CLs & O2 Flashcards
How cornea receives O2
- atmosphere
- aqueous
- perilimbal vasculature
What happens if corneal doesn’t get enough O2
- corneal oedema
- neovas
- red + bloodshot
- damage to endothelial layer
- venerable to infection
What is O2 transmissibility Dk/t
degree that O2 passes through material of a given thickness
T=Dk/t
T = transmissibility
D = dissuasion coefficient
k = solubility
t = thickness
Corneal neovascularisation
Aetiology
- stromal oedema releasing vasostimulatory elements
symptoms
- none
Signs
- new BVs from limbus
Management
- increase Dk/t
- good prognosis
Polymegathism
Aetiology
- long term hypoxia causing structural damage to endothelial cells
Symptoms
- possible Cl intolerance
- reduced vision + photophobia
Signs
- reduced VA
- differing cell size in endothelium
Management
- refit with higher O2 lens
- change to dailies
- prognosis not good as endothelium doesn’t regenerate
Myopic creep
- optically stimulated myopic increase
- counter balanced by higher modulus SiHy lenses which flatten central cornea
Corneal oedema - SEAL
superior epithelial arcuate lesions
Aetiology
- mechanical trauma by inflatable lenses
Symptoms
- FB sensation
Signs
- arcuate staining 1mm from superior limbus
Management
- remove cl until clear
- if persistent try flatter lens/RGP
Corneal oedema - striae
Aetiology
- diabetics, elderly, keratuconus
- caused by hypoxia - lactic acid causing osmotic shift
Symptoms
-asymptomatic
Management
- switch to dailies
Corneal oedema - endothelial folds
Aetiology
- prevalent in older hydrogel & EW lenses
caused by hypoxia & corneal oedema
Symptoms
- may have blurred vision
Signs
- straight dark lines in endothelial mosaic
Management
- switch to dailies
- increase Dk/t
Benefits of SiHy + what px offered them
Benefits
- breathable for healthy wear
- outstanding comfort
Px category
- signs of corneal O2 deficiency
- possibly stopped wearing lenses due to discomfort
- want to wear lenses F/T
