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Questions and Answers
What are the five layers that make up the cornea?
Epithelium, Bowman’s layer, Stroma, Descemet’s membrane, Endothelium
Why is the cornea isolated from the blood supply?
To maintain transparency.
What is the role of the squamous stratified epithelium in the cornea?
It provides an optically smooth front surface to the cornea.
Which layer of the cornea is a passive barrier, stopping water from entering the stroma below?
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What provides strength, elasticity, and form to the cornea?
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Which layer of the cornea consists of narrow collagen fibrils and is around 12μm thick?
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What are the three types of cells present in the epithelium of the cornea?
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What percentage of the total refractive power of the eye is contributed by the cornea?
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What is ptosis, and which muscle is primarily involved in it?
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What are the three layers of the tear film, and what percentage of tears are produced by the accessory glands?
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What is the structural form of a collagen molecule, and which type of muscle is Müller's muscle?
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What is the function of the plica semilunaris, and which part of the brain influences the lacrimal gland?
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What is the thickness of the sclera in the posterior region?
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What is the function of the limbus in relation to the cornea?
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What type of fibers are present in the sclera?
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What is the origin of the corneal nerves?
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What is the characteristic of the terminal axons in the cornea?
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Study Notes
Cornea Anatomy
- The cornea has five layers: epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium.
- The epithelium is the most anterior layer, 5-6 cells thick, and 50μm thick.
- The epithelium is a stratified squamous epithelium, consisting of three types of cells: squamous, wing, and basal.
- These cells undergo a 10-day cycle, with basal cells capable of division and repair.
Corneal Epithelium
- The epithelium provides an optically smooth front surface to the cornea, along with the tear film.
- Cells are bound together by desmosomes, and basal cells have gap junctions.
- The epithelium is a passive barrier, stopping water from entering the stroma below.
Bowman's Layer
- Bowman's layer is a modified portion of the stroma, with no cells and narrow collagen fibrils.
- It is 12μm thick, and some species lack a Bowman's layer.
Corneal Stroma
- The stroma provides strength, elasticity, and form to the cornea.
- It is comprised of collagen, with a triple alpha-helix structure.
- The stroma makes up most of the cornea.
Limbus
- The limbus is the site of nourishment of the peripheral cornea.
- It is involved in corneal wound healing and immunosurveillance.
- It contains pathways of aqueous humor outflow and circumferential or tangential collagen fibrils.
- It is the site of surgical incisions.
Sclera
- The sclera is the outer coat of the eye, containing collagen, proteoglycans, and elastic fibers.
- It is relatively avascular, with a thickness of 1mm (posterior) and 0.4mm behind muscle tendon insertions.
- The sclera has variable fibril diameter.
Corneal Nerves
- Corneal nerves are derived from the ophthalmic division of the trigeminal nerve.
- Branches radiate to the anterior cornea from the limbus, and nerves lose their myelin sheaths in the cornea.
- Terminal axons are very sensitive to pain and temperature.
Tear Film
- The tear film has three layers: lipid, aqueous, and mucous.
- The accessory glands produce 10% of tears.
Ptosis
- Ptosis is the drooping of the upper eyelid.
- The main muscle involved in ptosis is the levator aponeurosis.
Lacrimal Gland
- The lacrimal gland is under the influence of the hypothalamus.
- The lacrimal gland is innervated by sensory, parasympathetic, and sympathetic nerves.
Miscellaneous
- The plica semilunaris is a vestigial "third eyelid".
- The drainage system of tears is thought to be driven by pressure gradients.
- Dr. Regini belongs to the Llandaff RC rowing club.
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Description
Test your knowledge on the anatomy and properties of the cornea, focusing on its structure, dimensions, refraction capabilities, and more.
