give information of fault in ophthalmic lenses

1. FAULT
MADE BY : SWATI PANARA
FROM : BHARTIMAIYA COLLEGE OF
OPTOMETRY
2nd YEAR 3rd SEMESTER

2. OPHTHALMIC LENS
 It is the portion of the transparent medium
bounded by two refracting surfaces of at
least one of which is curved.

3. FAULT
 Fault is a defect before manufacture or
after manufacture.

4. MANUFACTURING OF AN
OPTICAL GLASS
BATCH
PROCESS
CONTINOUS
FLOW
PROCESS

5. DEFECT
Defect in the
material of the
lens
Defect on the
surface of the
lens

6. DEFECT IN THE MATERIAL
OF THE LENS
By looking directly through the lens –
transmission (T)
By using the technique – shadowing (S)
Viewing the light reflected from the lens
surfaces – reflection (R)

7. TRANSMISSION SHADOWING REFLECTION

8. TRANSMISSION
BAD METAL
BUBBLE
FEATHERS

9. TRANSMISSION

10. BAD METAL
 Also known as “bad stock” or “stones”.
 The material must be free from any
inclusions or foreign particles that may
appear in generally due to portion of the
batch material remaining undissolved
during the melt.

11. BUBBLE
 Formed by the large volume of gas given
off during the melting period.
 size 1 mm diameter – seeds.
 They are as small as droplets in the glass.
 They are escaped and their escape is
promoted in the process of rapid stirring.

12. BUBBLE

13. FEATHERS
 A cluster of bubbles or seeds often around
bad metal takes on the appearance of a
small white feather in the glass.

14. SHADOWING
COLOUR
STRAIN
VEIN

15. VEIN
 Fine thread or streak of glass of slightly
different refractive index to the
surrounding glass caused usually by
stirring.
 like a thin empty tube running through the
glass.
 There are caused by the insufficient mixing
of bad metal

16. TYPES
CORD
STRIA

17. Two types:
a) Cord (S) – Heavy or pronounced veins.
b) Stria (S) – A very fine vein

18. COLOUR
 The medium from which a spectacle lens is
made have a high degree of clearness &
transparency
 The defect Color – is defined as any
unintended coloration in a medium which
is supposed to be white generally arises
from the use of impure materials in the
composition of the medium

19.  Any stress of iron oxide in silica, the
manufacturing glass causes unwanted
Green tinting.
 Certain high index material ingredients
will show slight yellowishness.
 Best detected on a matt white paper.

20. STRAIN
 If molten glasses allowed to cool too
rapidly the outer surfaces solidify before
the hotter inner portion. As the inner
portion then cools, it tends to shrink setting
up tension within the glass. The resulting
stress is called strain.
 May also arise if external forces are
allowed to compressed the glass.

21.  Glass may be inspected by means of
polariscope.
 The similar type of strain is seen if a tight
glazed glass is fitted in Frame.

22. DEFECT ON YHE SURFACE
OF THE LENS
Defects caused by
chemical or thermal action
During the production
Maltreatment of the
finished surface

23. DURING THE PRODUCTION
HOLE
GREYNESS
POLISHING BURN
WAVE
ORANGR PEEL DEFECT
GENERATOR MARK
RING
ROUNDING
CLOTHMARK
DRAG MARK
PAD MARK

24. HOLE (R)
 It is also called as PIT.
 A pit in the lens surface which may be
caused by breaking into a bubble, or more
frequently by insufficient smoothing.
 It can lead to drag marks.
 It can be caused by breaking into covers.

25. HOLE

26. GREYNESS (R)
 The appearance of a surface after
incomplete polishing.
The surface still appear smooth.
Polishing process should be continued until
all signs of greyness disappear.
 It appears to be grey

27. POLISHING BURN (T)
 Heat is generated during the polishing pad.
 It is very common defect.
 Appearance of transparent blister or group
of blister on surface.
 During polishing if the lens surface is
allowed to get too hot, then by lack of
lubrication between the polishing pad and
lens, the polishing burn of glisters can
occur.

28. WAVE (T) (S)
 A wave is a surface undulation or ripple,
the surface changing curvature in the
region of the wave.
 It indicates not only the nature of the
surfaces, but also the method by which
they were produced.
 Can be attributed to faulty machine motion
or by polishing on a badly smoothed
surface or even over polishing.

29. ORANGE PEEL DEFECT (S)
 A form of waviness' named after its
appearance usually extending over the
entire surface of the lens.
 A defect that is closely related to a wave is
called as orange peel defect.
 Some say that this type of surface is a
water polish.
 The defect is really a type of wave and
looks like the peel of a orange.

30. GENERATOR MARK
 The most common type of unwanted
patterned surface marks are generator
marks.
 Generator marks are parallel , curved
marks across the surface of the lens.

31.  They are caused by the generator wheel.
 Light generator marks are normal after
generating.

32.  After fining and polishing, they should
not be visible.
 If generator marks do not disappear after
fining and polishing it is usually because
of one of the three problems:

33. 1. A lap tool that does not match the curve
of the lens.
2. A generator that is cutting off curve
3. Incomplete fining

34. RING (T) (S)
 concentric waves produced on a spherical
surface.

35. RING

36. CLOTH MARK
the weave of the polishing pad on the lens
surface.
 Found on badly polished toroidal surfaces,
the surface appearing to have a diamond
shaped pattern following the base curve
meridian.

37. ROUNDING (S)
 A defect of figure at the edge of a lens
generally caused by excessive pressure
from a soft polishing pad towards the edge
of the lens.

38. DRAG MARK (S)
 A local wave usually associated with an
edge chip, the drag mark extending from
the chip & following the machine motion.

39. PAD MARK
 Can be experienced the form of the wave
duplicating the surface of the pad.

40. DEFECT CAUSED BY
CHEMICAL OR THERMAL
ACTION
CRASING
TARNISH

41. CRAZING (R)
 presenting the appearance of criss-cross
cracks in the surface.
 Usually caused in GLASS by sudden
chilling but in PLASTIC lenses it results
either from stress or solvent action.

42. Criss cross cracks-
surface

43. TARNISH (R)
 Chemical chances at the surface of the
lens, brought about by extreme
atmospheric conditions
 Flint glasses are particularly prone to this
defects
 Chemical changes at the surface.

44.  Lead in the material gets oxidized and lead
oxide is formed thus giving yellowish
colour
 High index lenses are particularly prone to
tarnish

45. MALTREATMENT OF THE
FINISHED SURFACE
SCRATCH DIG SLEEK
BRUISE
CHECK
CHIP

46. SCRATCH
 It may be found at any stage in the
grinding process.
 Elongated penetration on the surface with
jugged edge.

47. SCRATCH

48. CAUSED BY
 Penetration of surfaces characterized by
sharp edges
 Incorrect handling
 Contamination of polishing liquid
 Splintering of material.

49. DIG (R)
 A short scratch usually caused by striking
the lens with a sharp object or as a result of
dropping the lens.

50. SLEEK (R)
 an elongated penetration of the surface
without producing jagged edges.
 It may occur if a lens is cleaned with a
rough or dirty cloth.

51. CHIP (R)
 it occur at the edge of A Lens produced
either by impact on the edge or by tension
being applied by a spectacle frame.

52. BRUISE CHECK (R)
 it is a surface crack or fracture due to
impact on the surface of the glass.
 Crescent shape incomplete.

53. ABUSE MARK
 Term applied to cover surface defect
caused by bad handle.

54. NO TRANSMISSION
[T]
SHADOWING
[S]
REFLECTION
[R]
1. BAD METAL VEINS TARNISH
2. BUBBLES CORD CRAZING
3. FEATHERS STRIA HOLE
4. POLISHING
BURN
CLOTH
MARKS
GREYNESS
5. WAVES WAVES SCRATCH
6. RINGS RINGS DIG
7. DRAG
MARKS
SLEEK
8. ORANGE
PEAL
BRUISE
CHECK
9. ROUNDING CHIPS
10. ABUSE
MARKS

55. THANK
YOU