Eye and Ear Histology

OutlineI. Eye histology

A. Layers of eyeball1. Sclerocorneal layer2. Uvea3. Retina

B. Aqueous humor production and flowC. Eyelid, conjunctiva, lacrimal gland

II. Ear histology (Inner ear)A. Bony labyrinth

1. Vestibule2. Semi-circular canal3. Cochlea

B. Membranous labyrinth1. Utricle and saccule2. Membranous labyrinth3. Membranou coclea



















Layers of the eyeball

Layers of the eyeball

Layers of the eyeballCorneoscleral coat, including sclera and

cornea1


cornea1


cornea1

Uvea: a vascular layer including choroid, ciliary

body and iris

2


cornea1


body and iris

2


cornea1


body and iris

2

Retina, including outer pigment epithelium, inner

neural retina, and epithelium of ciliary body

and iris

3


cornea1


body and iris

2

Retina, including outer pigment epithelium, inner

neural retina, and epithelium ciliary body

and iris

3

Sclera consists of dense, irregular connective tissue, making it opaque

Corneoscleral coat, including sclera and cornea1

Cornea covers the anterior one sixth of the eye, and is continuous with the fibrous sclera posteriorly. 5 layers:



Cornea covers the anterior one sixth of the eye, and is continuous with the fibrous sclera posteriorly. 5 layers: 1. Stratified squamous, non keratinizing corneal epithelium



Cornea covers the anterior one sixth of the eye, and is continuous with the fibrous sclera posteriorly. 5 layers: 1. Stratified squamous, non keratinizing corneal epithelium 2. Bowman’s membrane



Cornea covers the anterior one sixth of the eye, and is continuous with the fibrous sclera posteriorly. 5 layers: 1. Stratified squamous, non keratinizing corneal epithelium 2. Bowman’s membrane 3.Corneal stroma (substantia propria)



Cornea covers the anterior one sixth of the eye, and is continuous with the fibrous sclera posteriorly. 5 layers: 1. Stratified squamous, non keratinizing corneal epithelium 2. Bowman’s membrane 3.Corneal stroma (substantia propria) 4. Descemet’s membrane



Cornea covers the anterior one sixth of the eye, and is continuous with the fibrous sclera posteriorly. 5 layers: 1. Stratified squamous, non keratinizing corneal epithelium 2. Bowman’s membrane 3.Corneal stroma (substantia propria) 4. Descemet’s membrane 5.Cuboidal cells called the corneal endothelium



A. (E), External stratified squamous epithelium NK 5-6 cells thick(S) Stroma made of 60 layers of long type I collagen fibers arranged in a precise orthogonal array and alternating with flattened cells called keratocytes(EN) Lined internally by endotheliumB. Corneal epithelium rests on Bowman’s membrane (arrow). Stroma is avascular.C. Posterior surface covered by simple squamous epithelium (endothelium) on Descemet’s membrane

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BM

DM

Limbus or corneoscleral junction (CSJ) is where transparent corneal stroma merges with opaque, vascular sclera (S). Stroma of limbus contains scleral venous sinus (SVS), or canal of Schlemm, which receives aqueous humor from anterior chamber (AC).

Uvea: a vascular layer including choroid, ciliary body and iris2

•Consists mainly of choroid•Has a dark brown colour •Melanin pigment, which helps to reduce glare within the eye•Many venous plexuses and capillaries


•Ciliary body extends inwards to form a ring-like thickening•With ciliary processes on its anterior third•Suspensory ligament of the lens (zonular ligament) arises from ciliary process•Ciliary body continues posteriorly until it merges with the retina at ora serrata

This section shows sclera (S) and choroid (C).

Melanocytes are prominent in suprachoroidal lamina (SCL).

Choroid’s inner region, choroidocapillary lamina (CCL), has a rich microvasculature

Between choroid and retina is a thin lBruch’s layer (B).

Outer layer of the retina is the pigmented layer (P)


Iris extends over the anterior surface of the lens from the anterior border of the ciliary body


Consists of 5 layers:



Consists of 5 layers: 1.A discontinuous layer of fibroblasts and melanocytes



Consists of 5 layers: 1.A discontinuous layer of fibroblasts and melanocytes 2.The avascular anterior stromal sheet (lamella)



Consists of 5 layers: 1.A discontinuous layer of fibroblasts and melanocytes 2.The avascular anterior stromal sheet (lamella) 3.A vascular layer of loose connective tissue forming the bulk of the iris



Consists of 5 layers: 1.A discontinuous layer of fibroblasts and melanocytes 2.The avascular anterior stromal sheet (lamella) 3.A vascular layer of loose connective tissue forming the bulk of the iris 4.The posterior membrane, containing the circular sphincter pupillae and radial dilator pupillae muscles



Consists of 5 layers: 1.A discontinuous layer of fibroblasts and melanocytes 2.The avascular anterior stromal sheet (lamella) 3.A vascular layer of loose connective tissue forming the bulk of the iris 4.The posterior membrane, containing the circular sphincter pupillae and radial dilator pupillae muscles 5.A double layer of pigmented epithelium


(A): Central iris, near the pupil (P). Anterior chamber (AC), has no epithelium and consists only of a matted layer of interdigitating fibroblasts and melanocytes. Stroma (S) contains melanocytes. (B): The SEM shows the non—epithelial anterior surface(C): Deep stroma also is richly vascularized (arrowheads). Epithelium on posterior chamber (PC), consists of two layers of cuboidal cells. External pigmented epithelium (PE) are very rich in melanin granules. Dilator pupillae muscle (DPM) . Sphincter pupillae muscle (SPM).

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Retina, including outer pigment epithelium, inner neural retina, and epithelium ciliary body and iris3

Consists of:•Inner, neural retina, containing photoreceptor cells, with a 10 layered structure•Outer retinal pigment epithelium (RPE) that sits on the choroid, consisting of cuboidal melanin-containing cells



Internal (Inner) limiting membrane Composed of the basal lamina of Muller’s cells



Layer of optic nerve fibres Processes of ganglion cells travelling to the brain




Ganglion cell layer Cell bodies of ganglion cells





Inner plexiform layer2nd synaptic layer, between horizontal, amacrine and

bipolar cells and ganglion cells







Inner nuclear layer Cell bodies of horizontal, amacrine, bipolar and

Muller’s cells








Muller’s cells

Outer plexiform layer1st synaptic layer, between photoreceptors and

horizontal, amacrine and bipolar cells








Muller’s cells



Outer nuclear layer Cell bodies of rods and cones








Muller’s cells




External (Outer) limiting membrane Apical boundary of Muller’s cells








Muller’s cells





Layer of rods and cones Inner and outer segments of photoreceptor cells








Muller’s cells





Layer of rods and cones Inner and outer segments of photoreceptor cells

Retinal Pigment Epithelium Melanin containing cells

Fol lowing the path of the l ight, these are:

Inner l imit ing layer (ILL)Ner ve fiber layer (NFL)Gangl ionic layer (GL)Inner plexiform layer (IPL)Inner nuclear layer (INL)Outer plexiform layer (OPL)Outer nuclear layer (ONL)Outer l imit ing layer (OLL)Rod and cone cel l layer (RCL)Pigmented layer (PL)

OPTC NERVE

Openings in

Sclera (Lamina

Cribrosa or

Cribriform

Plate) for Nerve

Fibers from

Retina

Optic

Disc

Choroid

Layer

Retina

Cribriform Plate

Left Eye

Macula & Fovea

Centralis - most acute

vision

Optic Disc

Inferior Temporal Art & Vein

Inferior Nasal Art & Vein

Superior Temporal Art & Vein

Optic Disc

Epithelium of ciliary processes.

Double layer of pigmented (PE) and nonpigmented epithelial (NE) low columnar or cuboidal cells. No true basal lamina is present. Beneath the double epithelium is a core of connective tissue with many small blood vessels (V). Fluid from these vessels is pumped by the epithelial cells out of the ciliary processes as aqueous humor.

Chambers of the eye

There are 3 chambers of the eye:•Anterior chamber, between the cornea and the iris•Posterior chamber, between the posterior surface of the iris and the anterior surface of the lens•Vitreous space, between the posterior surface of the lens and the neural retina.

Unpigmented inner layer of ciliary process

Aqueous humor in posterior chamber



Aqueous humor in anterior chamber

Passes through pupillary aperture



Aqueous humor in anterior chamber

Passes through pupillary aperture

Drains via sclero venous sinus

(Canal of Schlemm)

Transparent, avascular, biconvex structure, suspended by suspensory ligament of the lens

Lens of the eye

3 components:


Lens of the eye

3 components:•Lens capsule, produced by anterior lens cells


Lens of the eye

3 components:•Lens capsule, produced by anterior lens cells•A subcapsular epithelium, a cuboidal layer of cells that is only present on the anterior surface of the lens


Lens of the eye

3 components:•Lens capsule, produced by anterior lens cells•A subcapsular epithelium, a cuboidal layer of cells that is only present on the anterior surface of the lens•Lens fibres derived from the subcapsular epithelial cells


Lens of the eye

Lens capsule (LC) is a thick, homogenous external lamina formed by the epithelial cells and fibers.

Anterior surface of the lens, beneath the capsule, is covered by a simple columnar lens epithelium (LE).

Differentiating lens fibers (DLF) still have their nuclei, but are greatly elongating and filling their cytoplasm with proteins called crystallins.

Mature lens fibers (MLF) have lost their nuclei and become densely packed to produce a unique transparent structure.

Conjunctiva of the eye

•Thin, transparent mucous membrane •Lateral margin of cornea•Across sclera•Covering internal surface of eyelids

•Stratified squamous columnar epithelium, containing many goblet cells, that rests on a lamina propria of loose connective tissue

Eyelid. (a): Skin (S) covering its external surface and smooth conjunctiva (C) lining its inner surface. Hair follicles (F) for the eyelashes. Striated muscle (M) comprising the orbicularis oculi muscle and thick plate of fibroelastic connective tissue tarsus (T). Large sebaceous glands, the tarsal glands (TG) (aka Meibomian glands), with acini secreting into long central ducts (D).

(b): Conjunctiva is a mucous membrane consisting of a stratified columnar epithelium with small and resting on a thin lamina propria (LP). Tarsal gland acini (TG), and the fibrous connective tissue in the tarsus (T) surrounding the acini.

Lacrimal gland.Tubuloalveolar acini (A) Mmyoepithelial cells (M)Blood vessels (V) of the microvasculature and intra— and interlobular ducts (D)

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The inner ear consist of 2 labyrinthine compartments


Bony (osseous) labyrinth, in the petrous portion of the temporal bone

1



1

Membranous labyrinth, within the bony labyrinth

2

Major divisions of the ear- external, middle, and internal regions of the right ear

There are 3 fluid-filled spaces on the inner ear


Endolymphatic spaces, within the membranous labyrinth

1



1

Perilymphatic space, in which the membranous labyrinth is suspended

2



1

Perilymphatic space, in which the membranous labyrinth is suspended

2

Cortilymphatic space, lying within the organ of Corti3



1



1

Vestibule: the central space of the bony labyrinth, containing the utricle and saccule of the membranous labyrinth



1

Semicircular canals extending from the vestibule posteriorly




1

Semicircular canals extending from the vestibule posteriorly

Cochlea, extending from the vestibule anteriorly



Membranous labyrinth, within the bony labyrinth2



Utricle and saccule, contained in the vestibule, and connected by the utriculosaccular duct



Membranous semicircular ducts, within the semicircular canals




Membranous semicircular ducts, within the semicircular canals

Membranous cochlear duct, within the bony cochlea, continuous with the saccule


Bony labyrinth houses a fluid—filled membranous labyrinth. Membranous labyrinth includes organs for sense of equilibrium and balance (the saccule, utricle, and semicircular ducts) and cochlea for the sense of hearing.

(a): Maculae, are located in the epithelial walls of the utricle and saccule in the vestibular complex. Contain hair cells to detect the orientation of the stationary head and linear acceleration of the moving head. (b): Macular wall is composed of hair cells, supporting cells, and endings of the vestibular branch of the eighth cranial nerve. Covered by a gelatinous otolithic layer or membrane. (c): Hair cell with numerous straight stereocilia

Otoliths are crystalline structures in the outer part of the otolithic membrane. Composed of calcium carbonate on a matrix of proteoglycans. Facilitates bending of the kilocilia and stereocilia embedded in this membrane by gravity or movement of the head.

(a): Two types of hair cells. Basal ends of type I hair cells are rounded and enclosed within a nerve calyx on the afferent fiber. Type II hair cells are columnar and associated with typical bouton synaptic connections to their afferents. (b): Electron—dense region containing cation channels and proteins involved in mechanoelectric transduction (MET) that convert mechanical activity of the stereocilia to electric activity within the hair cell. Neighboring stereocilia are connected by various side links composed of proteins.

Expanded end- ampulla.

Wall of each ampulla is raised as a ridge called crista ampullaris.

Hair cells of crista epithelium with hair bundles project into a dome—shape proteoglycan called cupula.

Cupula is attached to opposite wall opposite and is moved by endolymph.

Basilar membrane (BM)Tectorial membrane (TM)Spiral limbus (SL) Inner (IHC) Outer hair cells (OHC). Supporting cells: Inner phalangeal (IP) Outer phalangeal cells (OP)Inner (IPC) and outer pillar cells (OPC) Inner tunnel (IT) Other supporting cells (SC) Outer tunnel (OT)Cochlear nerve (CN)

spiral organ (SO)cochlear duct (CD)stria vascularis (STV)bone (B)scala vestibuli (SV)scala tympani (ST)spiral ganglion (SG)

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Eye and Ear Histology