Downloaded 163 times
More Related Content
Lens material
- 1. LENS MATERIALS PRESENTED BY: SHOAIB AKHTAR
- 2. OBJECTIVE • Introduction toophthalmic lens and its material • Glass material –history and its types • Plastic material – history and its types • Properties of ophthalmic lenses- its classifications and sub classification
- 3. WHAT IS OPHTHALMICLENS ? • It is the portion of the transparent medium bounded by two refracting surfaces at least one of which is curved.
- 4. LENS MATERIAL • Ophthalmiclens materials means all materials used during manufacturing, i.e. all materials entered into the composition of the basic ophthalmic lens. • There are two types of lens material. (1) Glass (2) Plastic
- 5. GLASS MATERIAL • Glassmaterial often referred to as mineral lenses. Advantages 1. Absorb heat and cold 2. Are scratch resistant 3. Highest optical clarity 4. Low Aberration
- 6. HISTORY OF GLASSMATERIAL • Early optical glasses were known as either crown or flint glass. • The adjective crown was originally applied to window glass used seventeenth and eighteenth century for houses in England. • Before the development of optical glass the pieces of this glass is used for ophthalmic lenses and the lenses were known as crown lenses.
- 7. Cont... • Today Crownglass refers to glass whose primary ingredients are silica, soda or potash and lime. • 1676, George Ravenscorft, an Englishman, used ground flints as a source of silica and incorporated a relatively large quantity of lead as one of the basic constituents of glass. • The glass became known as Flint glass.
- 8. Cont... • It wassofter, heavier, clearer and more brilliant than any other glass available and was used for drinking vessels, bowls and quality crystal wear. • Beginning of in 1876 Ernst Abbe and Otto Schott of Jena, Germany collaborated in experimenting with large number of chemical oxides in the manufacture of glass and developed a wide range of new glasses.
- 9. Cont... • In 1880,the invention of barium crown by Abbe introduced a glass of high index without an appreciable increase in dispersive power. • Today Pittsburgh Plate Glass industries and Scott glass Technologies comprise the major glass manufacture.
- 10. CROWN FLINT GLASS GLASS BARIUMHIGH CROWN INDEX GLASS GLASS 10 TYPES OF GLASS MATERIAL
- 11. CROWN GLASS • 70% Silica , 14- 16 % sodium oxide , 11- 13 % calcium oxide and small percentage of potassium , borax , antimony , arsenic. • Used for single vision lenses • Most common used in ophthalmic industry
- 12. Cont... • Refractive index-1.523 • Abbe value - 59 • Specific gravity- 2.54 • Transparency- 91.6%
- 13. Cont... Advantages • Highlyscratch resistant • Good optical qualities • Available in single vision and multifocal lenses • Available in photochromic sunglass option • Low cost • Reduce chromatic aberration
- 14. Cont... Disadvantages • Lowimpact resistance • Heavier material • Chips can easily form while edging
- 15. FLINT GLASS • Leadoxide 45% to 65% • Silica 25% to 45% • Mixture of soda and potassium oxide • Used for bifocal segments for fused bifocals and single vision lenses of high power because the high index of refraction makes the lenses thinner.
- 16. Cont... • Refraction index-Light flint : 1.580 - Dense flint : 1.690 • Abbe value - 30 to 40 Advantages • Available in single vision and bifocal lenses Disadvantages • Transparency less than crown glass • Distortion of image
- 17. BARIUM CROWN GLASS •Barium oxide 25% to 45% • Barium oxide which has the same effect as lead oxide in increasing refractive index but without great increase in chromatic dispersion. • Refractive index - 1.514 to 1.616 • Abbe values - 55 to 59
- 18. HIGH INDEX GLASS •There are higher index glass lens materials available that will reduces thickness for higher powered lenses. • Contents- High % of Titanium oxide • Refractive index- Available in 1.6 , 1.7 , 1.8 , & 1.9 • Abbe value – 33 , 32 , 31 , 30
- 19.
- 20. Cont... Advantages • Availablein range of lens types including photochromic , multifocal etc. • Thinner than other lens materials • Can be multicoated • Available in wide range of blank size & finished as well as semi finished lens types
- 21. Cont... Disadvantages • Greaterdistortions • Not available in larger blank sizes • Less impact resistant • More chromatic dispersion • Off axis aberration are seen
- 22. PLASTIC LENS MATERIAL •It is a polymeric material of large molecular wt. which can be shaped by flow. • Also called as organic material. • Most plastics are synthetic materials formed by combining various organic ingredients with inorganic materials such as carbon, hydrogen, nitrogen, chlorine & Sulphur.
- 23. HISTORY OF PLASTICMATERIAL • Just as World war 1 served as the impetus for the development of optical glass industry, World war 2 served as the impetus for the development of the plastic industry. • Plastic material developed during the 2 World war were PMMA develop CR39 for use in military aircraft. • In 1947 Robert Graham formed Armorlite lens company in California later described the first ophthalmic lens made from CR39.
- 24. Cont... • In 1957General Electric developed a new plastic material a Polycarbonate called Lexan. • In 1982 Corning glass work the development of a lens called Corlon.
- 25. CR39 POLYCAR BONATE TRIVEX HIGH LENSESINDEX PLASTIC 25 TYPES OF PLASTIC MATERIAL
- 26.
- 27. CR39 • It isalso called as Columbia resin or allyl diglycol carbonate. • CR – 39 or allyl diglycol carbonate is a plastic polymer commonly used in manufacture of eye lenses. • It was developed by (PPG) Pittsburgh Plate Glass industries. • It is the thermosetting material.
- 28. Cont... • CR standsfor Columbia Resin & it is 39th formula of a thermosetting plastic developed by the Columbia resin project of (PPG) industries back in 1940. • “CR” stands for Columbia Resin, and the number 39th denotes the type of Columbia Resin used. • For years CR- 39 was used without anti scratch coating.
- 29. Cont... • Now, however,most CR-39 lenses come with an anti scratch coating, making the material much more scratch resistant. • CR-39 plastic lenses do not fog up as easily as glass lenses.
- 30. Cont... • Refractive index- 1.498 • Abbe value - 58 • Specific gravity - 1.32 Advantages • Lighter weight than glass lenses • Impact resistance • Resistance of fogging
- 31. Cont... Disadvantages • Can yellowwith age • Scratches more easily • Surface abrasion
- 32. POLYCARBONATE • Polycarbonate isa thermoplastic. • The lens material is soft and requires an anti- scratch coating. • It was developed in the 1970s for aerospace application, and is currently used for the helmet visors of astronauts and for space shuttle windshields.
- 33. Cont... • Eyeglass lensesmade from polycarbonate were introduced in the early 1980s in response to demand for lightweight impact resistance lenses. • Refractive index- 1.586 • Abbe value- 29 • Specific gravity- 1.20
- 34. Cont... Advantages • Lightestof all material • Most impact resistant material • 30-40% thinner than CR39 • Absorb 100% UV rays Disadvantages • High chromatic aberration • More scratches and more epensive • Transparency less
- 35. HIGH INDEX PLASTIC •Plastic are made up of Thermosetting plastics. • These lenses have higher than standard refractive index. • Most cosmetically acceptable lenses. • It enable the lens to bend light “faster” than other. • Hence they are lighter and thinner than standard lenses.
- 36. Cont... • Refractive index– 1.66 • Abbe value – 32 • Density – 1.35 Advantages • Cosmetically good • Magnification is reduced • Thinner and lighter than other lenses
- 37. Cont... • Available inrange of lens type including photochromatic , multifocal etc • Impact resistant Disadvantages • Greater distortion • Not available in larger blank size • More chromatic dispersion • Off axis aberration are seen • Expensive
- 38. TRIVEX LENSES • Trivexlenses developed by PPG industries. • The lens material was originally for military use. • The lens material to provide excellent safety for window in combat vehicles and good optics. • Similar to polycarbonate but have higher quality optics & thus provide clearer vision.
- 39. Cont... • Refractive index– 1.523 • Abbe value – 35 to 43 • Density – 1.11 Advantages • Impact resistance • Lighter in weight Disadvantages • More scrach
- 40.
- 41. OPTICAL PROPERTIES 41 ABBE VALUEREFLECTANCE REFRACTIVE INDEX ABSORPTION
- 42. ABBE VALUE • DEFINITION: Reciprocal of the dispersive power of the material and gives a measure of the material ability to transmit the light. • Abbe number of 60 is considered to have the least chromatic aberrations and Abbe number of 30 is for the most chromatic aberrations. • Most high index materials have a much lower Abbe value.
- 43. REFLECTANCE • Reflectance isthe phenomenon of light reflection occurs at each of the lens surfaces. • The result is the loss of lens transparency and undesirable reflections on the lens surfaces. • The reflectance of the lens surface is calculated from the refractive index of the material.
- 44. REFRACTIVE INDEX DEFINITION :The ratio of speed of light in a vacuum to the speed of light in a given medium. • The higher the R.I. the thinner the lens can be made. • Materials with an index between 1.523 and 1.57 are considered as mid-index, while 1.58 and greater is considered as high-index.
- 45. ABSORPTION • The amountof light which goes through a lens can be reduced because of absorption by the lens material. • This is negligible in case of a non–tinted lens, but constitutes an function of a tinted or photo chromatic lens.
- 46.
- 47. SPECIFIC GRAVITY DEFINITION :The ratio of the density of a substance to the density of some substance (such as pure water) taken as a standard when both densities are obtained by weighing of air. • Which tell us about the relative weight of the material with respect to same amount of water. • The higher the specific gravity of a lens material, the higher will be the density and heavier will be the lens.
- 48. IMPACT RESISTANCE DEFINITION :is the ability of a material withstand a high force or shock applied to it over a short period of time. • Relative impact resistance of various materials will vary, depending on the size and shape of the missile used in the test. • Polycarbonate is the most impact resistance material.
- 49.
- 50. SCRATCH RESISTANCE • Lensesthat are treated front and back surface with a clear, scratch resistance coating have a much harder surface that is more resistance to scratching. • Front and back surface features of glass lenses is scratch (abrasion) resistance. • Plastic lenses need to be coated with an additional resin to approach the scratch resistance of glasses.
- 51.
- 52. ELECTRICAL PROPERTIES • Electricalproperties characterize effects of electromagnetic waves and electricity on the materials.
- 53. CHEMICAL PROPERTIES • Chemicalproperties shows the reaction of materials to the chemical substances usually found during lens manufacture, andin every day life. • These substances are usually hot or cold water, acids and organic solvents.
- 54. THERMAL PROPERTIES • Thermalproperties changes of state and the effect of temperature on materials.
- 55. REFERENCE • System forophthalmic Dispensing Clifford W. Brooks and Irvin M. Borish • Internet
- 56.