2 Cornea Flashcards
What is the cornea
Transparent, avascular tissue
What is it’s function?
Optical(relating to action of light), structural integrity, protection
As a percentage, how much refraction power does it contribute in the eye?
70%
Whats it’s refractive power
43D
Describe the shape of the Cornea
Anterior surface is convex, posterior surface is concave Anterior surface is elliptical, Posterior surface is spherical
What are the diameters of the anterior surface of the cornea
Vertical Diameter is 10.6mm, horizontal Diameter is 11.7mm
What are the diameters of the posterior surface
11.7mm
What is the thickness of the cornea
Centre is approx 0.5mm (550 microns), peripherally is 0.7mm
What is the radius of curvature referring to
concept of an imaginary sphere that approximately matches the curve of something, the radius of the curvature will be the radius of this imaginary sphere
What is the radius of curvature for the anterior and posterior surfaces of the cornea
Anterior surface radius of curvature is 7.8mm, posterior surface is 6.5mm
What is the refractive index of the cornea vs air vs aqueous
Cornea 1.376, Air is 1, Aqueous is 1.336
How many layers of the cornea are there (and list them)
5; Epithelium, bowman’s layer, stroma, descemet’s, endothelium (with Dua’s layer between Stroma and Descemet’s)
What are the component layers of the Corneal Epithelium
4 layers: Surface Cells, Wing Cell Layer, Basal Cell Layer, Basement membrane
How thick is the epithelium
50-60 microns, with 5-6 cell layers centrally (10 cells thickness at limbus)
How long does epithelium cell turnover take
7-10 days on average, due to stem cells at limbus
What is the epithelium composed of
Non-keratinized, Stratified, squamous cells
What does “stratified” mean in this context
literally meaning many layers
what does “squamous” mean in this context
Describes the shape of the cells, i.e. flat, thin, like scales
What is the relevance of it being non-keratinized
Kertin makes the cell tough but opaque, also incidentally, not having keratin allows it to heal quickly
Describe the surface cells
2-3 cells layers that are flat in shape, have microvilli (imporant for tear film function).
What cell junction type do surface cells have
Joined together by Zonula Occludens, or tight junctions
Describe the wing cell layer
Middle 3-4 cell layers are called wing cell. Polyhedral cells with convex anterior and concave posterior surface, joined by zonula occludens to superficial layers, and desmosomes to more deep layers (zonula adherens)
Describe Basal Cells
single cell layer of tall and columnar cells that often show mitosis, interdigitating lateral walls are joined together by Descmosomes, and to the basement membrane by hemidesmosome
Describe the basement membrane
PAS positive (periodic acid schiff stain) so it will turn magenta. Firmly attached to Bowman’s layer by anchoring fibrils. This is secreted by the basal cells, composed of superficial lamina lucida, deep lamina densa
Describe Bowmans layer
thin layer, 8-14 microns thick. Acellular. A “condensation” of underlying stroma and resistant to trauma/infection but if breached leads to rapid spread of infection. Doesn’t regenerate. Contains superficial nerve plexus (just beneath it)
