1. CL I - Intro & Physiology Flashcards
What is the typical sequence for CL trialling? (5 steps)
- Full eye test
- CLs fitting
- CLs delivery/teach
- CLs aftercare
- Back to step 3 until we find CLs that work for the patient
What proportion of spectacle wearers are contact wearers in Australia? Which country has the highest proportion of contact wearers and what is the proportion?
5%.
Hong Kong has the most with 20% of the population wearing contacts.
What is the drop out rate for contact lens usage?
25-35%
What is the most popular contact material, contact design, and contact modality?
Silicon-hydrogel.
Spherical.
Daily.
In Australia, what are the trends of:
SCL material: more ... over time and less ...
SCL modality: more ... CLs over time and less ...
In Australia, what are the trends of:
SCL material: more SiHy over time and less hydrogel
SCL modality: more daily CLs over time and less monthly
How did Leonardo da Vinci contribute to contact lenses?
He employed two methods of immersing an eye in water with the idea of neutralising the cornea (with water) and replacing the cornea with a new refraction surface (bowl).
How did Adolf Fick contribute to contact lenses?
Described the first ..., which had ... and were filled with .... They were tolerated for approximately ... hours on .... Lenses were ..., suggesting that ....
How did Adolf Fick contribute to contact lenses?
Described the first glass contact lens, which had different diameters and were filled with 2% glucose solution. They were tolerated for approximately 8 hours on rabbit corneas. Lenses were unpowered, suggesting that altering front and back surfaces could correct ametropia.
What were the issues with Fick’s contacts? (4 points)
- only usable in primary position
- hard to manufacture
- expensive
- caused mechanical irritation
What did Josef Dallos note about contacts?
Poorly fitted contacts that had movement were best tolerated. He also noted that tears played a dual role in optics and metabolics.
How do contact lenses potentially impact corneal health? (5 points)
- mechanical reasons
- impedance of oxygen transmission
- introduction of foreign bodies/bacteria
- alterations to tear film structure/integrity
- corneal desensitisation
Describe the structure and physiology of the cornea.
Epithelium (most ... structure)
* ... of salts from stroma
* ... between cells
Endothelium (most ... structure)
* it’s a ... membrane
* has ... which actively ... into the aqueous
Describe the structure and physiology of the cornea.
Epithelium (most external structure)
* active transport of salts from stroma
* tight junctions between cells
Endothelium (most internal structure)
* it’s a semi-permeable membrane
* has carbonic-anhydrase Na+/K+ATPase pump which actively pumps Na+ into the aqueous
What determines corneal transparency? (2 points)
Corneal dehydration.
The pumps help maintain corneal deturgescence.
Describe the cornea’s metabolism.
Three main pathways:
* ..., ...%, ...
* ..., ...%, ...
* ..., ...%, ...
Describe the cornea’s metabolism.
Three main pathways:
* anaerobic glycolysis, 50%, anaerobic
* Krebs cycle, 15%, aerobic
* pentose phosphate, 35%, aerobic
Why is oxygen important for the cornea’s metabolism?
Oxygen is important because it is .... It is need to maintain the ... as well as ... and ....
... pumps transport ... into tear film and ... pumps transport ... into aqueous, so ....
Why is oxygen important for the cornea’s metabolism?
Oxygen is important because it is required for aerobic pathways. It is need to maintain the epithelial and endothelial pumps as well as corneal dehydration and transparency.
Epithelial pumps transport chloride into tear film and endothelial pumps transport bicarbonate ions into aqueous, so water follows in both cases due to osmosis.
What happens with corneal hypoxia? (11 points)
- reduced aerobic glycolysis
- accumulation of lactate in stroma
- osmotic imbalance
- corneal swelling
- loss of corneal clarity
- decrease in epithelial mitosis
- reduced number of corneal hemidesmosomes
- reduction is density of corneal nerve fibre endings
- epithelial microcysts and vacuoles
- endothelial abnormalities
- corneal neovascularisation
