Podcast
Questions and Answers
Which of the following accurately describes the outer fibrous supporting layer of the eye?
Which of the following accurately describes the outer fibrous supporting layer of the eye?
- It contains the sclera and iris, with the sclera being the most anterior part.
- It includes both the cornea and sclera, with the cornea being the transparent portion. (correct)
- It consists of the cornea and sclera, with the cornea being the denser part.
- It is composed of the cornea and choroid, where the choroid is non-vascular.
Which chamber of the eye is located between the lens and the posterior surface of the iris?
Which chamber of the eye is located between the lens and the posterior surface of the iris?
- Accessory chamber
- Vitreous chamber
- Posterior chamber (correct)
- Anterior chamber
What is the primary function of the vitreous body in the eye?
What is the primary function of the vitreous body in the eye?
- To facilitate light refraction through the eye
- To support the structure of the cornea
- To absorb excess light to prevent glare
- To maintain the shape of the eye and protect the retina (correct)
Which layer of the eye contains the outer retinal pigment epithelium and the inner neural retina?
Which layer of the eye contains the outer retinal pigment epithelium and the inner neural retina?
What structure connects the lens to the ciliary body in the eye?
What structure connects the lens to the ciliary body in the eye?
What is the primary role of the basal layer of the corneal epithelium?
What is the primary role of the basal layer of the corneal epithelium?
Bowman's membrane is primarily characterized by which of the following features?
Bowman's membrane is primarily characterized by which of the following features?
Which statement best describes the stromal layer of the cornea?
Which statement best describes the stromal layer of the cornea?
How does Bowman's membrane heal after injury?
How does Bowman's membrane heal after injury?
What is the composition of the collagen fibrils in the stroma?
What is the composition of the collagen fibrils in the stroma?
What is the main role of Descemet’s endothelium in the cornea?
What is the main role of Descemet’s endothelium in the cornea?
Which component is NOT involved in the transparency of the cornea?
Which component is NOT involved in the transparency of the cornea?
How does the cornea primarily receive its nutrients?
How does the cornea primarily receive its nutrients?
What characterizes the composition of Descemet’s membrane?
What characterizes the composition of Descemet’s membrane?
Which of the following is true about corneal corpuscles?
Which of the following is true about corneal corpuscles?
Why does damage to Descemet’s endothelium lead to corneal swelling?
Why does damage to Descemet’s endothelium lead to corneal swelling?
What surgical procedure involves changing the curvature of the cornea?
What surgical procedure involves changing the curvature of the cornea?
What is the primary reason for the cornea's optimal light refraction?
What is the primary reason for the cornea's optimal light refraction?
What is a key characteristic of corneal transplantation?
What is a key characteristic of corneal transplantation?
Flashcards
Fibrous coat
Fibrous coat
The outermost layer of the eye, composed of transparent cornea at the front and opaque sclera at the back, providing structural support and protection.
Cornea
Cornea
The clear, avascular, and highly innervated front portion of the fibrous coat. It plays a crucial role in focusing light onto the retina.
Sclera
Sclera
The opaque, white, and fibrous posterior portion of the fibrous coat. It provides structural support and protection to the eye.
Anterior chamber
Anterior chamber
The fluid-filled space between the cornea and iris.
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Vitreous body
Vitreous body
The jelly-like substance that fills the space behind the lens. It helps maintain the shape of the eye and protects the retina.
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Bowman's membrane
Bowman's membrane
The outermost layer of the cornea, it's a thick, non-cellular, homogenous layer made of collagen fibrils. It acts as a barrier against damage and infection.
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Stroma (substantia propria)
Stroma (substantia propria)
The thickest layer of the cornea, it's made of stacked layers of collagen fibrils arranged at right angles to each other, providing strength and transparency.
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Corneal corpuscles (keratocytes)
Corneal corpuscles (keratocytes)
Found in the stroma, these cells are responsible for producing and maintaining the collagen fibrils that make up the cornea's structure.
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Descemet's membrane
Descemet's membrane
The innermost layer of the cornea, it's a thin, strong membrane that acts as a barrier and helps maintain the cornea's shape.
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Corneal epithelium
Corneal epithelium
The outermost layer of the cornea, it's a multi-layered epithelium with a remarkable ability to repair itself.
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What is the cornea?
What is the cornea?
The transparent, avascular, and highly innervated front portion of the eye that plays a crucial role in focusing light onto the retina.
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What are corneal corpuscles?
What are corneal corpuscles?
The corneal corpuscles are the cells that make up the cornea. They are responsible for producing and maintaining the collagen lamellae that give the cornea its structure.
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What is the corneal stroma?
What is the corneal stroma?
The corneal stroma is the middle layer of the cornea, composed of collagen lamellae that are organized in a parallel and regular arrangement.
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What type of collagen is found in the cornea?
What type of collagen is found in the cornea?
Type I collagen is the main type of collagen found in the cornea. It provides strength and structure to the corneal stroma.
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What is the corneal ground substance?
What is the corneal ground substance?
The corneal ground substance is a gel-like substance that fills the spaces between the collagen lamellae and helps to maintain the cornea's hydration and translucency.
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What are Proteoglycans?
What are Proteoglycans?
Proteoglycans are complex molecules found in the corneal ground substance. They help to maintain the hydration of the cornea and contribute to its clarity.
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What is Descemet's membrane?
What is Descemet's membrane?
Descemet's membrane is the posterior basement membrane of the cornea, a thick and strong layer composed of collagen fibers that provides structural support and acts as a barrier.
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What is the corneal endothelium?
What is the corneal endothelium?
The corneal endothelium is a single layer of cells that lines the inner surface of the cornea, responsible for maintaining the cornea's hydration, transparency, and metabolic exchange with the aqueous humor.
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Why is the cornea avascular?
Why is the cornea avascular?
Avascular means lacking blood vessels. The cornea's avascular nature contributes to its transparency, as blood vessels would scatter light and affect its clarity.
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How does the cornea receive its nourishment?
How does the cornea receive its nourishment?
The cornea receives its nutrients from the aqueous humor in the center and the vessels in the limbus at the periphery. The cornea also receives oxygen directly from the atmosphere.
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Course Information
- Course: BMS302
- Lecture: 1
- Topic: Eye
- Instructor: Dr. Manal Shaaban Hafez
- Institution: Galala University
- Semester: Fall 2024
Intended Learning Outcomes
- List the three coats of the eye
- Determine the eye chambers
- Describe the structure and correlated function of the cornea
- Describe the structure and correlated function of the sclera
- Determine the structural changes at the corneoscleral junction and its importance
Eye Ball Structure
- Fibrous Tunic:
- Sclera (opaque, posterior 5/6 of the fibrous coat)
- Cornea (transparent, anterior 1/6)
- Vascular Tunic
- Choroid (melanocytes, macrophages and connective tissue)
- Ciliary body
- Iris
- Sensory Tunic / Inner Layer
- Retina (Pigmented + Neural)
Layers of Eye Ball
- 1-Outer fibrous supporting layer:
- A-Cornea (anterior transparent 1/6)
- B-Sclera (posterior dense opaque 5/6)
- 2-Middle vascular layer (uveal layer)
- A-Choroid
- B-Ciliary body (contains ciliary muscle, ciliary processes and zonular fibers)
- C-Iris (contains pupil, sphincte pupillae and dilator pupillae)
- 3-Inner sensory layer:
- A. Outer retinal pigment epithelium
- B. Inner neural retina
Eye Chambers
- 1- Anterior chamber: Filled with aqueous humor, between cornea and anterior surface of the iris.
- 2- Posterior chamber: Filled with aqueous humor, between posterior surface of iris and lens. The lens is a transparent biconvex structure attached to the ciliary body by zonular fibers.
- 3- Vitreous chamber: Filled with vitreous body (a gel-like substance), behind the lens and surrounded by the retina.
Cornea Structure
- Anterior 1/6 of the fibrous coat
- Transparent and avascular
- Highly innervated
- Thin in center (0.5 mm)
- Thick in periphery (1 mm)
- Five layers: epithelium, Bowman's membrane, stroma, Descemet's membrane, endothelium
Corneal Epithelium
- Stratified squamous, non-keratinized epithelium
- Adheres by desmosomes
- 5-6 layers thick, resting on a thick basement membrane (8-12 µm)
- Superficial cells have microvilli to keep the cornea wet
- Intermediate cells are polygonal and have free nerve endings
- Basal layer is cuboidal, has high regenerative power by mitosis
Bowman's Membrane
- Thick, homogenous, non-cellular layer
- Basement membrane of the stratified epithelium
- Synthesized by corneal epithelium and stromal cells
- Protective barrier against mechanical injuries and bacterial invasion
- Does not regenerate, heals by fibrous tissue, causing corneal opacities
- Ends abruptly at the corneoscleral limbus
Stroma (Substantia Propria)
- Thickest layer (90%)
- Non-vascular
- Regular lamellae of parallel collagen fibrils (arranged at right angles)
- Fibroblasts and keratocytes are arranged in rows
- Immersed in ground substance (proteoglycans)
- Maintains collagen lamella organization and spacing
Descemet's Membrane
- Homogeneous, thick basal lamina
- Formed from collagen fibers by the underlying endothelial cells
- Continuously synthesized by the underlying endothelium
- Readily regenerates after injury
Descemet's Endothelium
- Simple squamous cells lining the inner surface
- Active in protein synthesis & maintains the basement membrane
- Responsible for Na+ pumping, water removal to maintain corneal hydration & transparency
- Contains pinocytotic vesicles (maintain optimal light refraction)
- Metabolic exchange between cornea and aqueous humor
- Damage leads to corneal swelling
Corneal Nutrition
- Receives nutrition from aqueous humor (center)
- Receives nutrition from vessels in the limbus (periphery)
- Receives oxygen from the atmosphere.
Corneal Transparency
- Lacks vascular & lymphatic drainage
- Regular arrangement of components
- Similar refractive indices of components
- Continuous fluid withdrawal from the stroma.
Medical Applications
- Corneal transplantation
- LASIK surgery (for myopia, hyperopia, astigmatism)
- Physical or metabolic damage to endothelial cells can lead to rapid corneal swelling, which can result in corneal opacity.
Conjunctiva
- Thin, transparent mucosa
- Bulbar conjunctiva: covers exposed sclera
- Palpebral conjunctiva: lines internal surface of eyelids
- Stratified columnar epithelium (goblet cells present)
- Loose connective tissue (lymphocytes, macrophages)
Conjunctiva Functions
- Lubrication & protection
- Defense (immune response)
- Drainage of aqueous humor
Corneo-scleral Junction (Limbus)
- Transition zone between cornea and sclera
- Transparent corneal stroma merges with the opaque sclera
- Limbus is highly vascularized, provides metabolites to corneal cells by diffusion
- It contains the trabecular meshwork, Canal of Schlemm, and important stem cells for corneal maintenance.
- Critical elements for drainage of aqueous humor
Importance of Limbus
- Basal epithelial layer contains stem cells for corneal maintenance
- Stem cells at limbus creates a conjunctival barrier
- Trabecular meshwork and Canal of Schlemm drain aqueous humor
Histological Changes of Corneoscleral Junction (Limbus)
- Corneal epithelium thickens, continuous with bulbar conjunctiva
- Bowman's membrane ends and is replaced by subconjunctival supportive tissue
- Stroma becomes sclera with less regular collagen bundles
- Consists of a circular Canal of Schlemm
Descemet's Membrane in Corneoscleral Junction
- Descemet's membrane splits to form trabecular meshwork
- Descemet's endothelium lines trabecular meshwork and canal of Schlemm
- Canal of Schlemm and trabecular meshwork are located in the iridocorneal angle.
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