1. BY, PANARA SWATI FROM : BHARTIMAIYA COLLEGE OF OPTOMETRY 2ndYEAR 3rd SEMESTER 1 BEST FORM LENSES

2. HISTORY (1)HUYGENS(1629-95) Dutch physicist gave the wave theory of light. First suggested lenses should be corrected in some manner and proposed ratio of surface curvature 6:1. 2 3. (2)WOLLASTON(1804) An English physician first prepared periscopic lenses. Best forms were first went out by out Walt(1898) the French oculist. Later and in more detail by Percival of new castle(1901). 3 4. WHAT IS LENS? A lens is transparent refracting medium , bounded by two surfaces that form part of a sphere or a cylinder. 4 5. What is best form lenses? Ideal lens mean ,lens which correct all aberration but this is usually not possible. 5 6. AN IDEAL BEST FORM LENSES ISI Standard Good Material Standardize (ANSI-American National Standard Institue ,Z 87,Z87-2) Easy to manufacture and Process. Aberration free Inexpensive 6 7. TYPES (1)ASPHERIC LENSES (2)DEEP MENISCUS LENSES (3)LENTICULAR LENSES (4)PERISCOPIC LENSES 7 8. TYPES 8 Aspheric lens Deep meniscus lens Lenticular lens Periscopic lens 9. ASPHERIC LENSES A non spheric lens is called aspheric lens. These are used to make high plus aphakics lenses by modifying the lens curvature peripherally to reduce aberration and provide better peripheral vision. E.X. our cornea is also aspheric in nature. Aspheric lenses is depend upon the shape of the lens. 9 10. 10 11. 11 12. 12 13. 13 14. LENTICULAR LENSES A Lenticular lens is one in which the aperture containing prescribed power is smaller than the frame aperture in which it is glazed. The aperture is usually 30-40mm in diameter. These lenses have been created particularly to use in high power. It is also called high powered lens. 14 15. Thickness of the peripheral part poses a difficulty while fixing the lens to the frame. This difficulty is offset by grinding the peripheral part which reduce the thickness by 1.2-2.0mm and improves the cosmetic appearance as well. Lenticular lens is depend upon the shape of the lens. In Lenticular lens centre has power and periphery has no power. 15 16. 16 17. PERISCOPIC LENSES Lens with base of 1.25D is called a periscopic lenses. This lens is depended upon the base curve. Periscopic lenses are not much used nowdays. 17 18. DEEP MENISCUS LENSES A with a base curve of 6.00 D is called a deep meniscus lens. This lens is depended upon the base curve. 18 19. 19 20. In best form lenses the lens shape is also required to minimize the aberration also reduce effect of spherical and other aberration. For positive lens a negative base curve is used and for negative lens a positive base curve is used. So that if one error is allowed for other is automatically almost corrected. 20 21. 21