wk 3 (L3 cornea)

what is the cornea

• clear dome shaped covering that covers the iris + pupil

• occupies 1/6 of the globe area

5 layers of the cornea

“Every Bad Sassy Dad Eats”

From front to back:

1. Epithelium – outer protective layer.

2. Bowman’s layer – tough layer between epithelium + stroma

3. Stroma – thickest layer, mostly collagen for strength and transparency.

4. Descemet’s membrane – thin basement protective layer.

5. Endothelium – innermost layer, pumps out excess fluid to keep cornea clear.

what is the transitional region where the cornea merges with the sclera/ conjunctiva

limbus

what is the central thickness of the cornea

550 um (microns)

thickness of cornea peripherally ?

700 um (microns)

size of central optical zone of cornea + function

• 3-4 mm

• critical for image formation

what type of epithelium is the cornea

Stratified squamous non-keratinized epithelium

how thick is the human corneal epithelium

50-60 um (microns)

what are the 3 layers of Corneal epithelium (top layer of the cornea)

“Spicy Wings Bravo!”

• Superficial (squamous) cells – top

• Wing cells – middle

• Basal (columnar) cells – deepes

top layer of the corneal epithelium (top layer of cornea) function + name

• superficial squamous cells

• 2-3 layers thick

• stick together using desmosomes

• outer surface of microvilli + microplicae (ridges) that help the tear film stick

• As the cells age, they loosen and fall off into the tear film, making way for new cells.'

✅ Basically: superficial cells are super flat they protect, hold tears, and naturally shed when old.

middle layer of the corneal epithelium (top layer of cornea) function + name

• wing cells (wing shaped)

• 2-3 layers below superficial squamous cells

• cells are not as flat as the surface cells above them

✅ In simple terms:
Wing cells are the middle cells in the corneal epithelium that are shaped like wings and work together closely to help move new cells up toward the surface securely and efficiently.

bottom layer of the corneal epithelium (top layer of cornea) function + name

• basal columnar cells

• single layer of tall columnar cells

• They are held firmly to the basement membrane by special anchoring structures (like hemidesmosomes).

key idea:

• Basal cells are the bottom “engine room” cells of the corneal epithelium — they divide to make new cells, stick together, and anchor the epithelium to underlying tissue so the surface stays intact and can renew itself.

corneal epithelium turn over time?

every 10 days

• (entire surface layer of the corneal epithelium is completely renewed roughly every 7-10 days in a healthy eye.)

what’s the XYZ hypothesis in corneal epithelium turn over

New corneal stem cells are produced limbus (X), move across the cornea (Y), and replace cells that are lost at the surface (Z)

what is the Bowmans layer

werf

• below last layer of the corneal epithelium (basal cells)

• acellular (without cells) layer made of collagen

• strong, protective “lasagne sheet” under the epithelium that helps keep the cornea smooth and intact

what is the corneal stroma

• Lies beneath Bowman’s layer and above Descemet’s membrane.

• mostly water and collagen arranged into lamellae

• makes up 90% of corneal thickness

• dense regular connective tissue

• Contains keratocytes (special cells that maintain the collagen and extracellular matrix).

4 core proteoglycan proteins

1. decorin

2. lumincan

3. keratocan

4. mimican

2 types of glycosaminoglycans in the cornea + explanations

1. keratan sulfate (higher water affinity// water-loving)

2. dermatan sulfate (holds water loving)

• ratio of both differs anterior compared to posterior

• keratan (top of stroma under Bowmans membrane) = pressed sponge (loves water but can’t hold much)

• dermatan (bottom of stroma above Descemet’s membrane) = loose sponge (hold more water)

purpose of more dermatan sulfate in anterior of corneal stroma vs less in posterior

• prevent water evaporation from cornea

• as it can damage the

2 layers of Descemet’s membrane

• anterior lamina

• posterior lamina

where does the descement’s membrane end

• it ends abruptly at the limbus

• in a thickened area of collagen called

• schwalbe’s line

what’s the corneal endothelium

• layer of the cornea

• next to anterior chamber + interacting with aqueous humor

• hexagonal

• cells do not replenish

why is the cornea clear

• because light is not scattered

• even keratocyte spacing

• no blood vessels

• endothelial fluid pump (water is controlled)

where does cornea get nutrients

• diffusion from aqueous humour + limbal vessels

when eyes are closed what supplies oxygen to cornea

palpebral conjunctiva

what is corneal neovascularisation

• the cornea is normally avascular (no blood vessels)

• corneal neovascularisation: when blood vessels grow on cornea it scatters light = blurry vision

• causes: hypoxia (overhearing contacts), infection, trauma, chronic dryness

key points of corneal nerves

• super sensitive

• lots of nerves form a network

• can lose sensitivity over time eg. contacts

what structures make up the uvea?

• iris

• ciliary body

• choroid

what’s anterior uveitis

inflammation of the front part of the uvea