Ocular Physiology - Cornea: Midterm 1

Specular reflection is a type of reflection that occurs when light hits a smooth surface and bounces off at the same angle. In the context of viewing the endothelium of the cornea, specular reflection refers to the reflection of light off the smooth surface of the endothelium. This reflection allows for clear visualization of the endothelium and its characteristics. Therefore, the statement "You view the endothelium of the cornea with specular reflection" is true.

Na+fluorescein is a fluorescent dye that is commonly used to assess cellular damage. When cells are damaged, their membrane integrity is compromised, allowing the dye to enter the cells. Therefore, if Na+fluorescein is taken up by damaged epithelial cells, it indicates that the cells have been damaged. Hence, the statement "Na+fluorescein is taken up by damaged epithelial cells" is true.

Desmosomes are cell junctions that provide strong adhesion between cells. They consist of proteins that link the cytoskeletons of adjacent cells together. This adhesion helps to prevent the flow of substances between cells, maintaining the integrity and stability of tissues. Therefore, the statement that desmosomes help to prevent the flow of substances between cells is true.

Fluid transport in the cornea requires Na+, Cl- and HCO3- because these ions play important roles in maintaining the osmotic balance and pH regulation in the cornea. Na+ helps in the active transport of fluid across the corneal endothelium, while Cl- and HCO3- ions are involved in maintaining the electrochemical balance and pH of the corneal stroma. Without these ions, the fluid transport mechanism in the cornea would be disrupted, leading to imbalances in fluid volume and pH, which can affect corneal transparency and function.

In collagen fibrils, small particles of light can scatter. This means that when light passes through collagen fibrils, it can be deflected or redirected in different directions due to the scattering effect caused by the particles. Therefore, it is theoretically possible for small particle light to scatter at every collagen fibril.

Option B: for the basement membrane of the epithelium
Option C: Refers to the stroma
Option D: refers to the endothelium

The explanation for the given correct answer is that both the epi and endo pump water, but the majority of the water pumping, specifically greater than 90%, is provided by the endothelium. Therefore, if the endothelium is blocked, it essentially eliminates fluid transport. This supports the statement that the answer is true.

Adding water to the stroma of a plant only increases its thickness and not its diameter. This means that the overall size of the stroma remains the same, but it becomes thicker.

To calculate the flow across the tissue for a given pressure, you need to know the flow conductivity, which determines how easily fluid can flow through the tissue. Additionally, you need to know the thickness of the tissue, as this affects the resistance to flow. Finally, the area of the tissue is also required, as it determines the overall flow capacity. Therefore, all of the options A, B, and C are necessary to calculate the flow across the tissue for a given pressure.

A tight junction is a type of intercellular junction where two adjacent cell membranes fuse together, forming a barrier that prevents the passage of molecules and ions between the cells. This barrier is important for maintaining the integrity and selective permeability of tissues. The statement that only carbon dioxide, O2, and small ions can pass through a tight junction is true because these molecules are small enough to pass through the tight junction's narrow channels, while larger molecules and ions are unable to do so.

Darcy's law of bulk flow is a principle in fluid dynamics that relates the flow rate of a fluid through a porous medium to the pressure difference across the medium. In the context of the question, it implies that Darcy's law can be used to determine the amount of water that flows through the cornea, which is the clear front surface of the eye. Therefore, the statement is true.

The statement is true because the corneal endothelium and epithelium are the only layers of cells in the cornea that have tight junctions. Tight junctions are specialized connections between cells that form a barrier, preventing substances from passing between the cells. This barrier function is important for maintaining the transparency and integrity of the cornea. Other layers of the cornea, such as the stroma and Bowman's layer, do not have tight junctions.

Gap junctions allow for the passage of ions b/t cells, connecting wing cells and basal cells

Option C : refers to absorption

The cornea is not the major refractive element of the eye. It only contributes about 40D to the total refractive power of the eye. The corneal curvature and axial length do determine the power of the eye. Cataract surgery was not the first type of refractive surgery, it is a procedure to remove a cloudy lens. Damage to the corneal endothelium during RK (Radial Keratotomy) is a major problem, not a minor one. In the LASIK procedure, the epithelial layer is not completely removed, only a flap is created. However, in PRK (Photorefractive Keratectomy), the epithelial layer is completely removed.

The Pump-leak Hypothesis suggests that the maintenance of stromal hydration and transparency is achieved through a balance between active fluid transport (pumping) and passive fluid movement (leakage) in the stroma. This hypothesis proposes that the endothelial cells of the cornea actively pump fluid out of the stroma, while the epithelial cells create a barrier to prevent excessive leakage. This balance is crucial for maintaining the proper hydration levels and transparency of the cornea.

Also air-tear interface, endothelium - aqueous

Keratin is hydrophobic, would not want that on the cornea

The perfect lattice hypothesis suggests that destructive interference occurs in Maurice, which supports statement A. Statement C is supported by Benedek and Farrell's statement that destructive interference predominates when the average number of fibrils in an area does not fluctuate greatly from the overall average. Statement D is supported by the fact that in the sclera, collagen fibrils vary in size and concentration. Statement B is not supported as there is no mention of perfect lattices being found on electron micrographs.

The stroma does not swell parallel to its surface; instead, it swells perpendicular to its surface. Collagen fibrils do not pull water into the cell; they provide structural support to the tissue. Therefore, these statements are false.