Ocular Physiology - Cornea: Midterm 1

Na+fluorescein is taken up by damaged epithelial cells.

• True

• False

Desmosomes (where two cells come together) help to prevent the flow of substances b/t cells

• True

• False

Fluid transport in the cornea requires Na+, Cl- and HCO3-

• True

• False

It is theoretically possible to have small particle light scatter at every collagen fibril.

• True

• False

The epithelium: A. Has superficial cells, wing cells and basal cells B. Three types of collagen (IV, VII, XII) C. Contains MPS, keratocyes D. Is one cell layer thick with tight juntions

• A

• B

• C

• D

Both epi and endo pump water, but greater than 905 of the water pumping is provided by the endothelium. Blockingthe endothelium essentially eliminates fluid transport.

• True

• False

Water added to the stroma only adds to its thickness, not diameter

• True

• False

Which of the following do you need to know in order to calculate the flow across the tissue for a given pressure? A. Flow conductivity B. Thickness of a tissue C. Area of a tissue

• A

• B

• C

• All of the above

A tight junction is where two cell membranes  fuse together. Also only carbon dioxide, O2 and small ions through

• True

• False

Darcy's law of bulk flow tells us how much water flows through the cornea

• True

• False

Only the corneal endothelium and epithelium have tight junctions.

• True

• False

Gap junction don't allow passage b/t cells. They keep the wing cells and basal cells from becoming electrically coupled

• True

• False

What conditions must be met in order for large particle light scatter to occur? A. An interface with refractive index different from the medium. B. The interface has to be longer than 1 wavelength C. A photon must be lost and energy given off as heat.

• A

• B

• C

• A and B

• B and C

Select the FALSE statements

• The cornea is the major refractive element of the eye (+48D)

• Corneal curvature and axial length determine power of the eye Corneal curvature and axial length determine power of the eye Corneal curvature and axial length determine power of the eye

• Cataract surgery was the first type of refractive surgery

• Damage to the corneal endothelium during RK is a minor problem

• In the lasik procedure the epithelial layer is also removed completely similarly to PRK

The ___________ Hypothesis explains the maintenance of stromal hydration and for that matter transparency.

Major points of reflection include:

• Keratocytes

• Mitochondrial reflection

• Epithelium - and Bowman's interface

Select True statements regarding the corneal epithelium

• Basal cells undergo mitosis to produce wing cells

• In wing cells we see internal degradation of the organelles of the cell

• Superficial cells contain only cytoplasm and no debris

• The epithelium of the cornea in general is very different in lifecycle and characteristic from the epithelium of the skin.

• Like the epithelium of the skin, the epithelium of the cornea excretes keratin

Select TRUE statements A. Maurice - perfect lattice hypothesis gives destructive interference B. Perfect lattices are found on electron micrographs C. Benedek and Farrell  stated that the average number of fibrils in an area must not fluctuate too greatly from the overall average for destructive interference to predominate D. In the sclera the collagen fibrils range in size and concentration.

• A

• B

• C

• D

Select false statements:

• Stromal swelling pressure is the mechanical load/unit area required to maintain the tissue at a fixed water content

• Stroma swells parallel to its surface

• Collagen fibrils pull H20 into the cell

• GAGS are the origin of swelling pressure

• Swelling pressure is reduced over time in contact with aqueous solutions, GAGS lost to the solution

• Substances that precipitates GAGS decrease swell pressure

• IOP acts as external pressure