Corneal Function Flashcards
What are the primary functions of the cornea?
- refract light
- transmit light
- protects the internal parts of the eye
- –fast healing
- –minimize infection
- –avoid injury/damage
What are the factors that affect refraction?
- curvature of the anterior surface
- curvature of the posterior surface
- corneal thickness
- change in refractive index from air to cornea
- change in refractive index from cornea to aqueous
What is the total power of the eye?
~60D
What is the power of the cornea?
~40-48D
The cornea is __ the power of the eye
2/3 to 3/4
We want ___scattering, _____ distortion, and ___ transmission
- decreased scattering
- minimal distortion
- maximal transmission
What are the 5 keys to maximize light transmission?
- smooth optical surface
- regular surface of epithelial cells
- absence of blood vessels
- correct spatial arrangement of collagen fibrils in the stroma
- less than 1% light scatter
T/F: the cornea is one of the most sensitive tissues in the body
True
Where is the cornea most densely innervated?
The center
What nerve supplies the cornea?
Ophthalmic division of the trigeminal nerve
What is the normal CV of endothelium?
0.25
What shape of endothelial cells?
Hexagonal
T/F: endothelial cells grow back
False. Once they are gone, they are gone
The stroma makes up ___%of the cornea
90%
What is the regular size of collagen fibrils and the spacing?
And why is this important
Size: 300A
Spacing: 550A
Important for corneal transparency
The corneal transparency is optimal when the stroma is ____ water
75%-80%
Tough layer of collagen and laminin that protects the underlying layers
Bowmans layer
In PRK what layer do you destroy?
Bowmans layer
What type of junctions does corneal epithelium have?
Tight junctions
This layer has anionic proteoglycans that pull water in
Stroma
This layer of the cornea slowly leaks fluid into the cornea
Endothelium
Corneal hydration is dependent on?
- barrier function of epithelium and endothelium
- anionic characteristics
- water and ion transport
What are the major driving forces or water transport across epithelium and endothelium?
Cl- extrusion and Na absorption
Small integral membrane proteins residing in the plasma membrane
Aquaporins
What are some roles of aquaporins?
- channels
- cellular processes
- cel migration
What does high IOP do to water?
It can move excessive water into the stroma from the anterior chamber and overwhelm the endothelial transport system
A minor abrasion of the epithelium causes the loss of?
Zonular occludens
What are 2 results of a corneal abrasion?
- edema
- haziness
What does an epithelial edema do to VA?
Decreases VA
When do corneal abrasion often heal?
24-48 hours
When can epithelium be replaced?
In 2 weeks
What are the 3 required nutrients of the cornea?
- oxygen
- glucose
- glycogen
The endothelium and endothelial consumes most of what nutrient?
Oxygen
Inflammatory or infective condition that compromises the integrity of the epithelium.
Corneal ulcer
Are the epithelium and endothelium hydrophobic or philic?
Hydrophobic
T/F: epithelium is impermeable to ions
True
T/F: lipid soluble materials can generally penetrate the cornea more easily
True
Are the nerves in the cornea Myleinated or non?
Non myelinated
As we get older how will this affect our CV?
The CV will increase because of the differences between the cells that die off
