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Histology of the Eye

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Histology of the Eye Histology of the Eye ◧ Editing file ◧ Important ◧ Doctor notes / Extra 438 Histology Team Neuropsychiatry Block Objectives: By the end of this lecture, the student should be able to describe: ◧ The general structure of the eye. ◧ The microscopic structure of: ▪ Cornea ▪ Retina. 438 Histology Team - Neuropsychiatry Block 2 Eye bulb Three coats (3 Tunics) 1- Fibrous tunic: Cornea. Sclera. 2- Vascular tunic: highly vascular +pigmented Choroid. Ciliary body. Iris. 3- Neural tunic: formation of image Retina. 438 Histology Team - Neuropsychiatry Block 3 ◧ Fibrous tunic: Cornea It is the transparent, avascular and highly innervated anterior portion of Definition the fibrous coat. Corneal - Non-keratinized Stratified squamous epithelium. epithelium - Contains numerous free nerve endings. Pain receptors Bowman’s - It is homogenous non-cellular layer containing type I membrane collagen fibrils. - It is the thickest layer (about 90%). - It is composed of parallel lamellae of dense Stroma collagenous C.T. Regular arrangement to make it transparent - Each lamella is composed mainly of parallel type I collagen fibers with long fibroblasts. Descemet’s It is a thick basement membrane. membrane It is simple squamous epithelium. Layers of cornea Layers Corneal Functions: dehydration aids in transparency Layers of cornea Layers endothelium 1- Formation of Descemet’s membrane. 2- Keeping the stroma relatively dehydrated (sod. pump → water withdrawal from the stroma). 438 Histology Team - Neuropsychiatry Block 4 ◧ Fibrous tunic: Limbus (corneo scleral junction) • It is the transition region between the cornea and sclera. • It is about 1.5 mm width. • It is highly vascular. Provide nutrition to the cornea • It contains: 1. Trabecular meshwork: Endothelium-lined spaces. It leads to canal of Schlemm. 2. Canal of Schlemm: It drains the aqueous humor into the venous system. ◧ Fibrous tunic: Sclera Cornea Canal of Schlemm • It covers the posterior 5/6 of the fibrous tunic. Iris • Sclera Proper: consists of interlacing bundles of type I collagen (dense collagenous C.T. irregular Sclera type). Ciliary • Melanocytes are located in the deeper regions. body 438 Histology Team - Neuropsychiatry Block 5 Vascular tunic Choroid Ciliary body Ciliary processes It is the vascular, pigmented It is the anterior continuation of the choroid. It • Processes project from the inner posterior portion of the middle surrounds the lens. surface of the anterior 1/3 of the vascular tunic. ciliary body towards the lens. Structure: • Are covered by pars ciliaris Structure: • It is formed of loose vascular and pigmented retinae (2 rows of columnar cells). • It is composed mainly of C.T. that contains 3 bundles of smooth muscle • They give attachment to the loose C.T. with melanocytes. cells (ciliary muscle). lens suspensory ligaments • It is separated from the • Its inner surface is lined by pars ciliaris retinae ( (zonule fibers). retina by its Bruch’s 2 rows of columnar cells; outer pigmented and membrane. inner non- pigmented layers) . • Its inner surface is highly folded forming the ciliary processes. 438 Histology Team - Neuropsychiatry Block 6 ◧ Vascular tunic: Iris Incomplete layer of fibroblasts and 1- Anterior border layer melanocytes. Poorly vascularized C.T. with fibroblasts and 2- Stroma melanocytes. Pigments are responsible for the eye color Well-vascularized loose C.T. Centrally, it contains circularly arranged 3- Vessel layer smooth muscle fibers (sphincter pupillae muscle). 4- Dilator pupillae Contains radially arranged myoepithelial muscle layer cells. It is formed of 5 layers: It is formed It is composed of 2 rows of pigmented 5- Posterior surface epithelial cells (pars iridis retinae). layer They are the continuation of pars ciliaris retinae. 438 Histology Team - Neuropsychiatry Block 7 ◧ Neural tunic: Retina It is composed of 10 distinct layers (from Light outside to inside): 1.Pigmented epithelium. (outermost) 2.Rods and cones layer. 3.Outer limiting membrane. 4.Outer nuclear layer. 5.Outer plexiform layer. 6.Inner nuclear layer. 7.Inner plexiform layer. 8.Ganglion cell layer. 9.Optic nerve fiber layer. 10.Inner limiting layer. (innermost) 438 Histology Team - Neuropsychiatry Block 8 Layers Of Retina 4- Outer 1- Pigmented Epithelium: 2- Rods and cones layer 3- Outer limiting membrane nuclear layer • Cuboidal to columnar cells Are photoreceptor cells. A region of zonulae Contains nuclei of (single layer). Each has: adherents junctions the rods & cones. • Apical microvilli. (to increase 1. Dendrite formed of: between Muller cells surface area) • Outer segment: contains and the • Abundance of melanin membranous discs containing photoreceptors granules. rhodopsin (in rods) and iodopsin (in cones). Functions: • Connecting Stalk: with modified 1. Absorb light. cilium. 2. Phagocytosis of membranous • Inner segment discs from tips of rods. 2. Cell body. 3. Esterification (Activation) of 3. Axon: synapses with dendrite of Vitamin A (in SER). bipolar neuron of inner nuclear layer. Functions: 1. Rods are receptors for dim light ( low intensity light). 2. Cones are receptors for bright light and color vision (red, green & blue). 438 Histology Team - Neuropsychiatry Block 9 . Layers Of Retina 7- Inner plexiform 10- The inner 5- Outer plexiform 8- Ganglion 9- Optic nerve fiber 6- Inner nuclear layer: layer: limiting layer: cell layer: layer: membrane: Contains Contains the nuclei of: Contains Contains cell Contains It is formed by axodendritic axodendritic bodies of large unmyelinated axons of the basal synapses between 1. Bipolar neurons. synapses between multipolar the ganglion cells. laminae of the the photoreceptor 2. Horizontal neurons. axons of bipolar neurons of the Muller cells. cells and dendrites 3. Amacrine neurons neurons and ganglion cells. N.B. These axons of bipolar and (unipolar neurons) dendrites of become myelinated as horizontal cells. 4. Neuroglial cells (Muller ganglion cells and the nerve pierces the cells) that extend amacrine cells. sclera. between the vitreous body and the inner segments of rods and cones. 438 Histology Team - Neuropsychiatry Block 10 Retina cont. Fovea centralis: Types of cells in the retina: It lies in the center of macula 1- Pigmented epithelium. 2- Nerve cells: lutea. • Photoreceptor cells (rods & cones) Cones are highly • Bipolar neurons. concentrated in the fovea. • Ganglion cells. It is responsible for visual • Association neurons: acuity. - Horizontal cells. - Amacrine cells. 3- Neuroglial cells: - Muller’s cells. - Astrocytes. 438 Histology Team - Neuropsychiatry Block 11 Conjunctiva It is the transparent mucous membrane lining the inner surfaces of the eyelids (palpebral conjunctiva) and reflecting onto the sclera of the anterior surface of the eye (bulbar conjunctiva). L/M: 1- Epithelium: Stratified columnar epithelium with numerous goblet cells (they secrete mucins on the surface of the eye). 2- Lamina propria: Loose C.T. 438 Histology Team - Neuropsychiatry Block 12 Quiz 1, which one of the following keep the stroma 4. which one of the following is poorly vascularized dehydrated in cornea : layer A. corneal epithelium A. stroma of the iris B. stroma of cornea B. stroma of the cornea C. bowman membrane C. limbus D. corneal endothelium D. vessel layer of the iris 2. Which of the following neuroglial cells are 5. from where the ciliary processes project : found in the retina? A. from inner surface of the anterior ⅓ of ciliary body A. Cones B. from outer surface of the anterior ⅓ of ciliary body B. Rods C. from inner surface of the posterior ⅓ of ciliary body C. Muller’s cells D. from outer surface of the posterior ⅓ of ciliary body D. Ganglion cells 6. dense collagenous CT irregular type found in : 3. what type of cell bodies are located in A. stroma of the cornea ganglion cell layer of the retina : B. sclera proper C. choroid A. bipolar D. vessel layer of the iris B. multipolar C. unipolar D. pseudo multipolar B 6. A 5. A 4. B 3. C 2. D 1. 13 Special thanks for Team Leaders ◧ Mohammed alhuqbani ◧ Abdullah shadid ◧ Rawan alzayed ◧ Sarah alflaij .
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