9- Corneal Function Flashcards
What is the primary function of the cornea
To refract light
What are some factors that affect refraction
- Curvature of anterior surface
- change in refractive index from air to cornea
- corneal thickness
- curvature of the posterior surface
- change in refractive index from cornea to aqueous
What is the approximate power of the eye
60 D
What is the power of the cornea
40-48 D
What is the 2nd primary function of the eye
To transmit light
How do you want the eye to transmit light
Minimal scattering
Minimal distortion
Maximum transmission
What are some factors that help to maximize the light transmission
- Smooth optical surface
- Regularly of surface epithelial cells
- Absence of blood vessels
- Arrangements of correct partial arrangement of collagen fibrils in stroma
- Less than 1% light scatter
How does the cornea act to protect your long term vision
Minimize risk of infection
Prevent damage to retina
Avoid penetration injury
Swift healing
T/F the cornea is densely innervated
True
What is the cornea cornea sensitive to
Touch, temperature (especially cold), and chemicals
When you touch the cornea what happens
Involuntary lid closure
Corneal blink reflex (In on 5 out on 7)
What is the normal CV of the corneal endothelium
0.25
Stroma makes up what percent of the cornea
90%
When is corneal transparency optimal
When the stroma is 75-80% water
Lack of these structures helps maintain the transparency of the cornea
Blood vessels
Lymph vessels
Myelin sheaths
What is Bowman’s Layer composed of?
Collagen and laminin
PRK surgery destroys what layer of the cornea
Bowman’s layer
Bowman’s layer is resistant to this (3)
Deformation
Trauma
Foreign bodies
What is Dua’s layer?
The 6th layer of the cornea
T/F Dua’s layer is able to withstand high pressures
True
What cellular linkages held the epithelium together
Epithelium
What cellular linkage holds the stroma together
An ionic proteoglycans that pull water in
This layer of the cornea slowly leaks fluids into the cornea and stroma
Endothelium
What is corneal hydration dependent on?
- Barrier function of epithelium and endothelium
- Anionic characteristics of molecules in stroma
- Water and ion transport in epithelial and endothelial cells
What is the movement of water out of the cornea mediated by?
Ion flow and osmotic gradients
What molecules are the major driving force for water transport across the epithelium and endothelium
Cl and Na
What is Phthisis bulbs
A shrunken eye
What are aquaporins
Small integral membrane proteins that reside in the plasma membrane
If IOP is very high in the eye the cornea will take on what look
Cloudy
What is a corneal abrasion
A minor abrasion of the epithelium that causes a loss of the zonular occludens
Most of the oxygen fro the cornea comes from this
Air
What does healing of the cornea rely on?
Peptide growth factors
T/F the cornea is the fastest healing tissue in the body
True
How long does it take for the cornea to heal?
24-48 hours
How long does it take to replace the corneal epithelium
2 weeks
What consumes the most oxygen: endothelium, epithelium, or stroma?
Endothelium and epithelium
T/F the epithelium can store glycogen
True
What is a corneal ulcer
Inflammation of infection that compromises the integrity of the epithelium
Are the epi/endothelium hydrophobic or hydrophillic?
Hydrophobic
What layer of the cornea has a high water content
Stroma
What layer is impermeable to ions
Epithelium
What are some conditions that cause loss of stability and structure in the cornea
Keratoconus
Ectasia
High/low pressure
