5.1.3 Chooses, fits and orders rigid lenses Flashcards
What are the reasons for fitting RGP?
- Aphakia
- Cornea with high DC
- Keratoconus
- Post-Graft Surgery
- Visually:
- Better vision with high rx
- More durable à up to 1 yr wear
Health: - High o2 permeability
- Doesn’t dry out tear film due to 0% water content
- Resistant to protein deposits
How do you fit an RGP?
- TD: Related to TD of the lens, HVID – 2mm
- BOZR: Radius of Curvature of the lens
o Related to K-readings, most are fittest to flattest K - BOZD: Diameter of the optic zone
o Related to max pupil size
Assessing Fit: - MOB 1-2mm is acceptable with no limbal excursion
Describe common RGP lens materials?
- Flouro-Siloxaine Acrylates – Fluorine monomer added to SA, lower surface charge so better wetting and less
deposits – although attracts lipids and mucus. Dk 40- 100+. Susceptible to scratching and lens flexure. - HDS – Hyperpurified Delivery System removes inefficient Si molecules so higher permeability, 40 Dk, High % MMA
gives improved surface wettability. - AERCOR Technology - Oxygen permeable backbone, replaces impermeable PMMA tradition polymer foundation,
allows high DK/t and material strength. Permits reduction in silicone (Boston EO). - Surface Treated - Plasma, Graft polymerisation and hydrolysable lens – improve wetting.
Describe the design of GP lenses?
o match back surface to fit cornea, prevent indentation of cornea and allow tear circulation, not to cause lid
irritation and prevent decentration. TD large enough to encompass BOZD and peripheral curves. Minimal lid
irritation and assist centration.
o Cornea is aspheric – central steeping and flatter towards periphery – peripheral curve aligns to cornea and
ensure good fit.
* Fitting – Steep – Central pooling, minimal movement on blink, good centration, 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
Describe No 7 Quasar lens?
