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OPTICS

af Salma Yahaira Moreno Martinez

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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