Lecture 14 Cornea Physiology

how much of the total body weight is total body water (TBW)

60%

how much of the total body weight is intracellular fluid (ICF)

40%

how much of the total body body is extracellular fluid (ECF)

20%

20% of body weight is extracellular fluid (ECF), what does this include

plasma and interstitial fluid

what is the resting membrane potential of a typical non-excited cell or neuron

-50 to -75 mV

what does the cell membrane do

Creates separation between ECF vs. ICF which create fluid compartments

Regulates ECF – ICF exchange

Allows for communication

Provides structural support for cell and tissues

two types of transport for substances to move across a cell's plasma membrane

passive transport and active transport

which type of transport require no energy or ATP

passive transport

which type of transport require energy or ATP

active transport

define simple diffusion

Movement of small, non-polar molecules (like O₂ and CO₂) directly through the lipid bilayer. No protein is needed.

define Facilitated Diffusion (Protein-Mediated)

Movement of polar or large molecules down their gradient using specific membrane proteins.

functions of channels or pores in facilitated diffusion (protein-mediated)

they allow for fast and selective passage. They can be "gated" (open/close).

two types of channels in passive transport

channel or carrier mediated

examples of channels or pores in Facilitated Diffusion (Protein-Mediated)

aquaporins for water or ion channels

what are carrier proteins in Facilitated Diffusion (Protein-Mediated)

membrane-embedded proteins (sometimes called "transporters") that bind a molecule, change shape, and release it on the other side.

what are Active Transport Pumps & Carriers

Specific membrane proteins that act as "pumps" to move ions or molecules against their natural flow.

an example of primary active transport

Na+/K+ ATPase pump in the corneal endothelium

function of Na+/K+ pump

Actively transport Na+ out of the cell and K+ into the cell against electrochemical gradients

how much Na and K are pumped per ATP molecule

3 Na+ out and 2 K+ in

what is the overall charge of the intracellular environment compared to the extracellular environment

negatively charged

describe the mechanical properties of cornea

Hierarchical structure and degree of collagen fibril cross-linking, end to end collagen fibril length (viscoelastic properties)

what is constantly pressing on the cornea in an outward direction

The static net internal pressure

what is the The static net internal pressure constantly stressing the cornea in an outward direction

intraocular pressure

what is the intraocular pressure in our eyes

16 + - 3 mmHg

which stress is more well tolerated by cornea: internal or external

internal stress

why is cornea trauma common?

because it is constantly exposed and stressed

function of Corneal topography

Measures contours/shape of corneal surface

assorted purposes of Corneal topography

Contact lens fitting

Corneal disease diagnosis and management (e.g. Keratoconus)
Refractive surgery

what technique do we use for contact lens fitting

Corneal topography

what technique do we use for Corneal disease diagnosis and management such as keratoconus

Corneal topography

what technique do we use for refractive surgery

Corneal topography

how does refractive surgery work

we measure the curvature and calculate desired result

what is Intrastromal Corneal Ring Segments (ICRS/INTACS)

a small, arc-shaped plastic or donor-tissue device surgically implanted into the mid-peripheral stroma of the cornea to reshape and flatten its central curve, and to improve vision

what is keratoconus

A progressive eye disease where the cornea thins and bulges into a cone shape.

what is Corneal refractive therapy (CRT/Orthokeratology)

a non-surgical treatment that uses specialized rigid gas-permeable contact lenses to temporarily reshape the cornea while you sleep

which wavelengths are almost entirely absorbed by the cornea

<300 nm which is th ultraviolet radiation wavelength

what explains why the cornea absorb specific wavelengths around 300 nm

due to proteins (tryptophan) and nucleic acids (ascorbic aids)

what is tryptophan in terms of absorption in the cornea

an aromatic amino acid found in corneal proteins where its residues absorb heavily in the 280–300 nm range.

why are nucleic acids responsible for absorption in the cornea

because cellular DNA and RNA have a strong absorption peak right around 260 nm

what is transmitted in our cornea

the visible spectrum (the cornea is highly transparent to visible light)

which wavelengths are more likely to be transmitted by our cornea

wavelengths above 300 nm

why is it dangerous that the cornea and the crystalline lens are largely transparent to near-infrared light

Because it passes right through the anterior structures without being stopped and can damage the retina

what does shorter wavelength mean in the optics of cornea

it signifies higher energy, so each photon (light particle) that hits your skin has more energy

why do we not get sunburn in the cornea when there are objects around us

because objects around us absorb 85% of the UV and they reflect light well so that our cornea does not absorb

why do we get sunburn in the cornea where we are in snow

because 85% of the light is reflected to our cornea instead of being absorbed by objects around us

how does the snow affect our cornea after exposure to it for a long time

the eyes feel burn/pain/redness due to cornea absorbing all the light. cell death might be activated which lead to cell loss and snow blindness

range for ultraviolet radiation

100 nm to 400 nm

range for visible radiation/light

400 nm to 800 nm

range for infrared radiation

800 nm to 1 mm

where does reflection of cornea occur

at points of refractive index (RI) change

refractive index of tear

1,33

refractive index of corneal reflex

1.376

why does reflection occur at points of refractive index (RI) change

due to a large difference in refractive index between air and tear

why is there small refractive index changes in the interfaces between layers

because there is low reflection within the cornea

what cells in cornea have more mitochondria

Endothelial cells 

what cells in cornea have less mitochondria

Corneal epithelial cells