Center Thickness, order as TAP
Thinner lens more flexible, will get distorted on keratoconic eye
Thicker lens heavier, more likely to drop
RGP Fitting Parameters
Tear Lens
Flat BC to K for lid held position
Steep BC to K relationship secures centered lens
Peripheral Curve Radius
Edge Pattern
Excessive Edge Lift
Solution: Steepen PC
Minimal Edge Lift
Solution: Flatten PC
3 CR= 2CR + 1.5 mm
2 CR= BCR + 1 mm
Total Diameter
Vertical Aperture Size
Diameter should be at least smaller than vertical aperture
HVID
HVID -2.5 mm
If too small, increase
If too large, decrease
BC Radius
Problem: Too Flat
Apical Touch
Decrease BC radius/ Steepen BC radius
Problem: Too Steep
Apical Clearance
increase BC radius/ Flatten BC radius
Material
Peripheral Curve Width
3CW= 1/2 (2CW)
Junctions
Blended to improve comfort
Heavy
Medium
Light
Optic Zone Diameter
TD = OZD + 2 (2CW) + 2 (3CW)
OZD = Pupil Size + 2mm
initial: 2 mm larger than pupil size measured in dim illumination
If peripheral blur or glare greater in dim, increase OZD
Fitting Philosophy
Aperture Position
Lens centered in front of pupil
When flat K is > 45.00 D
When corneal cyl is 2.00-2.50 D, diagnostic BC 1.0 mm steeper than flat K
When aperture is > 10.5 mm
Diagnostic (small) diameter 9.0 or < when Plano to -8.00
Lid Held Position
Superior lens edge remains under upper lid
Diagnostic BC is 0.1 mm flatter than flat K
Diagnostic lens diameter is 9.5-10 mm, OZD is 1-1.8 mm < diameter
When myopia is Plano to -8.00
When pt aperture is 9-10.5 mm
When flat k is <44.75
When cornea is spherical or up to 1.5 D WTR
Main topic
