RGP fitting

Podcast Beta

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the primary advantage of using HDS - Hyperpurified Delivery System in fluorosiloxane acrylates?

Increased surface charge for better lipid attraction

Improved surface wettability due to the addition of fluorine monomers

Enhanced scratch resistance and lens flexure

Higher permeability due to the removal of inefficient Si molecules (correct)

What is the primary purpose of the GP design?

To ensure proper air bubble formation

To maximize the surface wettability of the lens

To match the back surface to the cornea and prevent decentration (correct)

To minimize lid irritation and assist centration

What is the characteristic of a fitting steep lens?

Central pooling, minimal movement on blink, and good centration (correct)

Peripheral curve aligns to the cornea, ensuring good fit

Liquid lens of 0.05mm equals 0.25D

Central touch, excessive movement on blink, and eye rotation

What is the minimum amount of astigmatism required for a toric GP lens?

2.00D Signup and view all the answers

What is the purpose of the toroidal zone in a toric GP lens?

To improve the physical fit and visual performance Signup and view all the answers

What is the primary advantage of using a back surface toric lens?

Better correction of astigmatism due to the difference in K Signup and view all the answers

What is the purpose of the liquid lens in a toric GP lens?

To smooth out low levels of astigmatism Signup and view all the answers

What is the result of using a spherical lens on a toric cornea?

Excessive lens awareness and poor vision due to flexure and centration Signup and view all the answers

What is the primary concern when fitting a patient with high astigmatism using RGP toric lenses?

Lens flexure due to the thinner lens design Signup and view all the answers

What is the recommended adjustment when the difference in K readings is less than 1DC?

Fit the lens 0.05mm steeper Signup and view all the answers

What type of RGP material is more prone to lens flexure?

Silicone acrylate Signup and view all the answers

What is the primary advantage of back-surface toric (BST) lenses?

Better physical compatibility with the cornea Signup and view all the answers

What is the purpose of the peripheral toric curve(s) in RGP toric lenses?

To allow even bearing and clearance at the periphery Signup and view all the answers

What is the recommended approach when adjusting the spectacle Rx for CL rotation?

Adjust the spectacle Rx using the LARS method Signup and view all the answers

What is the effect of a steep lens on the tear lens?

It results in a positive tear lens Signup and view all the answers

What is the primary disadvantage of RGP toric lenses?

Relatively thick CLs Signup and view all the answers

What is the recommended trial lens diameter for patients with wide palpebral apertures?

Smaller TDs Signup and view all the answers

What is the optimal fitting characteristic of an RGP toric lens?

Static central fluorescein pattern Signup and view all the answers

What type of lens is used when there is ocular astigmatism with a spherical cornea?

Front Surface Toric lens Signup and view all the answers

What is the purpose of prism ballast in Translating Bifocal lenses?

To stabilise the lens Signup and view all the answers

What is the effect of a thicker lens in Translating Bifocal lenses?

Rides high on blink, reducing comfort and oedema Signup and view all the answers

Why is the BOZD 1-1.5mm smaller than the total diameter (TD)?

To cover the pupil in different light conditions Signup and view all the answers

What is the effect of a steep BOZR on the tear lens power?

It increases by about +0.25 D for each 0.05mm Signup and view all the answers

What is the purpose of selecting a RGP material with high DK?

To make the lens thinner and easier to handle Signup and view all the answers

What is the effect of a centre thickness that is too thin?

It leads to flexure and breakage Signup and view all the answers

Why is the lens fitted 0.1mm flatter than the flattest K?

To allow for close alignment and adequate edge clearance Signup and view all the answers

Which of the following RGP materials is known for its good wettability and fewer deposits?

Fluorosilicone acrylate Signup and view all the answers

What is the primary concern when fitting a patient with high astigmatism using RGP toric lenses?

Lens flexure Signup and view all the answers

What is the purpose of the peripheral toric curve(s) in RGP toric lenses?

To improve centration Signup and view all the answers

What is the recommended adjustment when the difference in K readings is less than 1DC?

Fit 0.05mm steeper than the flattest K Signup and view all the answers

What is the primary advantage of using a back-surface toric (BST) lens?

Physical compatibility with the cornea Signup and view all the answers

What is the effect of a steep lens on the tear lens?

More minus power is required Signup and view all the answers

What is the recommended approach when adjusting the spectacle Rx for CL rotation?

Adjust the spectacle Rx Signup and view all the answers

What is the primary disadvantage of RGP toric lenses?

Relatively thick lenses Signup and view all the answers

What is the recommended trial lens diameter for patients with wide palpebral apertures?

Smaller TDs Signup and view all the answers

What is the primary reason for using Fluorosiloxane Acrylates?

To reduce the surface charge of the lens Signup and view all the answers

What is the effect of a spherical lens on a toric cornea?

It causes both excessive lens awareness and poor vision Signup and view all the answers

What is the purpose of the AERCOR Technology?

To replace impermeable PMMA traditional polymer foundation Signup and view all the answers

What is the result of using a liquid lens with a TD +0.50mm?

A flatter BOZR with a 0.05mm reduction Signup and view all the answers

What is the primary advantage of using a toroidal periphery in a toric GP lens?

It provides better stability and comfort Signup and view all the answers

What is the recommended approach when ordering a back surface toric lens?

Order empirically using K9s and spec Rx Signup and view all the answers

What is the effect of a central steeping of the cornea on the peripheral curve?

It causes a flatter peripheral curve Signup and view all the answers

What is the primary concern when fitting a patient with high astigmatism using GP lenses?

Lens flexure and decentration Signup and view all the answers

What is the primary advantage of using a front surface toric lens?

Lens need to orientate correctly Signup and view all the answers

What is the result of using a lens with a centre thickness that is too thin?

Lens becomes more prone to flexure Signup and view all the answers

What is the effect of a steep BOZR on the tear lens power?

Tear lens power increases by about +0.25 D for each 0.05mm Signup and view all the answers

What is the primary purpose of the edge lift in RGP lens design?

All of the above Signup and view all the answers

What is the recommended approach when fitting a translating bifocal lens?

Add set 3mm from the geometric centre of the lens Signup and view all the answers

What is the primary advantage of using a high DK RGP material?

Thins the lens and allows more oxygen permeability Signup and view all the answers

What is the characteristic of a concentric bifocal lens?

Central optical zone is smaller than the pupil Signup and view all the answers

Why is the BOZD 1-1.5mm smaller than the total diameter (TD)?

To ensure the lens covers the pupil in different light conditions Signup and view all the answers

Study Notes

Flouro-Siloxaine Acrylates

Fluorine monomer added to SA, resulting in lower surface charge, better wetting, and less deposits, although it attracts lipids and mucus
Dk 40 - 100+, susceptible to scratching and lens flexure
HDS - Hyperpurified Delivery System removes inefficient Si molecules, resulting in higher permeability (40 Dk) and improved surface wettability with high % MMA

AERCOR Technology

Oxygen permeable backbone replaces impermeable PMMA traditional polymer foundation, allowing high DK/t and material strength
Permits reduction in silicone (Boston EO)
Surface treated with plasma, graft polymerization, and hydrolysable lens to improve wetting

GP Design

Designed to match back surface to fit cornea, preventing indentation and allowing tear circulation, not causing lid irritation and decentration
TD large enough to encompass BOZD and peripheral curves, with minimal lid irritation and assisting centration
Cornea is aspheric central steeping and flatter towards periphery, peripheral curve aligns to cornea, ensuring good fit

Fitting Steep vs. Flat

Fitting Steep: Central pooling, minimal movement on blink, good centration, and air bubble
Fitting Flat: Central touch, excessive movement of lens, blinking and eye rotation, uncomfortable

Liquid Lens

0.05mm = 0.25D, TD +0.50mm = flatter BOZR 0.05mm

Toric GP

Spherical lens on toric cornea can cause excessive lens awareness, rocking, poor vision due to flexure, and centration
>2.00D astigmatism can be corrected with toric GP, with toroidal periphery providing better stability and comfort
Tear film corrects some astigmatism; toroidal periphery gives better stability and comfort

Back Surface Toric

For difference in K in excess of 0.50mm, improved physical fit and visual performance
Order empirically using K9s, spec Rx, and BVD
Rx in minus cyl form (Sphere @flat, Sphere + Cyl @ steep)
Lens will align with principal meridian, no stabilization required

Bi-toric

Toroidal front and back surface, used when back surface toric leaves residual astigmatism (ocular not equal to corneal astigmatism)
Order and fit in the same way as back surface toric (add residual astigmatism to steeper meridian)
No stabilization is required

Front Surface Toric

Used when there is ocular astigmatism with a spherical cornea, lens needs to orientate correctly
Stabilization is required
BOZR and TD selected as spherical GP, specify astigmatism and axis, and request prism ballast
Reorder to account for any rotation if necessary

Translating Bifocal

Near vision in the lower half of CL, lenses translate upwards and outwards as eye looks down and convergence due to upper lid traction at the edge of lens
Design: Prism ballast stabilization, solid image jump with down gaze unless OC aligned
High refractive index so less jump
Back surface solid tears neutralize 2/3 power of add, front surface segment = glare and flare
D seg and Executive style bifocal

Toric GP Fitting

Successful but limited to GP wearers, niche
Fitting: typical PD on downgazes assumed to be 3.5-4mm, typical GP movement is 2mm on downgaze
Add set 3mm from geometric center of lens
Thicker lenses less likely to ride high on blink, reduced comfort and oedema
Lens must rise ½ of PD
If eyelid below limbus, translating not recommended
Generally fitted 0.1mm flatter than flattest K to allow close alignment and adequate edge clearance

Concentric Bifocal

Central optical zone smaller than pupil, either distance and near surround or vice versa
Reduced contrast and VA due to blurred image
Haloes, near impairment with pupil constriction with D centre, decentration causes blur
Pupil dependent

Care System

Boston 2 step (Cleaner and conditioner) or GP multi-action and flat case

RGP Material Selection

Corneal O2 requirements: DK, Thins lens more O2, thick lens easier to handle
Centre thickness: consider edge form, maximum wearing time
Wettability: ability of tears to form a stable layer on top of the CL
Flexure: can cause residual astigmatism on toric corneas, especially true on thinner lenses
Compliance: common RGP materials include silicone acrylate, fluorosilicone acrylate, and fluorosiloxanyl

RGP Toric Fitting

CL Types: Front-surface toric (FST), Back-surface toric (BST), Bitoric (Bitor), and Peripheral toric
Problems: poor vision, poor centration, CL rocking on the flat meridian, unstable CL fitting, CL flexure, harsh bearing areas, corneal distortion, spectacle blur, discomfort, poor blinking, and epithelial damage
Advantages: stabilized CL fitting, improved CL-cornea fitting relationship, cylindrical correction maybe less than with toric SCLs, and better corneal physiology than toric SCL