Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

APCO > CL Sequencing Physiology > Flashcards

CL Sequencing Physiology Flashcards

1
Q

Why are central K readings misleading indicators of overall corneal topography?

A

Because cornea should be spherical which is not the case.

It tells you central is 4mm only, nothing about spherical

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q
  1. Is the cornea symmetrical?

2. The curvature flattens towards which part of the cornea?

A
  1. Not symmetrical

2. Periphery

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the normal HVID?

A

~12mm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the 4 topographic zones?

A
  1. Central (4mm spherical)
  2. Paracentral (~ diameter of scotopic pupil)
  3. Peripheral (flattest and aspheric)
  4. Limbal
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Cornea provides how much refractive power of the eye?

A

2/3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Why is cornea curved, transparent with clear optics?

A

It all thanks to cellular organisation and the air TF interface

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Slight irregularities can be compensated by?

A

Overlying TF

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What allows cornea to withstand shear forces of blinking, EM, microbial infection and FB?

A
  • cell specialisation
  • cell turnover
  • tight junctions
  • surface glycocalyx
  • TF
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How many layers does cornea have? What are they?

A

5 layers!

  1. Epithelium
  2. BOwman’s layer
  3. Stroma
  4. Descemet’s membrane
  5. Endothelium
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

How many cells does epithelium have? What are they?

A

3 cell types!

  1. Basal cells
  2. Wing cells
  3. Squamous cells
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Microplicae and microvilli on the epithelium surface play a role in TF by doing what?

A

Anchoring the mucus layer (glycocalyx)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How long is cell shedding and turnover (basal to the surface) without CL wear?

A

~7 days

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Does epithelium negatively or positively impacted by CL wear?

A

NEGATIVE!

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Epithelium is a permeability barrier to what?

Adjacent cells are connected by what?

A
  1. water
  2. ions
  3. most hydrophilic molecules (eg. fluorescein)
  4. infective pathogens through tight junctions (desmosomes)
  5. Aquaporins (water channels)
  6. Gap junctions (ion transport)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

In the stroma, how do intermediate filaments in the cytoskeleton are linked through?

A

Linked through the hemidesmosomes via anchoring fibrils to anchoring plaques

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

CL wear can reduce the epithelial barrier function related to what?

A
  1. Hypoxia dose

2. Overnight wear

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How thick is the stroma and it is how many % of the cornea?

A

Thickness: 0.50mm thick/ 500 microns

It is 90% of the cornea

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What does stroma contain?

A

2-3% keratocytes (fibroblasts) and 1% ground substance (GAGs) interspersed between lamellae

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What are keratocytes in the stoma?

A

They are:

  • thin
  • flat cells
  • tight junctions
  • 10 microns in diameter with long processes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What are GAGs in the stroma?

A

They are:

  • proteoglycans
  • poly-ionic
  • induce water retention
  • influence fibril arrangement
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What are stromal Lamellae?

A

A regular arrangement of collagen fibrils within each lamellae provides optical clarity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What happens when there’s infection and/or irritation in stromal lamellae?

A

Leads to epithelial cells will release cytokines and chemokines to begin immune defence

23
Q

What kinds of WBC will go to the infected site in stromal lamellae?

A
  1. Limbal vasodilation
  2. Keratocyte migrate
  3. Interferon
  4. Neutrophils
  5. Natural Killer cells
  6. Macrophages
24
Q

What happens when there’s corneal insult in stromal lamellae?

A

Leads to:

  1. Disorganised spacing
  2. Oedema (Striae)
  3. Tissue loss (ulcer)
  4. Clarity loss (infiltrate + scarring)
25
What is the corneal endothelium? Do endothelial cells lost with age?
A mono-layer of squamous cells 500,000 cells at birth (4,500 cells/mm2) Yes, it loses with age
26
What does corneal endothelium have/do?
1. Inter-locking irregular edges, tight junctions, lots of organelles, metabolic activity 2. allows passage of ions and small molecules 3. Maintains osmotic gradient by metabolically driven pumping ions out of the stroma into the aqueous
27
Endothelium function
1. Pumping function: maintains 78% corneal hydration for optimal transparency & normal thickness 2. Minimal endo cell count: 1000 cells/mm2 - needed to maintain this state
28
In endothelium: | Age, pathology, trauma, oxygen deficiency (hypoxia) can lead to?
- loss of pumping ability - corneal oedema - corneal striae - polymegethism (size) - polymorphism (shape) of the cells
29
What does innervation do?
1. There's 50-80 myelinated and unmyelinated precorneal nerve trunks -> enters mid stroma -> lose myelin at the cornea and branch anterior centrally 2. Dense subepithelial plexus, unsheathed nerve endings enter the epithelium and branch out among basal cells 3. Richly innervation, initiates blink reflex, wound healing (trophic role), and tear secretion
30
What is the transition zone between cornea and conjunctiva/sclera?
1.5mm Horizontal 2mm Vertical * Surgical reference point and significant change between steeper corneal curvature and flatter sclera
31
Why do you need to respect the limbus?
Because it has a: - minor role in corneal nutrition - Important role for defence - location of limbal stem cells So... need to avoid CL touch, interaction or pressure on this area
32
Terminal arteries of limbus have distinctive looping, so what do you have to look out for?
- Engorgement - NVZ with CL wear
33
What does the cornea need to maintain tissue health and control hydration? These nutrients are supplied by what?
1. Oxygen 2. Glucose 3. Vitamins 4. Amino acids 5. Other metabolites These nutrients are supplied by (oxygen supply): 1. Peri-limbal vasculature - 55mmHg O2 tension 2. TF - 155mmHg O2 tension 3. Aqueous humour - 30-40mmHg O2 tension 4. Palpebral vasculature - 55mmHg O2 tension
34
How much is corneal influx on average?
6microlitres/cm2/hr
35
If you wear CL, it reduces or increases oxygen availability to the cornea?
REDUCES
36
What permits corneal flux through the CL?
CL oxygen permeability (Dk)
37
What is Dk? | What is Dk/t?
Dk: measures oxygen permeability of CL - means: how much oxygen is passing through the material under certain given conditions Dk/t: measures oxygen transmissibility of CL - Dk/t calculated using Dk of CL material and thickness. Usually refers to a CL with certain power ** Higher these values, better Dk/t of the material. Higher oxygen flow to the cornea and can improve comfort and longer-term tolerance * Dk/t is dependent on CL thickness * Local Dk/t is important. There's a significant impact on central and peripheral CL thickness, especially for higher powers
38
What happens to the cornea when we sleep?
5% overnight oedema (increase in corneal thickness) in NORMAL eyes is observed WITHOUT CL wear
39
What happens when there's a 5% increase in corneal hydration?
Leads to light scatter - increase water uptake of GAGs between fibrils causes fibre aggregation --> seen as striae after overnight eye closure even w/o CL wear But return to normal/ baseline within 1 hour of waking
40
Think about the impact of CL EW, or even long-day wear of low Dk/t CL on the diffusion of CO2 and O2 We all know eye closure + CL wear will reduce oxygen tension. So, low O2 tension leads to?
Build up of: 1. Lactic Acidosis 2. Increased osmotic load 3. increase water intake into cornea - --> OEDEMA! ** Long term --> tissue change
41
What are the signs you can see/ complications from CL? What are they and what causes them?
1. Corneal NVZ What are they? Causes: 2. Epithelial Microcysts What are they? Causes: 3. Corneal Striae What are they? Causes: 4. Endothelial polymegethism What are they? Causes: 5. Endothelial Blebs What are they? Causes:
42
What has a significant impact on TF flow and CL fitting, movement, insertion, and removal?
1. Lid action 2. Aperture Size 3. Gravity
43
What is a TF?
Tears: - a complex, structured, surface film secreted by lacrimal and accessory glands - which protects and nourishes the OS and provide goof optical front surface
44
What are the roles of the TF?
1. Optical: - TF maintains an optically uniform interface between the air and anterior surface of CL 2. Mechanical: - TF acts as a vehicle for the continual blink-mediated removal of intrinsic and extrinsic debris and particulate matter from the front and underneath the CL 3. Lubricant: - TF ensures a smooth movement of eyelids over the front surface of the CL, and CL over the globe, during blinking 4. Bactericidal: - TF contains defence mechanisms in the form of proteins, antibodies, phagocytotic cells, and other immunodefence mechanisms that prevent CL-induced infections. 5. Nutritional: - TF supplies epithelium with necessary supplies of oxygen, glucose, AA, and vitamins underneath CL via lid-lens tear pump 6. Waste Removal: - TF acts as intermediate reservoir for removal of corneal metabolic byproducts (CO2, lactate) from underneath the CL via lid-lens tear pump.
45
TF vs CL thickness And what are the things you should consider?
5 microns vs 100 microns *CL are highly disruptive to the TF structure Consider: - Impact of lens edge design and movement - Pre-lens TF - especially the lipid layer - Post-lens TF - tear exchange, aqueous, and mucins
46
CL-associated keratitis can result from many mechanisms like what?
1. Infection 2. Toxic solutions 3. Bacterial endotoxicity 4. Immunological rxn 5. Trauma 6. Hypoxia 7. Metabolic Disturbance Other aetiological factors: 1. Breakdown of trapped post-lens TF debris 2. Lens deposits 3. Poor px hygiene
47
What does the chemical messages in the immune cascade lead to?
1. Redness 2, Recruit inflammatory cells (WBC) into the cornea
48
Why do we avoid CL edge touch with the limbal area?
Don't want lens edge to interact with area bcoz can induce NVZ (The vessels can grow into the cornea and can leak to the stroma)
49
What are the 4 clinical signs associated with corneal hypoxia? How is corneal thickness impacted by CL wear?
1. Epithelial blebs 2. Stroma oedema 3. Polymegethism 4. Corneal striae 5. NVZ ingrowth BV in cornea
50
What are the key influences of the eyelid on CL fit?
Rotational force on CL | Push CL down and back
51
What impact does CL wear have on the corneal TF?
Highly disruptive TF, consider pre and post-lens TF, the impact of lens edge design and movement?
52
What are the functions and composition of the TF?
Lipid, aqueous and mucin | - Each of them can affect CL position, deposition differently
53
What is the immune response to corneal insult?
Breakdown of the post-lens TF debris, deposits in lens and poor px hygiene --> can cause redness, inflammatory cells into cornea

APCO (13 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions