Central topic

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OPTICS

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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

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