GLASS LENS MANUFAC

1. Ophthalmic Lens Manufacturing
PRESENTED BY-
MAAZ UL HAQ
C.L GUPTA EYE INSTITUTE
MORADABAD

2. Ophthalmic Lens Manufacturing
• Glass lenses

3. Glass lenses
• Early optical glasses were known as either crown or flint gl
ass
• The terms originated in interesting way
• The adjective crown was originally applied to window glass
used seventeenth and eighteenth century for houses in En
gland
• This glass was blown and whirled into a disk a knot left in t
he center by the working rod

4. • Before the development of optical glass the pieces of this g
lass is used for ophthalmic lenses and the lenses were kno
wn as crown lenses
• Today Crown glass refers to glass whose primary ingredient
s are silica, soda or potash and lime

5. • 1676, George Ravenscorft, an Englishman, used ground flin
ts as a source of silica and incorporated a relatively large q
uantity of lead as one of the basic constituents of glass
• The glass became known as Flint glass
• It was softer, heavier, clearer and more brilliant than any ot
her glass available and was used for drinking vessels, bowls
and quality crystal wear
• Today flint glasses are those contain lead oxide

6. Beginning of in 1876 Ernst Abbe and Otto Schott of Je
na, Germany collaborated in experimenting with larg
e number of chemical oxides in the manufacture of gl
ass and developed a wide range of new glasses
In 1880, the invention of barium crown by Abbe intro
duced a glass of high index without an appreciable inc
rease in dispersive power
Today Corning Inc. Pittsburgh Plate Glass Company an
d Scott glass Technologies, Inc. comprise the major gl
ass manufacture

7. Manufacturing of optical glass
• The ingredients are put into a melting pot 36 inches in diamet
er and 32 inches high, sufficient to make about 1000 pounds of
glass
• Ingredients depend on the type of glass to be made
• Are principally oxides or salts of metals including silica, sodium
and potassium, calcium and aluminum

8. • An additional ingredient, called cullet is waste glass from previ
ous metals
• Is added to save valuable raw materials and to form a glaze on
the surface of the pot, which reduces the corrosive action of t
he pot by melting of raw materials
• The pot is gradually raised to a temperature of 800 to 1000 an
d kept there for 3 to 5 days

9. • The pot is glazed by the use of small pieces of cullet.
• The ingredients are then added at intervals until the the temp
erature of the pot is raised about 1400
• The melting process the batch is full of bubbles of escaping gas

10. • This escaping of the gas is known as fining
• At the end of melting and fining process scum, stones and oth
er materials rise to the top of batch and are skimmed off
• The melt is then stirred constantly with long clay rods, which
may be moved either mechanically or by hand

11. • After melting, fining and stirring processes are completed, the
molten glass has the consistency of heavy syrup
• When cooled at a temperature of 1200, it is poured and rolle
d into sheets of various thickness and each sheet of glass is pla
ced in heated annealing oven in where it is gradually cooled to
room temperature

12. • After annealing the glass cut into small pieces is reheated and i
s then either pressed or molded into rough blanks
• After inspection the rough blanks are blocked or grinding shells
and the first surface ground and polished to the desired curvat
ure
• The blanks are then reblocked and ground and polished on the
second side

13. • This process called the batch process
• Was formally used for the manufacture of all optical glass
• Now it is used only for the production of relatively small quanti
ties of glass and many verities of coloured glass

14. • An automated method known as the continuous flow method
• Used for making large quantities of particular type of glass
• The process differs from the batch process in that molten glas
s is not poured into sheets but it is extruded, by means of conti
nuous process and pressed into molds to make the rough blan
ks

15. Desirable characterictics
• Homogeneity in both chemical composition and physical state
• Correct index of refraction and chromatic depression values
• Freedom from colour
• A high degree of transparency
• A high degree of chemical and physical stability

16. Ophthalmic crown glass
Silica (sand) 70%
Sodium oxide (soda) 14-16%
Calcium oxide (lime) 11-13%
And small percentage of potassium, borax, antimony
and arsenic
Used to manufacture single vision lenses and distanc
e portion of glass bifocal and trifocal lenses
Index of refraction is 1.523
And Abbe value is 59

17. ADVANTAGES
• Highly scratch resistant
• Resistant to solvents & temperature fluctuation
• Tinted by vaccum coating
• Good optical qualities
• High range curves blanks & addition available
• Available in photochromic sunglass option

18. DISADVANTAGES
• Low impact resistance
• Heavier material
• Chips can easily form while edging & handling
• Not apropriate for children & sport wear
• U.V. absorption not 100 % (upto 280nm)

19. Flint glass
Lead oxide 45% to 65%
Silica 25% to 45%
Mixture of soda and potassium oxide
Index of refraction 1.580 for light flint to 1.690 for de
nse flint
An Abbe value of 30 to 40
Used for bifocal segments for fused bifocals and sing
le vision lenses of high power because the high index
of refraction makes the lenses thinner

20. Barium crown glass
• Barium oxide 25% to 45%
• Barium oxide which has the same effect as lead oxide in increa
sing refractive index but without great increase in chromatic di
spersion
• Indices of refraction 1.514 to 1.616
• And Abbe values of from 55 to 59

21. HI-INDEX MATERIAL
• HI-index lenses have higher than standard refractive index
• Glass hi-index
Available in 1.6 , 1.7 , 1.8 , & 1.9

22. ADVANTAGES
• Available in range of lens types including photochromic , multif
ocal etc.
• Thinner than conventional lens materials
• Can be multicoated , tinted ,UV etc
• Available in wide range of blank size & finished as well as semi
finished lens types

23. DISADVANTAGES
• Greater distortions away from optical centre
• Not available in larger blank sizes
• Less impact resistant
• More chromatic dispersion
• Off axis abberation are seen
• Fragile