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