histology of the eye
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Batari Todja Umar
HISTOLOGY OF THE EYEHISTOLOGY OF THE EYE
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Spherical structure, ± 25 mm in diameter Suspended in the bony orbital socket 6 extrinsic
muscles Wall of the eye 3 concentric layers
Fibrous tunic Vascular tunic Nerve tunic
THE EYE
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A thick fibrous layer, covers the posterior 5/6 of the eyeball
Divided into 3 layers : Episclera
External layer Loose connective tissue adjacent to
the periorbital fat Stroma (Substantia propria)
= Tenon’s capsule Composed of dense network of thick
collagen fibers
SCLERASCLERA
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• Lamina Fushcae Inner aspect, adjacent to the choroid
Contains of thinner collagen & elastic fibers
Melanocyte
Function :Protects & maintains the shape and the volume of the eyeball
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• Transitional zone between the cornea & sclera
• 1.5 – 2 mm wide, 1 mm thick
• Iridocorneal angle apparatus for the outflow of the aqueous humor trabecular meshwork
Corneoscleral LimbusCorneoscleral Limbus
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Transparent, 0.5 mm thick at the center, avascular, 5 layers
Cornea
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Corneal epithelium
• Non-keratinizing squamous epithelium
• Basal cell layer gives rise to 5-7 superficial layers
• Free nerve endings terminate in this epithelium
• Adheres to the adjacent cells by desmosomes
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Bowman’s Membrane• ± 8-10 µm thick• Composed of fine
collagen fibrils• Barrier to the
spread of infection• Not regenerate
Corneal stroma• Constitutes 90% of
the corneal thickness
• Composed of about 60 thin lamellae
• Each lamellae consist of parallel bundles of colagen fibrils
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Descemet membrane• Basal lamina of
endothelial cells• Homogen• Elastic,
transparent• 7 – 10 µm
Corneal endothelium• A single layer of
squamous cells • Metabolic exchange
between the cornea & aqueous humor
• Precise regulation of the water content of the stroma maintain the transparency
• Physical & metabolic changes corneal swelling
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The most anterior part of the vascular tunic, forms a contractile diaphragm in front of the lens, a circular apperture (pupil) changes in size in response to the light intensity. Eye colour is determined by the relative number of melanocytes
IRISIRIS
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Composed of 4 layers Anterior limiting membrane
Fibroblastic & melanocyte cells Stroma
Loose fibrocollagenous support tissue Blood vessels, nerve, melanin pigment Sphincter muscle of the pupil
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Epithelial layer • Anterior non-pigmented
epithelium • Dilator pupillae muscle
• Posterior pigment epithelium• Faces the posterior chamber of the eye
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• Triangular shape • Extends from the base of the iris to the ora serrata
• 2 anatomical regions• Pars plica • Pars plana
• Function :• Aqueous humor production• Acomodation process
Cilliary Body
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• The layers are similar to the iris
• Consist of :• Stroma
• Outer layer of smooth muscle cilliary muscle
Meridional (longitudinal portion)
Radial (oblique portion)
Circular portion
• Inner vascular region extends into the cilliary process
Continuous with the vascular layer of the choroid
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• Epithelial layers• 3 principal functions
• Secretion of aqueous humor• Paticipation in blood aqueous barrier• Secretion & anchoring the zonula fibers
• The inner cells layer non-pigmented• The outer cells layer pigmented
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• Dark-brown vascular sheet, 0.25 mm thick posteriorly, 0.1 mm thick anteriorly
• Lies between the sclera & retina
• Supports the retina• Contains of :
• Suprachoroid lamina• ± 30 µm thick• Loose connective
tissue• Choroidal stroma
• Numerous venules & arterioles
• Haller layer (outer part)
• Sattler layer (inner part
CHOROID
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Choriocapillary• Capillary layer supporting the deep layer of the retina • Diameter 40 – 60 µm• Thin wall
4. Bruch’s membrane• 1-4 µm thick• Interface between the choroid & the retinal pigment
epithelium
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10 layers1. Retinal pigment
epithelium2. Photoreceptor cells3. Outer limiting membrane4. Outer nuclear layer 5. Outer plexiform layer6. Inner nuclear layer 7. Inner plexiform layer 8. Ganglion cells9. Nerve fiber layer10. Inner limiting
membrane
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RETINA
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Retinal Layers
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Retinal Pigment Epithelium
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Photoreceptor cells
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• LENSTransparent, avascular, biconvex Suspended between the edges of cilliary body zonula fibers9 mm in diameter, 3.5 mm thick Capsule
• A thick basal lamina• Produced by the anterior lens cells
Subcapsular epithelium Cuboidal layer of cells Only on the anterior surface of the lens
Lens fibers Derived from subcapsular epithelial cells
REFRACTIVE MEDIA OF THE EYE
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• Vitreous Body
• Between the lens & the retina • Transparent gelatinous structure• Attach to the surrounding structures • Main portion is homogenous gel containing 99% water, collagen, hyaluronate acid
• Avascular
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• Conjunctiva• A translucent membrane• Extends from corneoscleral limbus - internal surface of the eyelid
• 2 layers• Stratified columnar epithelium
Goblet cells mucin• Lamina propria
Loose connective tissue Blood vessels & lymphatic vessels
ACCESORY COMPONENTS OF THE EYE
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• Palpebra• Upper & lower eyelid • Protection of the eye • Contains of :
• Skin• Orbicularis oculi muscle
• Tarsal plate• Conjunctiva• Glands
Meibomian glands Sebaceous type Oily layer of the tear film
Embedded in the tarsal plate
Glands of Zeis Sebaceous glands
Glands of Moll Apocrine sweat glands
Glands of Krause Fornix conjunctiva
Glands of Wolfring Above the tarsal plate
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Lacrimal apparatus• Lacrimal glands
• Upper lateral side of the orbit
• 2 parts : orbital & palpebral parts
• 10 – 20 ducts• Several separate lobules of tubuloacinar serous glands
• Drains into the upper fornix
• Wash over the surface of the eye
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• Tears drain from the eye through lacrimal puncta
• Lacrimal canaliculi at medial angle,
• Merge into common lacrimal duct
• Open into lacrimal sac, pseudostratified ciliated epithelium
• Continuous to nasolacrimal duct open to nasal cavity below the inferior turbinate
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