46 Questions
What contributes to the formation of the corneal stroma and the corneal endothelium?
Neural crest cells
What is the radius of curvature of the anterior transparent sphere of the cornea?
8mm
What is the refractive power of the cornea?
45D
What is the central cornea thickness?
0.53mm
From the front, how does the cornea appear?
Oval
What is the radius of curvature of the central cornea's anterior surface?
7.8mm
What is the diameter of the globe in the anteroposterior direction?
24mm
Which layer of the cornea is produced by the corneal endothelium?
Descemet's layer
What contributes to the formation of the corneal epithelium?
Surface ectoderm
What is the refractive power of the cornea in diopters (D)?
45D
What is the primary function of the cornea?
To refract light
Which layer of the cornea contains a thickened area of collagenous connective tissue known as Schwalbe’s line?
Descemet’s layer
What is the average cell density of the corneal endothelium in adults?
2500 cells/mm2
Which layer of the cornea is responsible for regulating water and ion flow from the aqueous humor?
Endothelium
Where are the corneal nerves located?
Epithelium, anterior stroma/Bowman’s layer, and midstroma
What is the total refractive power of the eye, and how much of it is attributable to the cornea?
60-65 D, 43 to 48 D
Which layer of the cornea serves as a leaky barrier between the corneal stroma and the anterior chamber?
Endothelium
What happens to the corneal endothelial cells with age?
They wear out and neighboring cells change shape and size
Which nerve innervates the cornea?
Ophthalmic nerve (V1)
What factors affect the amount of corneal refraction?
Curvature of the anterior corneal surface, change in refractive index, corneal thickness
What is the approximate thickness of Bowman's layer in the cornea?
8-14 $\mu$m
Where are the stem cells responsible for continuous replacement of the corneal epithelium located?
Around the corneal periphery
What is the main function of keratocytes in the cornea?
Synthesize collagen and extracellular matrix components
Which layer of the cornea is responsible for attracting water to create precise spacing between the lamellae?
Ground substance in the stroma
Which layer of the cornea is the true basement membrane of the endothelium?
Descemet's membrane
What contributes to the transparency of the corneal stroma?
Regular arrangement of stromal component and small diameter of the fibrils
Which layer of the cornea is the principal refracting component of the eye?
Corneal stroma
What is the main function of the corneal endothelium?
Maintain stromal hydration
Which layer of the cornea is composed of collagen fibers, keratocytes, and extracellular ground substance?
Corneal stroma
What is the approximate thickness of the corneal epithelium?
50 $\mu$m
Mention the type of junctions that are seen in the corneal epithelium
Zonula occludents(tigh junctions) Adherens junctions Desmosomes(macula adherence) Gap junctions
Which cells are the source for renewal of the corneal basal cell layer?
Stem cells
Where does migration of the basal cells occur?
From the periphery of the cornea toward the center
Since the bowman's layer is prenatally produced, it cannot regenate. What cells can replace it though?
Epithelial cells or stromal scar tissue
What is the radius of the sclera?
12
Where does the cornea fit?
Scleral foramen
The cornea has an elliptic shape
True
What covers the anterior and posterior surface of cornea?
Tear film in anterior and aqueous filled anterior chamber in posterior
The periphery of the cornea is continous with the conjunctiva and the sclera
True
How many cells thick is the epithelium?
5-7
What type of cells does the epithelium and its surface layer have?
Stratified non-keratinized epithelium
Which type of cells in the epithelium have a convex anterior surface and concave posterior surface?
Wing cells
Which layer of the cornea is acellular?
Bowman
Which of the corneal layers is also known as substantia propia?
Stroma
Which of the layers is known as the true basement membrane?
Descements
What type of cells are seen in the endothelium?
Single squamous
Study Notes
Corneal Histological Features
- The cornea is the principal refracting component of the eye and is approximately 71mm in size.
- It is transparent and avascular, providing optimal light transmittance.
- The cornea has five layers: epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium.
- The corneal epithelium is the outermost layer and is 50 μm thick, with three different layers: surface layer, wing cells, and basal layer.
- The corneal epithelium undergoes continuous replacement through cell proliferation and migration, with stem cells located around the corneal periphery.
- Bowman's layer is an acellular dense layer composed of collagen fibrils and is approximately 8-14 μm thick.
- The corneal stroma, also known as Substantia Propria, is approximately 500 μm thick and composed of collagen fibers, keratocytes, and extracellular ground substance.
- Collagen fibers in the corneal stroma form parallel layers called lamellae, contributing to corneal transparency.
- Keratocytes are fibroblasts of the cornea that synthesize collagen and extracellular matrix components.
- The ground substance in the corneal stroma contains proteoglycans, which attract water to create precise spacing between the lamellae, contributing to stromal hydration and transparency.
- Descemet's membrane is the true basement membrane of the endothelium and consists of two laminae, thickening throughout life.
- The very regular arrangement of the stromal component and the small diameter of the fibrils contribute to stromal transparency.
Test your knowledge of corneal histological features with this quiz. Explore the five layers of the cornea, including the epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium. Learn about the composition of each layer, the role of keratocytes, and the factors contributing to corneal transparency.
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