Cornea I - Week 7

what is the cornea

transparent, avascular connective tissue with a smooth surface

the cornea is the main structural barrier to?

infections

cornea is continuous with?

conjunctiva and sclera

what fraction does the cornea provide total refractive power

2/3

refractive power of cornea

43 dioptres

refractive index 1.33

anterior surface is ____ and ______

convex and elliptical

horizontal diamter

11-12mm

vertical diameter

10.6mm

cornea is p____

prolate (stepper centrally, flatter peripherally)

how many structures in cornea

5

name the 3 main cell types cornea has

epithelial, stromal keratocytes and endothelial cells

corneal epithelium is comprised of?

flattened superficial squamous cells, intermediate wing cells and innermost cuboidal basal cells

squamous cells surfaces have small projections known as?

microplicae

where is mucin from

goblet cells

what does mucin coat and form?

coats the microplicae and forms the innermost layer of the tear film

what does the tear film do

smooths out epithelial micro-irregularities

epithelial cells are crucial in maintaining?

a stable tear film

mucin changes it from ____________ to _______________

hydrophobic to hydrophilic

what is epithelial glycocalyx

maintains ocular surface barrier function

as basal cells divide and migrate anteriorally, they change into?

wing cells

what does migrated basal cells become

squamous cells which desquamate

how many days does basal to squamous differentiation take

10 days

superficial squamous cells are linked by?

anchoring junctions (zonula occludens or tight junctions)

whats the benefit of superficial squamous cells being linked by anchoring junctions

prevent tear film inflow

wing and basal cells are connected by?

anchoring junctions (desmosomes)

basal cells are attached to BM by?

hemidesmosomes

plasma membrane of the surface epithelial cells secretes a?

glycocalyx component which binds mucin onto the corneai

intracellular junctions of the corneal epithelium are part of _______ against pathogens and allergences

1st line of protection

how many types of junctions does the cornea have

4naa

name the 4 cornea junctions

1. tight junctions (zonula occludens)

2. desmosomes

3. adherens junctions

4. gap junctions

where does the 4 junctions of the cornea exist

different depths of the stratified epithelia

describe the bowmans layer

smooth, acellular, non regenerating layer

bowmans layer contains what type of sheet

dense fibrous of randomly arranged collagen fibrils

collagen fibrils are not ordered into?

bundles

what does bowmans layer help

cornea maintain its shape

stroma is composed of?

collagen fibrils, keratocytes and extracellular “ground substances”

uniform collagen fibres run parallel to each other to form?

bundles (lamellae)

transparency is due to?

precise organisation of the stromal fibres and extracellular matrix

in the stroma, periphery is thicker or thinner at centre?

thicker

highly organised network reduces?

forwards light scatter, contributing to both the transparency and mechanical strength of cornea

what is stromal collagen fibrils

type I collagen in a complex with type V collagenke

keratocyte synthesise what?

collagen and glycosaminoglycans

why is keratocytes synthesising collgen and glycosaminoglycans crucial

maintaining ECM homeostasis

where are most keratocytes located

anterior stroma, and contain corneal crystallins

what does excessive cell death of keratocytes lead to

keratoconus

how are fibrils arranged

in sheets

how many keratocytes in normal stroma

4 million

describe descemets membrane

latticework o collagen fibrils produced by endotheliumw

what does descemet’s membrane form

the BM of endothelium

where does descemets membrane end

limbus (called shwalbe line)

describe endothelium

innermost layer of cornea, single layer of hexagonal cells. cell do not replicate or divide

cells are very ___________ active in endothelium

metabolically

epithelium is from?

surface ectoderm (between 5-6 weeks)

bowmans membrane and stroma is from?

mesenchymestroma

stroma is from?

neural crest (7 weeks)

endothelium is from?

neural crest

descemets membrane is synthesised by?

endothelial cellsname the

name the layers in order from outermost

1. epithelium

2. bowman’s layer

3. stroma

4. descemet’s membrane

5. endothelium