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OPHTHALMIC MATERIALS > GUNTER > Flashcards

GUNTER Flashcards

1
Q

NATURAL FRAME MATERIALS

A
  • “real shell”
  • horn (buffalo)
  • wood
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2
Q

WOOD FRAMES

A

can split + warp

difficult to glaze - doesn’t stretch

absorbs water + sweat if coating damaged

can be adjusted with great difficult - dry heat can crack it

more stable if laminated

many woods are toxic or carcinogenic

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3
Q

WHICH NATURAL FRAME MATERIAL CAN NO LONGER BE OBTAINED NEW + WHY?

A

“real shell”

it’s the carapace (shell) of the hawksbill turtle + it’s illegal to kill them anywhere in world - protected

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4
Q

THERMOPLASTIC

A

goes soft when heated + hard when cooled

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5
Q

THERMOSETTING

A

becomes hard or solid when heat is applied + remains that way on being re-cooled

change is not reversible

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6
Q

ACRYLATES/ ACRYLICS

A

thermoplastic - high softening temperature

easily broken

usually supras

claimed hypoallergenic

never yellows with age

no reinforcing wire inside

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7
Q

CELLULOSE ACETATE

A

thermoplastic

light/ strong/ cheap/ hard ISH

good colour range

can be made in layers to give shell effect

pads sometimes stuck on with acetone

almost always have reinforcing wire in side

half joint attached to front by heat/ ultrasonic insertion + attached to side by soldering

hypoallergenic in pure form but never used in this form

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8
Q

WHAT TEMPERATURE DOES ACETATE SOFTEN AT?

A

56 degrees

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9
Q

WHY IS CELLULOSE NITRATE BANNED IN UK?

A

it’s flammability

ignition point + softening point are very close

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10
Q

CELLULOSE NITRATE

A

made by routing (cut from sheet with spinning tool)

half joints always riveted to front + sides

if clear, turns yellow + crystallises with age

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11
Q

CELLULOSE PROPIONATE

A

very common thermoplastic

light/ strong/ cheap/ hard ISH

half joints always hear unsettled or screw-on lug on front

usually polyurethane lacquer coated

almost always surface coloured

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12
Q

EPOXY RESINS

A

thermosetting plastic

liquid monomers react in mould

claimed to be hypoallergenic

polyurethane coated - protects, reduces allergenic potential + facilitate surface dyeing

light material - little metal in most
epoxies used to coat metal frames

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13
Q

POLYAMIDES

A

large group of polymers

safety/ sports/ toddler frames
sunglasses

low density, can be strong

shrink when heated (usually
glazed cold)

usually made by moulding

can be coated with lacquer

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14
Q

POLYCARBONATE

A

best known as a lens material

strong + light

often used for sunglasses + side shields on safety specs

very high softening temp

surface dissolves in acetone if not lacquered

no side reinforcement

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15
Q

SILICONE RUBBERS

A

nose pads, bridges + side tips on metal frames

non-adjustable

soft, flexible material

usually have acetate cores

extremely stable + retain their elastic properties from -50 to 200 degrees

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16
Q

LIQUID/ GEL SILICONES

A

pads on metal frames

in a silicone rubber envelope

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17
Q

FLEXIBLE POLY-VINYL CHLORIDE (F-PVC)

A

majority of pads on metal frames

not sticky to touch

semi-soft

often have acetate or metal cores

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18
Q

COMPOSITES

A

fine, strong fibres set in another plastic

cracks have to go round the fibres before frame breaks

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19
Q

CARBON FIBRE

A

best known composite

mostly nylon

fibre just adds strength

always grey/black

surface often has coloured lacquer

most have closing block to secure lens

20
Q

KEVLAR

A

long chain polyaramides

composite

softens in a frame heater

21
Q

ROUTING

A

process in which sheets of material have the excess cut away to form the frame with a “routing” machine

22
Q

WHICH PLASTIC ARE MOST OF PADS ON METAL FRAMES MADE FROM?

A

silicone rubber

f-PVC + liquid/gel silicone

23
Q

WHAT IS IN A METAL FRAME TYPICAL STRUCTURE?

A

base metal, plating, organic coating + plastics/silicone fittings

24
Q

WORK HARDENING

A

aligns crystals in metals - makes harder + springier

can also make them more brittle

makes metal harder through plastic deformation

25
Q

SOLDERING

A

process in which two or more items are joined together by melting + putting a filler metal (solder) into the joint

filler metal has lower melting point

26
Q

WELDING

A

parts melted together +/or joined by similar material that melts into + alloys with the surface

single piece of meta when finished

melting point is a lot higher

27
Q

WHY CAN REPAIRING A METAL FRAME FROM SOLDERING OR WELDING CAUSE A PROBLEM?

A

metal can form a protective oxide quickly e.g. aluminium, titanium or stainless steel

28
Q

ALLOYS

A

most base metals + platings are allows

solution, not mixture of metals

29
Q

PLATING OF FRAMES

A

metal frames often played with another metal to improve cosmetic appearance + to reduce corrosion

30
Q

ELECTROPLATING

A

method where majority of metal frames are plated with gold + other metals

usually involves cyanide compounds so strictly controlled + can’t be done in most practices

31
Q

CHEMICAL DEPOSITION

A

used to repair plating after solder repairs

how plastics are metal plated

32
Q

ROLLED GOLD

A

plating method

not legal to sell gold filled in UK

rolling process work-hardens wire + plating

33
Q

VACUUM COATING

A

plating method

metal evaporated in a vacuum + condense onto cold surface i.e. frame

can be done on almost any material

34
Q

PLASMA SPUTTERING

A

plating method

includes systems that use indirect heating with radio waves + other energy sources

often small amount of inert gas in chamber rather than vacuum

can be done on almost any material

35
Q

LACQUERING (POLYMER COATING) PURPOSE

A

gives colour

prevents corrosion

prevent (often dangerous) metal jobs contacting the skin

36
Q

WHAT MAKES A BATTERY?

A

plating + base metal + body fluids

base metal corrodes under plating metals + plating lifts off

37
Q

ALUMINIUM

A

light, soft, safe

often thick because soft

often anodised

38
Q

NICKEL

A

toxic, allergenic, carcinogenic

in majority of specs

cheap, easy to solder or weld, easy to plate + usually doesn’t corrode

39
Q

TITANIUM

A

light, strong

often nickel plated

almost never pure - even if anodised, surface is often dyed

40
Q

PLATING METALS

A

chromium

gold - almost always alloys

white gold - gold alloys

platinum group - expensive

nickel, copper

41
Q

HALLMARKING ACT 1973

A

only for gold, silver + platinum

cannot well in europe unless hallmarked

42
Q

WHAT CARAT IS PURE GOLD

A

99% = 24ct

43
Q

FOR WHICH COLOUR OF VISIBLE LIGHT IS THE REFRACTIVE INDEX OF OPHTHALMIC LENS MATERIALS HIGHEST?

A

blue - short wavelength

44
Q

WHAT TWO TERMS DESCRIBE DIFFERENT ASPECTS OF CHROMATIC ABERRATIONS?

WHICH ONE IS NOT AFFECTED BY APERTURE SIZE?

A

longitudinal + transverse

longitudinal not affected by aperture size

45
Q

SEIDAL ABERRATIONS

A

S1 - spherical aberration

S2 - coma

S3 - oblique astigmatism

S4 - field/ image curvature

S5 - distortion

46
Q

WHAT SEIDAL ABERRATION IS MOST IMPORTANT?

A

oblique astigmatism

relatively straightforward to reduce it

47
Q

PINCUSHION DISTORTION

A

the further from optical axis a point is, the more it is magnified

it affects positive powered lenses

OPHTHALMIC MATERIALS (4 decks)

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