The Eye Histo

8/3/2019 The Eye Histo

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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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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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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

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The Eye Histo

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