The common Faults in opthalmic lens.

This presentation mainly deals with the common faults in opthalmic lens and also briefly about the method to identifying the faults.

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1Made by : Abin Mathew
Presenting by: Sudhina,Anoushka
2nd year optometry students
From:SIMS&RC
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It is the portion of the transparent medium
bounded by two refracting surfaces of at least one
of which is curved.
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3. INTRODUCTION •In the context of opthalmic lenses,faults
refers to the defects or imperfections that
may affect the performance or quality of the
lens
•Fault is a defect before manufacturing or after
manufacturing
•Fault may be affect image quality & visual
comfort
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4. FAULT
A len fault refers to imperfections or defect in lens that negatively
affect its preformance
This includes various issues such as scratches,cracks,or distortion
on the lens surface
This may result in blurred or distorted Image
Lens Fault can impact image quality and may require replacement
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5. CLASSIFICATION
FAULTS
DEFECTS BY MANUFACTURING SURFACE DEFECTS ERRORS IN POWER OF THE LENS
i.Colour
ii.Strain
iii.Bad metal
iv.Bubbles
v.Feathers
vi.Veins
vii.Cloudiness
i.Pits or holes
ii.Grey
iii.Polishing burn
iv.Waves or rings
v.Orange peel defects
vi.Generators marks
i.Lab tool errors
ii.Excessive blocking pressure
iii.Inconsistent base curve
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6. A.DEFECTS BY MANUFACTURING
Now a days due to technological advancement such manufacturing
defects are very rare
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A colour defect in lens can manifest as chromatic
aberration where different wavelengths of light
are focused at different distances
Generally arises if impure material is not
removed during manufacturing process
This can distort the image Quality and affect
clarity
Eg: Any stress of iron oxide in silica causes unwanted green
colour
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For reference
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A strain defect in lens refers to any deformation or
stress within the lens material itself
It is usually caused if molten glass is allowed to cooled
rapidly
Can occurs during manufacturing,handling or use
The can cause various issues such as blurring,distortion
and aberrations in image produce by the lens
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9. Bubble defect in lens occurs when air bubbles or pockets
are trapped within the lens material during
manufacturing process (gaseous matter which does not escape from lens
before glass cool)
This defect occurs during melting and fining process
Mainly barium crown and flint glass are very prone to
this defect
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‣A material defect in a lens refers to any
flaw, imperfection, or irregularity in the
material composition of the lens glass or
coating.
‣Material defects can degrade the
performance and image quality of the
lens, necessitating repair or replacement
to restore optimal functionality.
‣In simple words,these are foreign body
or particle remains in glass
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‣Cloudiness in a lens typically refers to a
condition where the glass appears hazy or
milky, affecting image clarity and quality.
‣This defect can be caused by various factors
such as internal condensation, contamination,
or manufacturing imperfections.
‣In severe cases, it may require professional
cleaning or even lens replacement to restore
clarity and functionality.
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‣Veins in a lens are a type of defect characterized
by thin, thread-like pattern's visible within the
glass.
‣ can occur due to irregularities in the
manufacturing process or impurities within the
lens material.
‣ Veins can adversely affect optical performance by
causing light scattering or distortion, leading to
reduced image quality and clarity.
‣Depending on their severity, veins may require
repair or replacement.
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‣These are clusters / group of bubbles.
‣This is usually seen around bad
material which gives an appearance of
small feathers in glass
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12. B.SURFACE DEFECT
These faults usually present on the surface of lens
Caused by inadequate polishing or improper handling of lens
These defect can affect the clarity,Quality and performance of the lens
potentially causing distortion,aberration or reduced optical performance
These include pits or holes,grey,polishing burn,waves or ring,orange peel defects etc.

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It usually caused frequently,when insufficient
smoothing process takes place on the grinding
machine
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During polishing if the lens surface is allowed
or get too hot
If it lack the lubrication between polishing pad
and lens , the polishing burn can occures
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It is a form of defect when unwanted chances
in curvature occurs
It is an undeviation and ripple on lens surface
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‣As name suggest it is look like peel of orange so defect
is also called orange peel defect
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‣It is caused by incomplete
polishing of the lens blank
‣After incomplete polishing is
done surface appear to be grey
in colour
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‣Generator marks are parallel,curved mark
across the surface of the lens ,caused by
generator marks.
‣Light generator marks are normal after
generating,after fining and polishing they
should not be visible.
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18. C.ERRORS IN POWER OF LENS
These errors are produced while entering power to the lens.
These includes;
i. lab tool errors
ii.Excessive blocking pressure
iii. Inconsistent base curve

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19. HOW TO IDENTIFY DEFECT ?
I.By looking directly through the lens : TRANSMISSION (T)
II.By using the technique: SHADOWING(S)
III.View the light reflection from the lens surface: REFLECTION (R)
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๏There are three methods for identifying defect
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BAD METAL VEINS HOLE
BUBBLES Colour GREYNESS
FEATHERS WAVES SCRATCH
POLISHING BURN RING DIG
WAVES ORANGE PEEL ABUSES MARK
RINGS
STRAIN
SLEEK
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