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41 Cards in this Set
- Front
- Back
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Where is Cornea located and what does it become at its periphery? |
Anterior surface: Front of the eye in contact with the atmosphere and the conjunctiva of the eyelids. It is covered by the tears film. Periphery surface: The limbus where corneal tissues meet the conjunctiva, sclera, ciliary body, iris and fascia. |
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State two functions of the cornea. |
1. To provide the eye with most of its focal power (+42.00D) 2. Mechanical protection via blink reflex |
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What are the following dimensions of the cornea? Lowest to highest: Centre and Edge thickness Posterior and anterior radius Vertical and horizontal
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Centre thickness: 0.5mm Edge thickness: 0.7mm Posterior radius: 6.7mm Anterior radius: 7.6mm Vertical: 10.6mm Horizontal: 11.6mm |
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State the layers of the cornea and their measurements. |
Epithelium (50um) Anterior Limiting Lamina (8-10um) Stroma (500um) Posterior Limiting Lamina (8-10um) Endothelium (5um) |
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Which nerve provides sensory innervation of the cornea? |
Trigeminal Nerve (Cranial Nerve V) |
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The Cornea has no real blood supply. Where else does it get its nutrients? |
Anterior surface: When eyes are open: the tears film When eyes are closed: the tarsal/palpebral conjunctiva Posterior surface: Aqueous Humour Periphery: Limbal blood vessels |
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Why is the cornea transparent? |
Avascular (no blood supply) Corneal nerves are unmyelinated Corneal epithelium and Endothelium is non-keratinised Regular arrangement of collagen fibres in Stroma. |
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How does the Cornea lose transparency if it takes on too much fluid? |
The separation of collagen fibres in the Stroma increases causing the cornea to lose its transparency. |
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What are the three types of cell in the cornea epithelium? |
Squamous Cells Wing/Umbrella Cells Columnar Cells |
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State 4 functions of the corneal epithelium. |
Damage protection through layers and sensitivity (blink reflex) Protection from foreign bodies and cell renewal A pathway for metabolites through tears Provides a smooth surface for refraction |
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What is the function of the Anterior Limiting Lamina? |
Creates a smooth surface for the basement membrane of the epithelium |
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The Stroma of the Cornea is made up of regularly arranged collagen. Why is this? |
To maintain corneal transparency. |
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State 3 functions of the Corneal Stroma? |
Maintain Cornea transparency Mechanical strength and stability Protection from internal structures |
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What is the function of the posterior Limiting Lamina? |
A basement membrane for the Endothelium |
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State 3 functions of the corneal Endothelium |
Regulates corneal hydration Active transport for metabolites from the aqueous to the Stroma Produces material for the posterior Limiting Lamina and can reform it |
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Which layer of the cornea cannot regenerate if damaged? |
Endothelium |
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What is the outer layer of the Sclera in contact with? |
Bulbar fascia/Tenons Capsule |
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What is the inner layer of the Sclera in contact with? |
The choroid |
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State 4 functions of the sclera |
Protection: physical and mechanical Reduces light Anchors the extrinsic ocular muscles Supports internal structures |
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State the thickness of the Sclera: Lowest to highest: At the Insertion of the recti muscles At equator Corneo-scleral junction At posterior pole |
Insertion of recti muscles: 0.3mm Equator: 0.5mm Corneo-scleral junction: 0.7mm Posterior pole: 1mm
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What are the radii of the Sclera? Anteriorly and posteriorly |
Anteriorly: 12.5-15mm Posteriorly: 11.5mm |
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What is the refractive index of the Cornea? |
1.376 |
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What is the Limbus? |
A zone of transition, joins the cornea to the Sclera |
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Which epithelium does the corneal epithelium transition into? |
The conjunctival epithelium |
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What layers of the cornea terminate at the limbus? |
The Anterior and posterior Limiting Laminas |
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What are the two junctions of the limbus called? |
The corneo-limbal junction The limbo-scleral junction |
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There is an important region of the limbus associated with aqueous humour drainage? What is it? |
Trabecular meshwork |
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What is the function of the scleral spur? |
Supports structures within the limbus |
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State the pathway of the aqueous when it is drained. |
Trabecular meshwork Canal of schlemm Collector channels Aqueous veins Anterior ciliary veins |
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The limbal region has six areas of blood supply. State them |
Conjunctival vessels Episcleral vessels Limbal vessels Major arterial circle Long posterior ciliary artery Anterior ciliary artery |
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What are the Anterior and posterior scleral foramen filled by? |
Anterior: The cornea Posterior: Lamina cribrosa of the optic nerve |
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State the layers of the Sclera including the conjunctiva and choroid from outermost to innermost |
Conjunctival epithelium Conjunctival Stroma Tenons Capsule Episclera including episcleral vessels Scleral Stroma Lamina Fuscia Choroid |
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What is the function of the episclera? |
Connects sclera to Tenons Capsule |
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What is the scleral Stroma made up of and why is it arranged this way? |
Irregularly arranged collagen Scatters light giving a white appearance |
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State 3 functions of the scleral Stroma? |
Mechanical strength Protection Attachment for extrinsic ocular muscles |
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Why does the Lamina fusca have a darker appearance? |
Higher concentration of melanocytes |
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What is the function of the lamia fusca? |
To provide a route for the blood vessels and nerve |
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What is the nerve supply anteriorly and Posteriorly for the Sclera and which cranial nerve do these feed back into? |
Anterior: 2 long posterior ciliary nerves Posteriorly: short posterior ciliary nerves They feed back into the Opthalmic division of thr trigeminal nerve (Cranial Nerve V) |
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What is the blood supply for the Sclera: At the limbus Posteriorly |
At the limbus: anterior ciliary vessels Posteriorly: vessels branching from the circle of Haller-Zinn around the optic nerve head |
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With age, the Sclera can take on a blue/grey appearance, why is this? |
Age related thinning or a change in water content |
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Identify the 3 anatomical planes of this diagram. |
A: Horizontal B: Coronal C: Saggital |
