RGP Lenses

Question 1

PMMA Lens

Answer 1

• Durability and visual performance
• Resistant to scratches and to breakage
• Lens last long
• Surface can be polished
• Lens can be modified
• Best performance on corneas under 3.00D corneal cyl
• No permeability
• Can cause acute and chronic corneal hypoxia

Question 2

Gas Permeable Lens

Answer 2

• Oxygen transmitted through blinking and the material
• Can be made larger than PMMA providing more stability and better centration
• Easy to handle ( aphakic px or high plus) ex lens removal easier
• Can clean and polish easily
• Cost effective (longer life span)
• Can give clearer results than a soft on lower rx with astigmatism
  - 1.00 1.00 X090
• Cornea with high cyl can be fit successfully

Question 3

Advantage gas permeable lenses

Answer 3

• Rigid lens drops outs (PMMA) can be refitted immediately without having to wait for cornea to go back to normal shape.
• Keratoconus
• Reduces excessive spectacle blur
• Reduces Flare (PMMA had small OZ)
• Soft lens px drop outs
• GPC reduced from soft to gp

Question 4

Edge Clearance

Answer 4

• A small, peripheral gap between the edge of a rigid contact lens and the cornea
• Lens periphery is flatter than cornea
• Provides tear exchange for corneal metabolism
• Tear meniscus
• Assists in lens removal by the lids
• Avoids lens adhesion

Question 5

Little edge Clearance

Answer 5

• Inadequate tears exchange
• lens movement
• Arcuate staining
• Lens removal issues and adhesion

Question 6

Too much edge Clearance:

Answer 6

• Excessive lens movement
• Bubbles under the lens periphery which can cause frothing or dimpling
• Poor centration
• Lens displacement
• 3 and 9 o’clock staining