Intro to Cornea and Layers of the Cornea

Average HVID

11.8 mm

Average CL diameter

13-14 mm

Prolate

steeper in center, flatter in periphery

Oblate

flatter in center, steeper in periphery

What conditions are associated with a prolate corneal shape?

Normal, keratoconus

What conditions are associated with an oblate corneal shape?

Post LASIK or Post RK

What is the average power of the eye?

60D

What is the average power of the cornea?

45D

What is the average power of the lens?

20D

Which is not a function of the cornea?

Support for surrounding tissues

How thick is the cornea at the center?

530 μm

How thick is the cornea at the limbus?

710 μm

A thick cornea may present with a ______ IOP.

artificially high

A thin cornea may present with a ______ IOP.

artificially low

A larger radius will be ________.

less curved

If the vertical line is steeper, the astigmatism is….

with the rule

Regular vs Irregular Astigmatism

Principal meridians are 90 degrees apart

What is a fleischer ring?

iron deposits at the base of cone

What is ectasia?

thinning of the cornea

Name the finding.

Fleischer Ring

Name the finding.

Fleischer Ring

Name the finding.

Vogt’s Striae

Name the finding.

Corneal Scarring

Name the finding

Keratoconus

Name the finding.

Regular Astigmatism

Name the finding.

Irregular Astigmatism

Sometimes found following PKP (penetrating keratoplasty)

Irregular Astigmatism

What is the correct order of the corneal layers?

a) Endothelium

b) Epithelium

c) Stroma

d) Bowman’s Layer

e) Descemet’s Membrane

b, d, c, e, a

Which is not a layer of the Corneal Epithelium?

Medial Cells

How thick is the corneal epithelium?

50 microns

How many layers are the superficial cells of corneal epithelium typically?

2 cells

Superficial cells of the corneal epithelium are…

squamous

Superficial Cells of the corneal epithelium ________ keratinized.

are not usually

When might superficial cells of the corneal epithelium become keratinized?

Vit. A deficiency

Which cells have microvilli and microplicae to increase surface area and assist tear movement?

Superficial cells

Which cells secrete the corneal glycocalyx?

surface cells

Glycolcalyx confers ________ properties on the anterior surface of cells.

hydrophilic

What percent water is the cornea?

78%

What do superficial cells of the corneal epithelium use to protect the eye from invasion, regulate fluid, and prevent excess fluid uptake?

Tight Junctions

Surface cells of corneal epithelium are replaced by _______ after they slough off into the tear film.

wing cells

Wing cells are…

2-3 layers

Basal Cells are…

1 layer

Mitosis occurs in the…

basal cell layer

What adheres the basal cells to the basement membrane?

hemidesmosomes

The anchoring fibrils that make up the hemidesmosomes are what type of collagen?

VII

In the stroma, the anchoring fibrils form anchoring plaques with….

TI Collagen

Corneal Stem Cells for the basal epithelium are located…

in the 1mm band around the limbus

Turn over time for the entire corneal epithelium is about…

7 days

Bowman’s layer is about…

10 microns

Bowman’s layer is made of…

collagen fibrils and proteoglycans

Which layer accounts for 90% of the thickness of the cornea?

stroma

Where does the peripheral portion of the stroma connect?

anterior sclera at limbus

What does the stroma contain?

Collagen, keratocytes, ground substance

Lamellae

flat bundles of collagen fibrils