Difference between Contact lens & Spectacles.pptx

This PPT is about Contact lens Vs Spectacles for correction of High Refractive Errors

1. Presented by:-Ranjita Amanatya Contact lens Vs Spectacles in High Refractive Errors

2. History of contact lenses

3. Spectacles Contact lenses Definition The optical appliance comprising lenses & frame, with sides extending towards the ears. An artificial device whose front surface substitutes anterior surface of the cornea. Types of Lens Materials 1)Organic materials (plastic):- a)Thermosetting ( eg :-CR-39, Zeiss duralet )
b) Thermoplastic ( Igard , Polycarbonate) 2)Mineral materials (glass):- 1) Focons ( eg :-PMMA,RGP lenses) 2) Filcons ( eg :-Silicone rubber elastomer) An ideal lens material High degree of transparency
Good impact resistance
Free from defects like bubbles
High index of refraction & low dispersion
Durable
Low weight
Easy to manufacture
Good scratch resistance
Inexpensive Biocompatibility
Optical properties
Gas permeability
Tolerance
Moulding
Sterility
Stability
Surface chemistry

4. Spectacles CL Vergence Vergence of eye not altered but vergence of rays is altered. Vergence of eye is altered causing change in Refractive power of eye. Position Placed 13mm in front of vertex plane Placed at the vertex plane Nomenclature 1)lenses 2)frame Abbe value:- Number which measures the degree to which light is dispersed (spread into different wavelengths) when entering a lens material off its centre. Reflectance Absorption Refractive index Specific gravity Base curve 1)Diameter a)Overall b) Optic zone 2)Curves Base Peripheral Central anterior Peripheral anterior Intermediate anterior 3)Blend 4)Edge 5)Power 6)Central thickness 7)Tint

5. Spectacles The surface that serves as the basis or starting point from where the remaining curves will be calculated. Affect distortion & magnification. LENS FORM Flat lenses Curved lenses Single cut meniscus lenses Lenticular lenses BASE CURVE

6. Spectacles Solid lenticular peripheral carrier convex Cemented Fused Myodisc Aspheric lenses HIGH PLUS POWER LENSES HIGH MINUS POWER LENSES

7. Contact Lenses Total power of CL:-Back curvature + Base curve + Actual power of CL Due to magnification caused by CL in comparison to spectacle lens Power of a (+) CL is always greater than spectacle power Power of a (-) CL is always less than spectacle power WETTABILITY

8. Contact Lenses BASE CURVE Back curve of the CL,which contours & aligns with the front surface of the cornea. Smaller the number in mm,more steeper is the base curve. Higher the diopter,steeper the base curve. TRIAL LENS BASE CURVE:- Measure horizontal & vertical meridian curvature in mm Take avg of two Add 1 to it SELECTION OF DIAMETER :- Add 2mm to the HVID to get the diameter of CL

9. VERTEX DISTANCE Distometer For convex For concave Away from eye:- Perceived power increases Away from eye:- Perceived power decreases CL fitted on the cornea:-No/Zero vertex distance Since refraction performed at 12-14mm,all CL above +/-4D need to be compensated for vertex distance CL power if glasses power is negative Glasses lens power whether negative or positive CL power if glasses power is positive -4.00 4.00 +4.25 -4.00 4.25 +4.50 -4.25 4.50 +4.75 -4.50 4.75 +5.00 -4.75 5.25 +5.25 -5.12 5.50 +5.87 -5.37 5.75 +6.12 Spectacles Contact Lenses

10. HIGH MYOPIA Full correction can rarely be tolerated in high myopia (more than -10D) An undercorrection to the tune of 1-3D or even more required depending upon age of the pt. & degree of myopia. Undercorrection done to avoid problem of near vision & minification of images. Avoid peripheral distortion & minification. Spectacles Contact Lenses

11. HYPERMETROPIA Most comfortable,safe & easy method of correcting hypermetropia. Indicated in U/L hypermetropia(anisometropia) Advantages over Spectacles:- Cosmetically better Increased field of vision Less magnification Elimination of aberrations & prismatic effect Spectacles Contact Lenses

12. APHAKIA About +10D with cylindrical lenses for surgically induced astigmatism are required. An addition of +3 to +4D required for near vision to compensate for loss of accommodation. Disadvantages:- Image magnification Spherical aberration Prismatic aberration Restricted field of vision Coloured vision Cosmetic blemish Cumbersome to use Problem of near vision Less magnification of image Elimination of aberrations & prismatic effect of thick glasses Wider & better field of vision Cosmetically more acceptable Better suited for uniocularaphakia More cost Cumbersome to wear,especially in old age & in childhood Corneal complications may be associated Spectacles Contact Lenses

13. BIFOCALS Executive Round Flat-top Two types:- Rigid gas permeable Soft CL Contact Lenses Spectacles

14. HIGH ASTIGMATISM REGULAR ASTIGMATISM IRREGULAR ASTIGMATISM Hard CL correct upto 2-3D of regular astigmatism. For higher degree of astigmatism, toric CL are needed. Bi-oblique astigmatism, mixed astigmatism & high astigmatism are better treated by CL than spectacles. Soft CL flexes to match the shape of the cornea & creates a uniform thickness tear film. Correct cylindrical error fully. REGULAR ASTIGMATISM CL replaces anterior surface of cornea in irregular astigmatism. Benefitted by RGP lenses. Contact Lenses Spectacles

15. ANISOMETROPIA The corrective spectacles can be tolerated upto a maximum difference of 4D, after that there occurs diplopia. In Anisometropic spectacles, margin of the stronger lens made weaker,thus minimizingannoyance caused by peripheral prismatic effect of conventional lenses. CL are useful in young children with high anisometropia. Spectacles Contact Lenses

16. Types High-Index Plastic Lenses Polycarbonate Lenses Trivex Lenses Aspheric Lenses Rigid Gas Permeable (RGP) Lenses Soft Contact Lenses Hybrid Contact Lenses Spectacles Contact Lenses

17. Improved Optical Quality Increased Comfort Cosmetic Appeal Thinner lenses Wider Field of Vision C:D Ratio:- Macula:- B.V.:- Periphery:- Easy to Use Low Maintenance Cost-Effective Wide Range of Frames Spectacles BENIFITS Contact Lenses

18. 1 2 3 c b a DISADVANTAGES Spectacles Contact Lenses Weight and discomfort Limited peripheral vision Cosmetic concerns Maintenance and hygiene Risk of complications Higher cost

19. 02 01 05 04 03 Complications of Soft Contact Lenses Corneal neovascularization Corneal epitheliopathy with FL staining Corneal edema with resultant myopic shift Toxic staining of cornea Superficial epithelial arcuate lesion(SEAL)

20. Spectacle blur Ghost images/flare Dessication of cornea Sattler’s veil Creeping myopia Distortion of shape of cornea 1 4 2 3 5 6 Common complications of Hard Contact Lenses