[ODOAP] Cornea to Limbus - Midterm

Cornea

the transparent anterior one-sixth of the eyeball.

the main structure responsible for light refraction entering the eye.

Shape and Location (Cornea)

Convex and somewhat elliptical when viewed from the front, forming the anterior one-sixth of the eyeball. It is separated from the sclera by a slight groove called the sulcus sclerae.

11.7 mm

Horizontal Diameter (Cornea)

About 10.6 mm

Vertical Diameter (Cornea)

11.7 mm in diameter

Posterior (Concave and circular)

Center (Cornea)

Thinnest, about 0.5 to 0.6 mm

Periphery (Cornea)

Thicker, about 0.7 mm

7.7 mm

Anterior Surface Radius (Cornea)

6.9 mm

Posterior Surface Radius (Cornea)

1.00

refractive index of air

1.33

refractive index of aqueous humor

Anterior Epithelium
Bowman's Layer
Corneal Stroma
Descemet's Membrane
Endothelium

5 LAYERS OF CORNEA

50–60 μm thick

Thickness of Corneal Epithelium

Epithelium

The outermost layer of the cornea made of several cell layers

Stratified epithelium

Tissue made of multiple layers of cells stacked on top of each other.

Squamous cells

Flat, thin cells found on the surface layer of the cornea.

Nonkeratinized

Cells that do not form keratin (a hard, dry protein).

this keeps the cornea clear and moist.

Superficial cells

The topmost cells of the epithelium that contact the tear film.

Microvilli

Tiny finger-like projections on the cell surface that help hold the tear film.

Microplicae

Small ridges or folds on the cell surface that increase surface area for tear film attachment.

Wing cells (Middle-zone cells)

The middle layer of the epithelium; cells are polygonal (many-sided) and connect the surface to the base.

Basal cells

Deepest layer of tall column-shaped cells that constantly divide to make new surface cells.

Basement membrane

A thin supporting sheet under the basal cells that separates epithelium from stroma.

Hemidesmosomes

Tiny anchoring structures that attach basal cells to the basement membrane.

Langerhans’ cells

Immune cells that detect foreign particles; mostly found at the corneal periphery.

Polyhedral cells

Cells with many sides; characteristic shape of the middle “wing” layer.

Tear film

The thin moisture layer covering the cornea that keeps it smooth and nourished.

Bowman’s Layer (Membrane)

A tough, acellular layer of the cornea located just beneath the epithelial basement membrane.

Provides structural support and protection to the cornea; acts as a barrier to injury and infection.

Location of Bowman’s Layer

Lies immediately beneath the basement membrane of the corneal epithelium.

8–12 μm thick

Thickness of Bowman’s Layer

Composition (Bowman’s Layer)

Made of interwoven collagen fibrils embedded in intercellular substance; the collagen fibers are fine and irregularly arranged compared to the stroma.

Acellular

Cellular Content of Bowman’s Layer

Non-regenerative

Regenerative Capacity (Bowman’s Layer)