wk2: CL/M - Nomenclature and Verification of CLs Flashcards
Why is CL verification necessary? (4)
To confirm lens received is as ordered
To identify parameters of lens prescribed elsewhere
Confirm parameters of trial lenses
Ensure that the lens meets ISO standard
Define BOZR
Back Optic Zone Radius
Define BOZD
Back Optic Zone Diameter
Define BPR
Back Peripheral Radius
Define BPZD
Back Peripheral Zone Diameter
Define TD
Total Diameter
Define FOZR
Front Optic Zone Radius
Define BVP
Back Vertex Power
Define CT
Centre Thickness
Define ET
Edge Thickness
Define Dk
Oxygen permeability
Define Dk/t
Oxygen transmissability
What tool is used to verify the BOZR/BC in RGPs?
Radiuscope (optical microspherometer)
What techniques can be used to verify the BOZR/BC in SCLs? (3)
Template method
Radiuscope
Spherometer (optimec device)
What is the “Drysdale’s principle”?
For a curved mirror, an image is formed in the same plane as the objectwhen the object is at the centre of curvature of the mirror
Briefly explain how a radiuscope (optical microspherometer) works (3)
The curved surface of the contact lens acts as a mirror. Two images of the projected target are formed: a surface image and cleaner aerial image. The distance between focusing these two images gives the radius of curvature of the contact lens
Describe the procedure to use a radiuscope to measure radius of curvature (6)
Centre the beam on the CL
Focus target image on lens surface (surface image)
Set internal scale to zero
Obtain aerial focus (aerial image) by moving microscope up
Read radius of curvature off the internal scale
Use an average of 3 readings
When using a radiuscope to measure radius of curvature, in what size steps should you work in?
work in 0.5mm steps
How accurate is the internal scale at measuring radius of curvature in radiuscopy?
within 0.01-0.02mm
How does radiuscopy differ for toric lenses? Explain
Toric lenses have two radii of curvature, meaning that not all spokes of the aerial image will come into focus together. This means that 2 radings willn eed to be taken