Intro to CLs Flashcards
Previous GP indication for soft CLs
Previous GP adherence & 3 and 9 oclock staining
CI for soft CLs
- Inflammation/ disease of AS
- Poor hygiene
- Chronic allergies/antihistamine used
- Systemic/Autoimmune/ immuno compromised diseases
- poor tear film
- irregular astigmatism
- Radial keratomy
- Dry/dusty enviroments
- giant papillary conjuctivitis
Rigid lenses include 2 types
PMMA and GP
Why are PMMA hardly used?
Rigid lenses with NO OXYGEN TRANSFER
What are GP made of?
How is the oxygen transfer?
Where do they sit in respect to the cornea?
Made of acrylic, silicone, flourine
Allows oxygen transfer but less than soft CLs
Sits ON the cornea
Soft CLS are made of ____.
How is their oxygen transfer?
Where do they sit in respect to the cornea?
Made of plastic polymer and water
Water allows the passage of Oxygen
Larger than cornea sits past the limbus
“Ideal CL fit”
Rigid lenses:
Soft CLs:
The lens to parallel the corneal shape for rigid
The lens to drape evenly for soft CLS
Lens will shift in a part of the cornea is too
Flat
What is a BC?
How steep or flat the center portion of the lens is
Usually same a corneal center
Soft lens fitting measurements
Focused on BC
Rigid lens fitting measurements
Focused on BC, secondary & tertiary curve
In order for a rigid lens to parallel the corneal shape, it must flatten in periphery as well
What are secondary and tertiary curves
Gradually flatten towards the edge
Numbers get larger BC-> SC->TC
How does a GP lens look and why?
Starts a bit steep toward the center and flatten as you go out to allow room for tears to move underneath the lens
The edge lift in a rigid lens allows tear exchange. This is important because it allows:
- Lens to move a bit
- Nutrients to get to the cornea
- Not having the tear film present would erode corneal
- Problems if too steep or edge is curved in
Multiple reasons why rigid lenses need the edge lift:
Tear exchange
Enhaced capillary attraction
Prevent erosion of cornea or epithelium
For the edge lift in rigid lenses the PC should be
A little flatter than the radius of curvature of the cornea in that area
Equation for effective power?
F2= F1/(1-dF1)
d= 12mm
Clinically, you should vertex any power that’s ___
4.00D and above. Anythig less, the change would be less tham 0.25 so insignificant
Minus lens are ___ effective when moved closer to the eye.
Will need ___ power in CL than specs
More effective
Less power in CL
Plus lens are ___ effective when moved closer to the eye.
Will need ___ power in CL than specs
Less effective
More power
How does vertex distance effect accommodation stimulus?
Myopes vs hyperopes
Myopes acc. Increased as lens is move towards the eye
Hyperopes acc decreases as lens is move towards the eye
Presbyopes response after CLs?
Myopes vs hyperopes
Myopes would notive NVA are affected in CL before glasses (woll need bifocals sooner bc of acc. Stimulus )
Hyperopes may be able to push it off for a bit longer in CLs than in glasses
_____ children with ___ AC/A ration should be encouraged to consider CLs.
Hyperopic with high AC/A ratios
Ortho at far and eso at near
Retinal image size is dependent on
Lens power and distance from the eye
