near int. acoustic meatus 

Review: Membranous 

labyrinths 

Cochlea 

Cochlear duct 

Organ of Corti 

Tectorial membrane 

Sound perception 

Spiral ganglia, modiolus 


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Sclera (post 5/6)

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