Rigid gas permeable (RGP) contact lenses are rigid plastic lenses that transmit oxygen. They have inherent rigidity like PMMA but are semi-soft due to oxygen permeability. RGP lenses provide clearer vision than soft lenses, are more durable, and less expensive. However, they require an adaptation period and have a higher risk of dislodging than soft lenses. Key design features of RGP lenses include the back surface design, thickness, edge configuration, and diameter, which affect lens fit, movement, comfort, and vision. RGP lenses are used to correct astigmatism and presbyopia and for conditions like keratoconus.

1. RGP LENS
PRESENTED BY;
SNEHA XAVIER

2. CONTACT LENS
• Contact lens is a thin lens placed on the surface
of the eye to correct vision,for cosmetic or
therapeutic reasons instead of wearing glasses.
• It is of two types on the basis of material
i. Soft contact lens
ii. RGP or Hard CL
 Rigid gas permeable contact lenses are rigid
lenses made up of durable plastic that transmits
oxygen.

3. • Rigid Gas Permeable lenses are those lenses
made up of materials which are permeable to
oxygen.
• They have inherent rigidity similar to PMMA , but
due to their oxygen permeability they have
become popular by name semi soft lenses.
• Made up of polymers e.g. silicone resin ,
polystyrene…

5. Advantages of RGP lenses;
• Provide clearer vision than soft contact lenses.
• More durable
• Less expensive than soft contact lenses.
• It is used to perform orthokeratology , where
contact lenses are worn during sleep to reshape
the cornea and improve vision.

6. Disadvantages ;
• Need time for adaptation
• Increased possibility of dislodging
• Vulnerability to sand and dust

7. The desirable properties of RGP lenses;
1. Optimal design.
2. Material:
wettability
deposit resistance
stability
high Dk

8. DESIRED FITTING
 Moderate edge width and clearance
 central and mid-peripheral alignment
 Smooth movement
 centration

9. • Comfortable
• Clear vision
• Adequate wearing time
• Minimal ocular response
• Normal facial appearance
DESIRED PERFORMANCE

10. KEY DESIGN FEATURES
• Back surface design
• Back optic zone diameter
• Front surface design
• Lens thickness
• Edge configuration
• Lens diameter

12. BACK SURFACE DESIGN
• Controls Lens/Cornea Interaction
• This interaction largely controls the lens fit and
affects
centration of lens
movement of lens

13. BACK SURFACE DESIGN FREEDOM
Back surface design is somewhat limited by the
fact that it must be related to the corneal shape in
a acceptable way.
Possiblities for the final overall shapes are;
• Aspherical or Spherical shape
• Single or multiple curves

14. continuation....
fitting relationship broadly fall into falling
categories;
steeper than cornea
Aligned with the cornea
Flatter than cornea

15. BACK SURFACE DESIGN CLINICAL
CONSIDERATIONS
• Central fluorescein pattern: The use of fluorescein
is a sensitive technique for comparing corneal
shape to that of the CL.
• Corneal curvature changes.

16. BACK SURFACE DESIGN FLUORESCEIN
PATTERN
BOZD
Ideal
Aspheric
Spherical
BOZD

18. Excessive reservoir
loose fit
Inadequate reservoir
tight fit
WIDE
edge
NARROW
edge
EDGE WIDTH AND TEAR RESERVOIR

19. Edge configuration affects:
• Comfort
• Durability
• Tear meniscus

20. EDGE SHAPE vs COMFORT
• RGP lenses with rounded and square posterior
edge profiles are more comfortable
• Comfort is determined by interaction of lens edge
with the lid

22. LENS THICKNESS
Determined by:
• Rigidity of the material
• Permeability
• Back vertex power(BVP)

23. FRONT SURFACE DESIGN
Controlled by:
• BVP
Design Freedom:
• FOZD
• Front peripheral curves
• Their radii and widths

24. Front surface design affects:
• Vision
• Lid interaction
- comfort
- movement
- centration

25. LENTICULATION
Lenticulation defines the FOZR of a lens.
Affects:
• Centre thickness
• Lens mass
• O2 transmission
• Comfort

26. LENS DIAMETER
Determined by:
• Corneal diameter of population
• HVID of patient
• Inter- palpebral aperture
• Lens power (minus/plus)

28. Lens diameter affects:
• Centre of gravity
• Stability
• Option to have larger BOZD/FOZD
• Comfort
• 3 & 9 staining

30. LENS DIAMETER and COMFORT

31. APPLICATIONS OF RGP LENS
• Astigmatism correction.
• Children and teenagers.
• Presbyopia – bifocal correction.
• Irregular cornea – keratoconus
• orthokeratology