Types of RGP lens
- corneal
- corneal/scleral
- mini scleral
- scleral
Advantages of corneal RGP fitting
- robust
- easy to clean
- easy to handle
- stable vision
- good oxygen supply
- dehydration lens problematic
- customised design
- good tear exchange
Corneal RGP disadvantages
- physical comfort
- greater movement
- fb entrapment
When to choose an RGP
- moderate corneal astigmatism
- complex rx
- history of allergies
- problem with SCL
- financial
- poor compliance
- high visual demands
When to avoid an RGP
- contact sports
- water sports
- dusty environments
RGP parameters
- BOZR 1/1.5mm smaller TD
- FOZD 0.5mm larger than BOZR
- centre thickness - too thin causes flexage
- edge lift prevents mechanical pressure on cornea
RGP tear lens
- power increases by +0.25DS for each 0.05mm that BOZR is steeper
- BVP needs to be changed by -0.25DS for each 0.05mm to compensate
- opposite is also true
Spherical vs aspherical
Spherical - spherical back optic zone with spherical peripheral zones
Aspheric - elliptical lens design gradual flattening from centre out
Steps in selecting a first lens
- Find corneal shape/size/pupil/rx/health
- Choose separate lens type
- Work out shape you want
- Once shape selected, work out power using BVP calculation
Steps in Selecting RGP material
- Oxygen requirement - Dk - thin lens - increased O2 - thick lens - less O2
- Centre thickness
- Wettability
- Flexture can cause residual astigmatism
- Compliance, if poor go for easy care materials
Common RGP materials
- silicone acrylate
- flourosilicone acrylate - better wettability
- flourosilioxanyl sterene
BOZR considerations and calculation
-Difference in k readings is less than or equal to 1.00DC, then it to flattest k
- BOZR = flat k - (flat k - steep k) / 3
- round to nearest 0.05mm
What is an alignment fit
- good centration/constant pupil coverage
- no limbal crossing
- adequate movement on blink
- central trace of flouroscein
- midperipheral adequate band of bright flouroscein
- peripheral adequate band of bright flouroscein
What is a steep fit
- good centration
- no limbal crossing
- minimal movement on blink
- central bright area
- midperipheral wider band of touch
- peripheral adequate band of bright flourascein
Lid attached fit
Upper edge of lens tucked under top lid during blink
- common in large TD
- can actually be mo comfortable and less lid interaction
- acceptable as long as pupil is covered
Correcting a flat fit
- Steepen BOZR
- increase TD to stabilise lens
- use thinner lens to reduce eye movement
- BOZD increased by 0.05mm, BOZR requires to be flattened by 0.05mm
Correcting a steep fit
- flatten BOZR
- decrease BOZD
- thicker lens
- reduce TD to increase mobility
Over refraction
- tells us about the fit
- if good fit, over refraction 0 as BVP is based on refraction
- more plus/less minus - flat
- more minus/less plus - steep
-
Modality Of Wear13
-
SCL Fitting13
-
CLs And Oxygen10
-
CL Manufacturing22
-
SCL Complications29
-
SCL Care11
-
CL Aftercare7
-
RGP Fitting18
-
RGP I&R And Recording8
-
CL Compliance10
-
RGP CL Care4
-
SCL For Astigmatism10
-
RGP For Astigmatism9
-
RGP Complications15
-
Dry Eye In CLs8
-
CL Fitting For Presbyopia10
-
Corneoscleral GP Lenses5
-
CL Verification10
