Cornea Vol. 2 Flashcards
What is the refractive index of the cornea?
1.376
What is the average radius curvature of the central cornea?
7.8 mm
What is the average power of the cornea in diopters?
43 D
What is the average total power of the human eye in diopters?
59 D
What is the major source of astigmatism in the optical system?
Cornea
What type of epithelium composes the corneal epithelium?
Stratified squamous epithelium
How thick is the corneal epithelium?
0.05 mm
What percentage of the total corneal thickness does the corneal epithelium constitute?
Approx. 5%
What structures of the corneal epithelium prevent penetration of the tear fluid into the stroma.?
Tight junctions
What type of collagen makes up the basement membrane of the corneal epithelium?
Type IV collagen
What types of collagen are found in the corneal stroma?
Types I, V, and VI
What are two major proteoglycans found in the corneal stroma?
Decorin and lumican
How does the refractive index of the cornea change from anterior to posterior?
Decreases from anterior to posterior
What is the normal percentage of water content of the corneal stroma?
78%
What creates the swelling pressure of the corneal stroma?
Negatively charged proteoglycans proteoglycans that repel each other
Where is the density of keratocytes in the corneal stroma the highest?
Anterior stroma
How thick is Descemet’s membrane at birth?
3 um
How thick Is Deseret’s membrane In the adult?
10 to 12 um
How do radial incisions change the shape of the cornea?
Radial incisions cause flattening in the meridian of the incision and flattening 90 degrees away
How do tangential incisions change the shape of the cornea?
Tangential incisions cause flattening of the meridian of the incision and steepening 90 degrees away
What factor does the effect of incisional surgery greatly depend on?
Hydration of the corneal stroma
What can occur to the refractive error of a patient exposed to high altitude or low P02?
Hyperopic shift
What type of diurnal shift can occur in patient following radial keratotomy due to stromal swelling?
Hyperopic shift in the morning
What optical characteristic of the cornea makes sclerotic scatter possible?
Total internal reflection
