Cornea Lecture Notes Review

Flashcards about the cornea

The _ is the transparent, avascular structure that makes up the anterior 1/6th of the eyeball.

Transparent, avascular structure makes up anterior 1/6th of eyeball

The cornea functions in and .

Protection and optical

The average corneal diameter is horizontally and vertically.

Horizontal 11.7 mm, Vertical 10.6 mm

The anterior central radius of curvature of the cornea is .

7.8mm (~48.2 D)

The cornea is aspheric, meaning it is in the periphery.

Flatter

In young adult subjects, the is commonly steeper than the (WTR astigmatism).

Vertical meridian steeper than horizontal

In older adult subjects, the is commonly steeper than the (ATR astigmatism).

Horizontal meridian steeper than vertical

The posterior central radius of curvature for the cornea is .

6.5mm (~-6.2 D)

The central corneal thickness is .

0.536 mm (0.47-0.59 mm)

The peripheral corneal thickness is approximately .

0.67mm

The cornea is thickest in the .

Early morning

Overnight corneal swelling is approximately .

~5%

In the early morning, the anterior curvature of the cornea is and the posterior curvature is .

Anterior curvature flattest, Posterior curvature steeper

Examples of variations in normal corneal shape and thickness include and .

Keratoconus, Pellucid marginal degeneration

The microscopic anatomy of the cornea includes the , , , , , and .

Epithelium, Anterior limiting lamina (Bowman’s layer), Stroma, Pre-Descemet’s Layer, Posterior limiting lamina (Descemet’s membrane), Endothelium

The corneal epithelium has a thickness of .

50-60 μm

The corneal epithelium is .

Stratified non-keratinised

The corneal epithelium is layers thick.

5-6

The corneal epithelium is thicker at the (~ 10 cells).

Limbus

The corneal epithelium forms a permeability barrier to , , and .

Water, ions, and pathogens

The three distinct cell types of the corneal epithelium are , , and .

Squamous cells, Wing cells, Basal (columnar) cells

Squamous cells are the .

Superficial cell layers

Squamous cells consist of layers of flattened cells.

2-3

Squamous cells have near the apical surface.

Tight junctions (Zonula occludens)

Squamous cells interact with .

Tears

Two structures found on squamous cells are and .

Microvilli, Microplicae

Wing cells are the layers of cells.

Intermediate

Wing cells consist of layers of cells.

2-3

Wing cells have an and a .

Irregular shape, concave inferior surface with lateral extensions (wings)

Basal cells are the .

Innermost, single layer columnar cells

The basal cell layer is the of the cornea.

Germinative layer

Cells of the basal cell layer exhibit .

Mitotic activity

New cells are produced by .

Mitosis

As cells migrate from the basal layer to the surface, they transform from to .

Columnar to squamous

are junctions between adjoining squamous cells.

Tight Junctions

Tight junctions act as a barrier to .

Intercellular movement of substances

are prominent infoldings with adjacent cells.

Interdigitations

Interdigitations provide strong .

Intercellular adhesions

provide adhesion between adjacent cells.

Desmosomes

attach basal cells to the underlying basement membrane and anterior stroma.

Hemidesmosomes

allow for intercellular metabolic coupling.

Gap junctions

The basement membrane is the of the epithelium synthesized and secreted by basal epithelial cells.

Basal lamina

The thickness of the basement membrane is .

0.5 – 1.0 μm

The anterior limiting lamina (Bowman’s layer) has a thickness of .

8-14 μm

Bowman's layer is an region.

Acellular

The stroma makes up approximately of corneal thickness.

90%

Flattened fibroblast cells that lie between stromal lamellae are called .

Keratocytes

Pre-Descemet’s Layer (Dua’s Layer) is a region of posterior stroma adjacent to .

Descemet's Membrane

Descemet’s Membrane is secreted by .

Endothelial cells

The endothelium is a of squamous cells, lining the posterior cornea.

Monolayer