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?

Collagen matrix of the stroma Signup and view all the answers

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

Squamous epithelial cells Signup and view all the answers

Which membrane is described as an amorphous collagen layer?

Bowman’s membrane Signup and view all the answers

What is the approximate refractive power of the cornea?

43 Dioptres Signup and view all the answers

Where is the corneal thickness greatest?

At the center Signup and view all the answers

What type of collagen primarily composes the stromal collagen fibrils?

Type I collagen Signup and view all the answers

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

To produce and maintain extracellular matrix homeostasis Signup and view all the answers

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

Due to precise fibre organization and ECM structure Signup and view all the answers

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

It is produced continuously and thickens Signup and view all the answers

Which property of endothelial cells is affected by aging?

Decrease in cell number Signup and view all the answers

Where are keratocytes primarily located in the corneal stroma?

Between stromal lamellae Signup and view all the answers

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

Descemet's membrane Signup and view all the answers

What potential condition may result from excessive keratocyte cell death?

Keratoconus Signup and view all the answers

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

Preventing tear film inflow Signup and view all the answers

What is the characteristic feature of Bowman's Layer?

Acellular and non-regenerating Signup and view all the answers

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

Desmosomes Signup and view all the answers

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

Type I collagen and proteoglycans Signup and view all the answers

How thick is Bowman's Layer in the cornea?

8-15 µM Signup and view all the answers

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

Glycocalyx Signup and view all the answers

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

Keratocytes and fibroblasts Signup and view all the answers

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

Provide a barrier to pathogens Signup and view all the answers

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.