CLs And Oxygen Flashcards by Nathan Ross

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Q

How does cornea receive oxygen

A

atmosphere
aqueous
perilimbal vasculature

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Q

What happens if the cornea doesn’t get enough oxygen

A

corneal oedema
neovascularisation
red and bloodshot
damage to endothelial layer
vulnerable to infection

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Q

What is oxygen transmissibility - Dk/t

A

the degree that oxygen passes through material of a given thickness

T=Dk/t

T= transmissibility
D= diffusion coefficient
k= solubility of oxygen in material
t= thickness

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Q

Corneal neovascularisation mechanism,signs and management

A

Caused by stromal oedema releasing vasostimulatory elements

no real symptoms
new BVs from limbus
manage by increasing Dk/t
good prognosis

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Q

What is polymegathism, signs and management

A

caused by long term hypoxia causing structural damage to endothelial cells

Signs
- no symptoms
- possible CL intolerance with reduced VA and Photophobia
- differing cell size in endothelium

Management
- refit with higher O2 lens
- change to dailies
- prognosis not good as endothelium doesn’t regenerate

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Q

What is myopic creep

A

optically stimulated myopic increase
counter balanced by higher modulus SiHy lenses, which flatten central cornea

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Q

Corneal oedema - SEAL, signs and management

A

superior epithelial arcuate lesions
caused by mechanical trauma by inflatable lenses
FB sensation
arcuate staining 1mm from superior limbus
manage by removing lens until clear
if persistent try flatter lens or RGP

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Q

Corneal oedema - striae

A

diabetics, elderly and keratuconus
caused by hypoxia - lactic acid causing osmotic shift
asymptomatic
manage by switching to dailies

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Q

Corneal oedema - endothelial folds

A

prevalent in older hydrogel EW lenses
caused by hypoxia and corneal oedema
Px may have blurred vision
straight dark lines in endothelial mosaic
switch to dailies and increase Dk/t

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Q

Benefits of SiHy, and what Px could be offered them

A

breathable for healthy wear
outstanding comfort
signs of corneal oxygen deficiency
possibly stopped wearing lenses due to discomfort
want to wear lenses full time

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