Cornea Structure and Function Quiz
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Questions and Answers

Which layer of the cornea is mainly responsible for the barrier function?

  • Stroma
  • Endothelium
  • Bowman’s membrane
  • Corneal epithelium (correct)

What is the average horizontal diameter of an adult cornea?

  • 9.8 mm
  • 11.7 mm (correct)
  • 10.0 mm
  • 12.5 mm

How thick is the corneal epithelium?

  • 50 μm (correct)
  • 200 μm
  • 100 μm
  • 20 μm

What structure primarily contributes to the cornea's transparency?

<p>Collagen matrix of the stroma (C)</p> Signup and view all the answers

Which type of cell in the cornea is responsible for maintenance of the tear film?

<p>Squamous epithelial cells (D)</p> Signup and view all the answers

Which membrane is described as an amorphous collagen layer?

<p>Bowman’s membrane (A)</p> Signup and view all the answers

What is the approximate refractive power of the cornea?

<p>43 Dioptres (C)</p> Signup and view all the answers

Where is the corneal thickness greatest?

<p>At the center (A)</p> Signup and view all the answers

What type of collagen primarily composes the stromal collagen fibrils?

<p>Type I collagen (D)</p> Signup and view all the answers

What is the primary function of keratocytes within the corneal stroma?

<p>To produce and maintain extracellular matrix homeostasis (B)</p> Signup and view all the answers

How does the organization of the stromal collagen fibrils contribute to corneal transparency?

<p>Due to precise fibre organization and ECM structure (B)</p> Signup and view all the answers

What happens to Descemet’s membrane over a person's lifetime?

<p>It is produced continuously and thickens (C)</p> Signup and view all the answers

Which property of endothelial cells is affected by aging?

<p>Decrease in cell number (A)</p> Signup and view all the answers

Where are keratocytes primarily located in the corneal stroma?

<p>Between stromal lamellae (D)</p> Signup and view all the answers

What structure serves as the basement membrane of the Corneal endothelium?

<p>Descemet's membrane (A)</p> Signup and view all the answers

What potential condition may result from excessive keratocyte cell death?

<p>Keratoconus (A)</p> Signup and view all the answers

What is the primary function of the tight junctions (zonula occludens) in the corneal epithelium?

<p>Preventing tear film inflow (D)</p> Signup and view all the answers

What is the characteristic feature of Bowman's Layer?

<p>Acellular and non-regenerating (B)</p> Signup and view all the answers

Which type of junction connects wing and basal cells in the corneal epithelium?

<p>Desmosomes (B)</p> Signup and view all the answers

What is the predominant composition of the stroma in the cornea?

<p>Type I collagen and proteoglycans (B)</p> Signup and view all the answers

How thick is Bowman's Layer in the cornea?

<p>8-15 µM (B)</p> Signup and view all the answers

Which component is primarily secreted by the plasma membrane of surface epithelial cells to bind mucin?

<p>Glycocalyx (C)</p> Signup and view all the answers

What type of cells can be found in the stroma of the cornea?

<p>Keratocytes and fibroblasts (A)</p> Signup and view all the answers

What is the primary role of intercellular junctions in the corneal epithelium?

<p>Provide a barrier to pathogens (D)</p> Signup and view all the answers

Flashcards

Cornea function

The cornea is the transparent outer layer of the eye, acting as a primary refracting surface and a protective barrier.

Cornea thickness

The cornea's thickness varies, ranging from 0.5mm centrally to 1mm in the periphery.

Corneal layers

The cornea is built of 5 distinct layers: epithelium, Bowman's membrane, stroma, Descemet's membrane, and endothelium.

Corneal Refractive Power

The cornea contributes about 2/3rds of the eye's total refractive power, approximately 43 diopters with a refractive index of 1.33.

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Corneal Epithelium

The outermost layer of the cornea, about 5-7 cell layers thick, responsible for maintaining a stable tear film and protecting the eye.

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Corneal Structure

The cornea's structure consists of layers of cells (epithelium, etc.). The cells have specific roles in maintaining transparency and vision clarity.

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Stromal Keratocytes

Cells within the corneal stroma, a key part of the cornea's structure, contributing to transparency and strength.

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Corneal Endothelium

The innermost corneal layer, a single cell layer thick with active Na/K pumps maintaining corneal water content, crucial for clarity.

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Corneal Epithelium Cells

Cells forming the outermost layer of the cornea, supported by a basement membrane and tightly connected.

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Basal-to-Squamous Differentiation

The process by which cells in the corneal epithelium change from basal cells to flat squamous cells, taking approximately 10 days.

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Intercellular Junctions

Structures that connect cells in the corneal epithelium, crucial for protection.

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Tight Junctions (Zonula Occludens)

In the corneal epithelium, these junctions prevent the passing of substances through the space between cells.

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Bowman's Layer

A thin, acellular layer beneath the corneal epithelium, providing shape and structure.

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Corneal Stroma

The main part of the cornea, composed of collagen fibrils and keratocytes, providing transparency and strength.

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Collagen Fibrils (Stroma)

Organized, uniform fibers in the stroma, providing corneal strength and structure.

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Hemidesmosomes

Attach basal cells of the cornea to the basement membrane.

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Lamellae in Cornea

Thin layers of collagen fibrils in the corneal stroma, arranged in parallel and at varying angles to each other, contributing to transparency.

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Stroma Thickness

The corneal stroma is thicker at the periphery than in the center, with collagen fibrils running circumferentially near the limbus.

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Stroma Collagen Type

The corneal stroma is primarily composed of type I collagen, with type V collagen present, forming unique narrow-diameter fibrils.

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Keratocyte Role

Keratocytes, located mostly in the anterior stroma, are responsible for synthesizing collagen and GAGs, maintaining corneal transparency and healing.

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Descemet's Membrane

A thick basement membrane of the endothelium, made of collagen fibrils and produced continuously, adding thickness throughout life.

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Endothelial Cell Features

The corneal endothelium is a single layer of hexagonal cells which don't divide or replicate after birth, acting as a 'leaky' barrier for nutrients.

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Endothelial Function

The corneal endothelium regulates corneal hydration by actively pumping ions across cell membranes, essential for transparency.

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Endothelial Cell Decline

The number of endothelial cells decreases with age, leading to potential corneal dysfunction.

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Study Notes

Cornea Structure and Function

  • The cornea is a transparent, avascular connective tissue with a smooth surface.
  • It's approximately 0.54-0.7mm thick (540-700µM)
  • It's the main structural barrier against infections.
  • It is part of the eye's principal refracting component, working alongside the tear fluid.
  • It is continuous with the conjunctiva and sclera.
  • Its transparency is due to various physiological features.

Cornea Physiology

  • Acts as a refracting surface for the eye.
  • Protects the intraocular contents.
  • Absorbs drugs.
  • Creates a barrier function between the epithelium and endothelium.
  • Utilizes active pumps, such as Na/K ATP'ase, for maintaining appropriate function.

Cornea Layers (Structure)

  • Epithelium: The outermost layer composed of corneal epithelial cells. It is 5-7 cells thick and approximately 50µM thick, containing multiple layers of cells. The cells are replaced about every seven days.
  • Bowman's Membrane: A smooth, acellular, non-regenerating layer, located between the epithelium and stroma. 8-15µM thick and made of a sheet of randomly arranged collagen fibers, not bundled.
  • Stroma: The thickest layer (90% of the cornea's total thickness; ~500µM), composed primarily of type I collagen fibrils and keratocytes (fibroblast-like cells). It's organized in lamellae, which are sheets of parallel collagen fibrils, and ~30nm in diameter. This structure is crucial for the transparency and strength of the cornea. Keratocytes are important in maintaining the stroma's homeostasis.
  • Descemet's Membrane: A lattice-work of collagen fibrils, produced continuously by the endothelium. Is 10–15µM thick. It thickens throughout life and ends at the limbus (Schwalbe's line).
  • Endothelium: The innermost layer, featuring a single layer of hexagonal cells. ~5µM thick, it is metabolically active, containing numerous mitochondria. Cells in this layer do not divide and replicate. The density of these cells declines with age.

Corneal Embryology

  • Epithelium develops from surface ectoderm.
  • Bowman's membrane and stroma originate from mesenchyme (neural crest tissue, 7 weeks).
  • Endothelium also comes from neural crest tissue.
  • Descemet's membrane is synthesized by endothelial cells.

Other Key Facts

  • The cornea provides approximately 2/3rds of the eye's total refractive power.
  • Refractive Power = 43 Diopters, Refractive Index = 1.33
  • The anterior surface is roughly convex and elliptical/oval shaped in form.
  • Horizontal diameter is typically 11-12 mm (average 11.7mm)
  • Vertical diameter is approximately 1mm smaller than the horizontal diameter.
  • Corneal thickness at the center is ~0.5mm and in the periphery ~1mm; center is thinner than the periphery.
  • The radius of curvature for the central cornea is 7.8mm, and at the posterior surface is 6.5mm.
  • At birth, the corneal diameter is 9.8mm (75-80% of the adult human size).

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Description

Test your knowledge about the structure and physiology of the cornea. This quiz covers aspects such as the cornea's layers, functions, and its role in eye health. Dive into the details of how the cornea protects the eye and maintains vision.

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