the eye histo
TRANSCRIPT
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Special Sensory Organ
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The Eye
The Eye is a highly specialized organ forphotoreception.
Photoreception conversion of light energy
into nerve action potentials Photoreceptors modified of dendrites of
nerve cells that receive the light tointerpret.
Two Types of Photoreceptors: 1. Rod Cells
2. Cone Cells
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The Eye
Rod Cells
Receptive to light at Different intensities
Percieves images in black and white
Cone Cells
Three functional types that are receptiveto the colors Blue, Green and Red.
Percieves Colored Images
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The Eye
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The Eye
Rod cells, Cone cells and someintegrating neurons are located in theinner layer of the eye, the Retina.
The remaining structures support theretina or focus on images of the visualworld
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The Eye
Accessory Structures for protectionagainst external damage:
1. Eyelids
Consist of a dense fibroelastic plate(Tarsal plate) covered externally by thinfolded skin and internally by the
conjunctiva
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The Eye
Within Tarsal Plates:
Meibomian Glands- Modified SebaceousGlands
Associated With Eyelashes: Glands of Zeis Sebaceous Glands
Glands of Moll Modified apocrine
sweat glands Function- prevents evaporation of tears
in tear layer
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The Eye
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The Eye
2. Lacrimal Glands Paired AlmondShaped Glands; secretes tears
Tears- contains antibacterial lysozyme
and electrolytes
3. Conjunctiva thin transparent tissuethat covers the outer surface of the eye.
Melanocytes are found in the basal layer
Stratified Columnar with goblet cells
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The Eye
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The Eye
The Eye is made up of three basiclayers:
1. Corneo-Scleral Layer (outer)
2. Uveal Layer (Intermediate)
3. Retinal Layer (inner)
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Corneo-scleral Layer
This Layer forms a tough, fibroelasticcapsule that supports the eye.
Its parts include:
1. The Sclera opaque and providesinsertion for extraocular muscles.(Posterior Five sixths of the Layer)
Consists of dense fibroelastic tissue
arranged in bundles parallel to the surface Contains very little ground substances and
fibroblasts
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Cornea-Scleral Layer
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Corneo-Scleral Layer
2. The Cornea Transparent layer thatis the principal refracting medium of theeye and roughly focuses an image unto
the retina Outer Surface is lined by Stratified
Squamous non keratinized epithelium
Epithelium rests upon thin basal laminasupported by a thick corneal stroma(Bownmans Membrane)
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Cornea-Scleral Layer
Substantia Propria (Stroma) Bulk ofthe cornea of Dense collagenous tissueforming thin lamellae.
Keratocytes- fibroblasts with elongatednuclei scattered between the lamellae.
Inner Surface lined by flattened
endothelial cells which is supported by athick basement membrane (DescemetsMembrane)
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Cornea Scleral Layer
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Cornea-Scleral Layer
Focusing power of the Cornea dependsmainly on the radius of the curvature ofits external surface.
Limbus Corneo-Scleral Junction
Conjunctiva covers the surface of theeye
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Corneo-Scleral Layer
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Uveal layer
The Middle Uveal layer is a highlyvascularized layer made of three maincomponents:
1. Choroid
2. Ciliary body
3.Iris
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Uveal Layer
Choroid
Lies between Sclera and Retina in theposterior five-sixths of the eye
It provides support for the retina
Heavily pigmented for absorbing lightthat comes through retina
Choroid merges with the ciliary bodyanteriorly
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Uveal Layer
Ciliary body
Surrounds the coronal equator of the lens
Attached to lens by the suspensory
ligament or zonule. Lens- Biconvex transparent structure (the
shape can provide varied fine focus of thecorneal images to the retina)
Shape of lens is controlled by smoothmuscle and suspensory ligament in ciliarybody.
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Uveal Layer
The Ciliary Body, the lens and thesuspensory ligament divide the eye intoa large compartment containing a thick
gel called the Viteous body. Also divides the eye into compartment
part in front containing a watery fluid
called the Aqueous humor.
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Uveal Layer
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Uveal Layer
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Uveal Layer
The Iris forms a diaphragm extending in front of the
lens.
Divides the anterior compartment into twochambers: the anterior and posteriorchambers
Highly pigmented It is an adjustable diaphragm which
regulates the amount of light reaching theretina.
Pupil aperture of the iris
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Uveal Layer
Mass of the Iris is made of loose highlyvascularized tissue.
Anterior Layer - irregular with a
discontinuous layer of firbroblasts andmelanocytes
Posterior surface Two Layers:
1. surface layer heavily pigmented Deep layer lightly pigmented
myoepithelial cells (Dilator Pupillae muscle)
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Uveal Layer
Constrictor Pupillae constrictor muscleof the iris
Smooth muscle situated in the stroma
near to the edge of the iris
Note: Contrictor Pupillae
Parasymphathetic Dilator Pupillae - Sympathetic
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Uveal Layer
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Uveal Layer
Ciliary Body secretes aqueous humorinto the posterior chamber to the pupil tothe anterior chamber and then drained
at the canal of schlemm.
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Uveal Layer
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Uveal Layer
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Uveal Layer
Posterior Compartment of the eye containsVitreous Body
Vitreous Body is a transparent gel which:
1. Supports retina and lens 2. provides an optical medium which is
non-refractive.
3. contains the hyaloid canal which extendsfrom the exit of the optic nerve to theposterior surface of the lens
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Uveal Canal
Hyaloid Canal represents the courseof hyaloid artery that supplies thevitreous body during development.
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Uveal Layer
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Retinal Layer
Photosensitive layer
Forms the inner lining of the posterior
compartment and terminates along ascalloped line , the ora serrata
Anterior to ora serrata, the retinal layerbecomes a non photosensitive epithelial
layer Retina separated to Choroid by Bruchs
Membrane
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Retinal Layer
Visual Axis
Axis passes through a depression in theretina called the fovea
Fovea is surrounded by a yellow-pigmented zone, the macula lutea
Fovea is the area of greatest visual
acuity
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Retinal Layer
Afferent nerve fibres from the retinaconverge to form the optic nerve.
Optic nerve leaves the eye via the
lamina cribosa
Retina over the lamina cribosa is calledthe optic disc (papilla) and is devoid of
photoreceptors and is a blind spot
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Retinal Layer
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Retinal Layer
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Retina
Retina made up of three cell types:Neurones, Pigment epithelial cells andneurone support cells.
Neurones are further divided into:photoreceptor cells, afferent fiber cellsand intergrating neurones
Intergrating Neurones are further dividedinto: bipolar cells, horizontal cells andamacrine cells.
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Retina
Retina divided into ten distinct histologicallayers:
1. Outermost layer pigmented epithelialcells
2. Photoreceptor layer rod and cone cellprocesses
3. Outer limiting membrane thin eosinophilic
layer4. Outer nuclear layer densely packed
nuclei
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Retina
5. Outer Plexiform Layer synapticconnections between the short axons ofthe photoreceptor cells and integratingneurones.
6. Inner Nuclear Layer Intergratingneurones
7. Inner Plexiform layer synaptic
connections between intergratingneurones and dendrites of neuroneswhose axons form the optic tract.
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Retina
8. Ganglion cell layer- Retinal Ganglioncells
9. Afferent fibre layer- afferent fibres
passing through optic disc to form theoptic nerve
10. Inner limiting membrane
demarcates the innermost aspect of theretina from the Vitreous Body
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Retina
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Retina
Muller Cells provide structural supportto the retinal layers
Extremely elongated cell found between
the inner and outer limiting membranes May also mediate the transfer of
essential metabolites to the retinal
neurones.
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Retina
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Lens
The Lens is an elastic BiconcaveStructure.
Lens cells are highly modified epithelial
cells derived from the ectoderm whichforms a lens pit overlying the embryonicoptic vesicle.
Lens Fibers are packed with proteinscalled crystallins
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Lens
Whole lens is covered by the lenscapsule which is a thick epithelialbasement membrane.
Lens Capsule is connected to ciliarybody via suspensory ligament
Anterior surface of the lens is covered
by a single layer of cuboidal cells
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Lens