Cornea II - Week 7

definition of cornea

transparent avascular with smooth surface

where does the cornea form from

the surface ectoderm

where are the cells located that migrate into the cornea to give future cornea stroma

periocular mesenchyme

corneal epithelium

surface ectoderm

bowmans membrane

mesenchyme

stroma

mesenchyme and neural crest

descemets membrane

synthesised by endothelium

endothelium

neural crest

where do neural crest derived cells invade space, and what is produced?

between the epithelium and endothelium to proudce hyaluronan rich ECM

what do cells become once they invade space

keratocytes, which replace hyaluronan rich ECM with a collagen fibril/PG rich ECM

how would the cornea structure be described

most densely innervated

what do corneal nerve endings provide

sensations of touch, pain, and temperature

what 2 things washes objects from the cornea

reflex blinking and lacrimation

definition of transparency

having the property of transmitting light without appreciable scattering, so that bodies lying beyond are seen clearly

name the 4 structural factors important for transparency

1. arrangement of stromal lamellae

2. uniform arrangement of epithelium

3. avascularity

4. relative state of hydration

definition for stroma

highly organised network which reduces forward light scatter, contributing to cornea’s transparency & mechanical strength

name the biochemical composition for the stroma

H20, collagen, other proteins

in corneal pathologies, changes in 1 or more layers can lead to?

increased light scattering and transparency loss

name the 3 main compartments for stroma

collagens, proteoglycans (PG’s), and keratocytes

collagen is laid down with what?

lamellae

describe the packaging of lamellae in central corneal stroma

packaging density is higher in anterior lamella than in posterior ones

posterior stroma can ______ more easily than anterior

swell

describe stroma lamellae

bulk of corneal thickness, can regenrate

what is transparency due to

precise organisation/hydration of stromal fibrils and ECM

what are fibrils

uniform lattice pattern

stromal cells are ?

keratocytes

what do keratocytes maintain

ECM turnover synthesising collagen and PG’s

what are keratocytes vital for

maintaining corneal homeostasis

where are keratocytes located

anterior stroma and contain corneal crystallin’s, which reduces light backscatter

what does excessive cell death lead to

keratoconus

what is relative state of hydration

active transport of electrolytes out of endothelium

normal cornea maintains a state of ?

relative dehydration needed for transparency

name 3 ways of how dehydration is maintained

1. stromal swelling pressure

2. barrier functions of epithelium and endothelium

3. active pumping action of endothelium

what does the sodium potassium pump cause extrusion of

Na+ and H20 from stroma

where are the sodium potassium pumps located

in endothelial cell membranes

what is the primary function of endothelium

permit ‘leakage’ of solutes and nutrients from aqueous humour to more corneal layers

how does the nutrients of corneal epithelium

diffusion of glucose

where does the endothelium transport H20 from and to

from the stromal facing surface to the aqueous facing surface

what is crucial in endothelium pump mechanism

Na+/K+ATPase and carbonic anhydrase

the endothelium actively dehydrates what?

the stroma through the action of water pumps in the endothelium

what is the corneal endothelium responsible for

maintaining the hydration of cornea, via active transport of various ions

what happens if the cornea swells much above its physiological hydration

it scatters light and loses transparency

endothelium based pumping mechanism maintains what

corneal hydration

what happens when pumping mechanism fails and cornea swells

regions without collagen fibrils impair corneal transparency

name 3 causes of oedema (eyesight)

• CL wear

• glaucoma

• ageing

name 3 reasons why oedema may be caused

temperature change, pH, hypoxia

what areas without fibrils called

lakes

deeper layers are more ____ ________ than superficial layers?

strictly organised

corneal stroma swells how much more than scleral stroma when immersed in physiological saline

2.5X

how is corneal thickness measured

pachymeter

what is the average corneal thickness

0.535 mm

what is the average anterior corneal curvature

7.8 mm

describe the blood supply in the cornea

avascular, small loops derived from anterior ciliary vessels, no lymphatics

loops are not actually in cornea but in________ _______?

subconjunctival tissue

name the 3 things the cornea needs energy for

• metabolism

• transparency

  • dehydration

how is energy provided for the corneal

glucose, amino acids, vitamins

02 comes mainly from atmosphere, followed by _______ ______

aqueous humour