Rgp lens

Rgp lens

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 Soft contact lens 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…

4. 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.

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

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

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

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

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

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

11. 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

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

13. 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.

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

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

16. Edge configuration affects: Comfort Durability Tear meniscus

17. 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

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

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

20. Front surface design affects: Vision Lid interaction comfort movement centration

21. LENTICULATION Lenticulation defines the FOZR of a lens. Affects: Centre thickness Lens mass O 2 transmission Comfort

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

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

24. LENS DIAMETER and COMFORT

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

26. THANK YOU