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Lec 3 OPTO 225 (Ophthalmic Optics and Dispensing I)

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Nada ALdahlawi

on 20 September 2018

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Transcript of Lec 3 OPTO 225 (Ophthalmic Optics and Dispensing I)

Lecturer: Dr.Nada Aldahlawi
Email: naldahlawi@ksu.edu.sa

Lec 3 OPTO 225 - Ophthalmic Optics and Dispensing I
Plastic materials
Optical and physical properties of plastic ophthalmic lenses
Corlon lenses
???
Manufacturing processes of plastics
The plastic is separate to two groups depend on the physical properties of the finished product
1- Thermoplastic Materials
these soften when heated and therefore can be remolded.
2- thermosetting Materials
Once hardened, these plastics can not be softened, even at high temperatures.
compare plastic and Glass lenses
plastic lenses
1/2
weight
of glass
highly
impact-
resistant.
With a CT of 3.0mm w/o special hardening process.
thicker
profile than glass,
get
scratches
more easily
No UV
protection unless properly tinted.
Glass lenses unlike plastic, must be treated to resist
breakage
(chemical or heat)
Plastic materials
Original plastic lens made
(The primary commercial product is known as organic glass.)
WW II glass was used for submarine and airplanes.
The spectator protection in ice hockey rinks is made from PMMA.
Advantages
1- CR-39 has a half
weigh
t of ophthalmic crown glass with similar prescription and of identical size
2- they are fairly
impact resistant
in their natural state
3- CR-39 are very inert and are resistant to almost all
solvent
and chemicals except perhaps, highly oxidizing chemicals
4- CR-39 is less prone to
fogging
than glass
5- CR-39 has much
lower thermal conductivity
than glass
6- Cr-39 lenses can be
tinted
to almost any color
7- reduces the manufacturing
price
than glass forms as a result of the material nature.
Disadvantages
1- it is soft and easy to
scratches
2-
thicker
than crown glass the has the same power
3-
although it have fairly
low refractive index
They have
inferior photo-chromic
qualities when compared with glass lenses

1- it is a specific type of lens made from plastic and glass lens
2- the front is glass and the back is plastic
3- these lenses are manufactured as C-Lite lenses.
The advantage
1- it is 25% thinner than conventional lenses.
2- it is 25% lighter than all-glass lenses.
Take home msg
(PMMA)
(CR 39)
Polycarbonates
Optical and physical properties of plastic ophthalmic
(CR 39)
Corlon lenses
Manufacturing processes of plastics
Thermoplastic Materials
Thermosetting Materials
made from two different materials
1. poly(methyl methacrylate) (PMMA)
which is harder and more
resistant to scratches
than other plastic lens materials.
Plastic lenses are made from a
very high quality
material as glass.
2. Modern hard resin lens from ally1 diglycol carbonate
(CR 39)

Advantages
1- they are vastly superior to ophthalmic glass and CR-39 in term of
impact resistant
2- it have
high R.I
(1.586)slightly higher than the ophthalmic crown glass.
3- it have a
specific gravity
of 1.20 (as compared with 1.32 for CR-39) and therefore lenses made of this material is the
lightest
spectacle lenses in production
4- these lenses are easily
tented
and an
abrasion resistant coating
which also absorbs
UV
radiation is applied to both front and back surface.

Disadvantages
1- it has a
low Abbe value
and hence gives rise to a higher amount of
chromatic dispersion
than glass or Cr-39
2- the surfaces of polycarbonate lenses are difficult to mold to
completely eliminated imperfections
.

it is called the injection molding
When the thermoplastic heated, it is stretched, pressed or molded into complex shapes with no apparent chemical change
When it is cooled, it is retain the shape of the container in which there were heated
Example: Plexiglas, Lucite, PMMA, cellulose,…etc
1- manufacturing of Thermoplastic

The manufacturing process distinguishing factor from the
injection molding processing
is that the hardening of thermosetting materials is an
irreversible
process.
Example: epoxy resins, phenolics (Bakelite) and CR-39 (diglycol carbonate).
2- manufacturing of Thermosetting
Video
CR39 type
Polycarbonates
Full transcript