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RAJU KAITI
Optometrist, Dhulikhel Hospital, Kathmandu
University Hospital
 Checking quality and physical characteristics
for-
 Prescription use
 Contact lens fitting sets
 Research purposes
 ...
 Laboratory
 During the final phase of manufacture, an overall parameter
check is performed to ensure the lenses do not ...
 Ensure correct lens is dispensed
 Quality of manufacturing(as per quality standard)
 Assess changes in contact lens wi...
 Rigid and soft lenses have similar parameters which
require verification by the practitioner.
 Radii of curvature
 Lin...
 Back optic zone radius
 Back central optic zone radius
 Back peripheral optic zone radius
 Front optic zone radius
 ...
 Back optic zone diameter
 Back central optic zone diameter
 Back peripheral optic zone diameter
 Front optic zone dia...
 Central
 Edge
 Lenticular junction
 At any other specified point
 Axial and radial edge lift
 Edge shapes
 Back vertex power
 Front vertex power
 Near addition
 Prism and base direction
 Cylinder power
 Aberration
 Finish
 Polish
 Edge form
 Transitions
 Tint
 Material
 Radiuscope
 Keratometer (modified)
 Toposcope
 Moiré fringe deflectometer
 Radius checking device
 Topographical ma...
Drysdale’s principle
 Lens holder is filled with water
 Clean lens is placed centrally on holder, convex surface is in
complete contact with ...
 Dial gauge reading is recorded
 Second focus at centre of curvature of surface is obtained
 Second reading is recorded...
• Lens is measured in the dry state
• Front surface image eliminated with saline in lens mount
• Lens is centered concave ...
 same procedure for
determining the FOZR,except
that the lens is centered
convex side up on the
appropriate lens mount.
...
 Air checking, which requires
the SCL to be dabbed with a lint-
free cloth and measured in a
semi-dehydrated state.
 The...
 The Keratometer which is used for measuring corneal
curvature can also be used to measure the BOZR of a
contact lens by ...
 Keratometer set-up is
modified with a lens holder
and prism or mirror
attachment
 Values derived are less than
the actu...
 Keratometer set-up is modified
with a wet cell and prism or
mirror attachment
 Values derived are less than
the actual ...
The principle of the thick lens
system to design the R-C Device
whose refractive index is the same
as the lens material.
T...
By combining the features of the photokeratoscope and a
built-in camera, polaroid images of the cornea are captured
and vi...
 Back vertex power (BVP)
 Front vertex power (FVP)
 Front and back surface radii of
curvature.
 Centre thickness.
 Re...
 It measures BVP
 Projection focimeter-greater accuracy
 Nakijama-mounted lens in liquid cell and read power
of resulta...
 BVP in air is not equal to BVP in liquid
 If F1=BVP in air
 F2=BVP in liquid
 F1=kF2where k is compensation factor
 ...
 Lens is cleaned and dried
 Lens must be centered concave side down on the
focimeter stop
 Reading is taken off the pow...
 Power for each meridian is measured
 Cylinder value is derived from measuring the
difference in meridional powers
 The SCL is measured by air-checking it with the focimeter.
 The lens is dabbed with a lint-free cloth/tissue to remove
...
 Procedure is same as for BVP but with lens convex
side down
 FVP measurements can be converted to BVP by using
a table ...
 Lens diameters
 back optic zone diameter (BOZD)
 total diameter
 peripheral curve width (PCW)
 Lens thickness
 cent...
 Diameters and linear
parameters
 Measuring magnifier
 V gauze
 Cast, dividers and
transparent rule
 Micrometer & sph...
V gauze
Scale 6.00 – 12.50mm
Cast, dividers and
transparent rule
Micrometer
& spheres:
Measure
primary optic
diameter, sag...
 Can be measured with all most all techniques
 Indirect method:
 Thickness verification
 Dial thickness gauze
 Contek edge thickness
gauze & computer
 Radial thickness:
perpendicular...
 Lens diameters
 total diameter
 FOZD
 Lens thickness
 centre thickness (ct)
 edge thickness
 Instruments:
 Projection magnifier
 Moiré fringe deflectometer
 10x loupe with graticule
 Electronic thickness gauge...
Instruments/techniques:
• Edge molding
• Projection magnifier
• Ehrmann profilometer
• Palm test
• Radiuscope (modified)
 Surface defects
 Optical quality
 Lens impurities/deposits
 Scratches and lathe marks:
 Can cause:
 deposit build up
 poor wettability
 surface hydrophobicity
 Indicate over p...
 Instruments:
 Magnifying 10x loupe
 Projection magnifier
 Contact lens optical quality analyzer (CLOQA)
 Dark field ...
 White background test
 Variation in thickness
 Hydrogel contact lenses are flexible
 If exposed to atmosphere, they dehydrate and
alter their contour. Verification in...
 Mandell 1974 recommend following procedure-
 Lens should be removed from its liquid using sterile spatula or soft
plast...
 %water content = mass of watermass of hydrated lens x 100
 Water content of Hydrogel contact lenses is measured by
sens...
 On-eye-examination of
dispensing lens
 VA assessment before and
after over-refraction.
 Always assess
 dynamic and st...
 At the end of the verification process, the real
indicator that an accurate and optimal fitting
has been achieved is eva...
 Ensure that contact lenses dispensed have the
correct parameters, are sterile and in good
condition.
 Ensure that optim...
THANK
Contact lens verification(raju)
Contact lens verification(raju)
Contact lens verification(raju)
Contact lens verification(raju)
Contact lens verification(raju)
Contact lens verification(raju)
Contact lens verification(raju)
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Contact lens verification(raju)

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Contact lens Verification- different techniques

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Contact lens verification(raju)

  1. 1. RAJU KAITI Optometrist, Dhulikhel Hospital, Kathmandu University Hospital
  2. 2.  Checking quality and physical characteristics for-  Prescription use  Contact lens fitting sets  Research purposes  Contact lens verification undergoes two stages, laboratory and clinical.
  3. 3.  Laboratory  During the final phase of manufacture, an overall parameter check is performed to ensure the lenses do not differ significantly from the parameters ordered by the practitioner.  Clinics  Verification of lenses upon receipt, rather than during the dispensing visit, is advisable.  Patients  ‘on-eye’ fit is another indicator of whether a contact lens has been manufactured to specifications.
  4. 4.  Ensure correct lens is dispensed  Quality of manufacturing(as per quality standard)  Assess changes in contact lens with wear  To ensure that proper over-refraction and trial fitting examination has been conducted, the accuracy of trial sets used in the clinic should be determined.
  5. 5.  Rigid and soft lenses have similar parameters which require verification by the practitioner.  Radii of curvature  Linear parameters  Edge profile  Power  Lens quality  Rigid and soft contact lenses should be hydrated in a soaking solution for 12 - 24 hours before verification procedures are conducted.
  6. 6.  Back optic zone radius  Back central optic zone radius  Back peripheral optic zone radius  Front optic zone radius  Front central optic zone radius  Front peripheral optic zone radius
  7. 7.  Back optic zone diameter  Back central optic zone diameter  Back peripheral optic zone diameter  Front optic zone diameter  Front peripheral optic zone diameter  Total diameter  Bifocal segment size and position
  8. 8.  Central  Edge  Lenticular junction  At any other specified point
  9. 9.  Axial and radial edge lift  Edge shapes
  10. 10.  Back vertex power  Front vertex power  Near addition  Prism and base direction  Cylinder power  Aberration
  11. 11.  Finish  Polish  Edge form  Transitions  Tint  Material
  12. 12.  Radiuscope  Keratometer (modified)  Toposcope  Moiré fringe deflectometer  Radius checking device  Topographical mapping system  Electrical conductivity method  Microspherometer
  13. 13. Drysdale’s principle
  14. 14.  Lens holder is filled with water  Clean lens is placed centrally on holder, convex surface is in complete contact with water  Holder is placed on microscope stage and centered  Microscope eyepiece is correctly adjusted  By observing through microscope, target is imaged on surface of lens
  15. 15.  Dial gauge reading is recorded  Second focus at centre of curvature of surface is obtained  Second reading is recorded  Difference between two dial gauge reading gives radius of curvature of surface  Procedure is repeated twice and average of 3 reading is taken  Radius is measured in different point of lens as it may vary
  16. 16. • Lens is measured in the dry state • Front surface image eliminated with saline in lens mount • Lens is centered concave side-up • BOZR=distance between1st and 2nd focal plane
  17. 17.  same procedure for determining the FOZR,except that the lens is centered convex side up on the appropriate lens mount.  The scale is reversed so that the aerial image will be focused before the real image.
  18. 18.  Air checking, which requires the SCL to be dabbed with a lint- free cloth and measured in a semi-dehydrated state.  The critical duration of such air- checking is approximately one minute depending on ambient temperature and humidity.  Requires a wet cell filled with saline solution  The readings are multiplied by the refractive index of saline to calculate the BOZR IMMERSION
  19. 19.  The Keratometer which is used for measuring corneal curvature can also be used to measure the BOZR of a contact lens by using special attachments.
  20. 20.  Keratometer set-up is modified with a lens holder and prism or mirror attachment  Values derived are less than the actual radii  The same procedure for measuring the cornea is used for contact lenses
  21. 21.  Keratometer set-up is modified with a wet cell and prism or mirror attachment  Values derived are less than the actual radii  Readings are multiplied by the RI of saline to get the BOZR  The same procedure for measuring the cornea is used for contact lenses
  22. 22. The principle of the thick lens system to design the R-C Device whose refractive index is the same as the lens material. The contact lens floats on a liquid interface which has the same refractive index as the lens material. The R-C device is used in conjunction with the focimeter and lens thickness gauge.
  23. 23. By combining the features of the photokeratoscope and a built-in camera, polaroid images of the cornea are captured and viewed with a computer monitor.
  24. 24.  Back vertex power (BVP)  Front vertex power (FVP)  Front and back surface radii of curvature.  Centre thickness.  Refractive index.
  25. 25.  It measures BVP  Projection focimeter-greater accuracy  Nakijama-mounted lens in liquid cell and read power of resultant contact lens-liquid lens on projection focimeterBVP of soft contact lens can be measured in air or liquid  Clarity of focimeter image relates to optical quality of lenses
  26. 26.  BVP in air is not equal to BVP in liquid  If F1=BVP in air  F2=BVP in liquid  F1=kF2where k is compensation factor  K=n2-n/n2-n1 where,  n=refractive index of air  ,n1=RI of saline  .n2=refractive index of Hydrogel material
  27. 27.  Lens is cleaned and dried  Lens must be centered concave side down on the focimeter stop  Reading is taken off the power drum/scale after focusing the mires  Back vertex focal length is measured from the plane of the focimeter stop
  28. 28.  Power for each meridian is measured  Cylinder value is derived from measuring the difference in meridional powers
  29. 29.  The SCL is measured by air-checking it with the focimeter.  The lens is dabbed with a lint-free cloth/tissue to remove excess water.  The SCL is centered on the focimeter support and the procedure used to measure RGP lenses is followed.  An SCL can also be measured by immersing the lens in saline contained in a wet cell. Because the lens power is measured in saline, the value has to be multiplied by four (approximately) to calculate the true lens power in air.
  30. 30.  Procedure is same as for BVP but with lens convex side down  FVP measurements can be converted to BVP by using a table with known center thickness and back optic zone radius
  31. 31.  Lens diameters  back optic zone diameter (BOZD)  total diameter  peripheral curve width (PCW)  Lens thickness  centre thickness (ct)  edge thickness
  32. 32.  Diameters and linear parameters  Measuring magnifier  V gauze  Cast, dividers and transparent rule  Micrometer & spheres Measuring magnifier 20 mm scale: used for corneal lens
  33. 33. V gauze Scale 6.00 – 12.50mm Cast, dividers and transparent rule Micrometer & spheres: Measure primary optic diameter, sag is determined
  34. 34.  Can be measured with all most all techniques  Indirect method:
  35. 35.  Thickness verification  Dial thickness gauze  Contek edge thickness gauze & computer  Radial thickness: perpendicular to front surface of lens  Axial thickness: parallel to primary axis of lens  Spectacle lens measure  Radiuscope: no water used Thickness gauze Contek edge thickness gauze & computer
  36. 36.  Lens diameters  total diameter  FOZD  Lens thickness  centre thickness (ct)  edge thickness
  37. 37.  Instruments:  Projection magnifier  Moiré fringe deflectometer  10x loupe with graticule  Electronic thickness gauge  Pressure controlled gauge  Electrical thickness gauge  Radiuscope (modified)
  38. 38. Instruments/techniques: • Edge molding • Projection magnifier • Ehrmann profilometer • Palm test • Radiuscope (modified)
  39. 39.  Surface defects  Optical quality  Lens impurities/deposits
  40. 40.  Scratches and lathe marks:  Can cause:  deposit build up  poor wettability  surface hydrophobicity  Indicate over polishing during manufacture
  41. 41.  Instruments:  Magnifying 10x loupe  Projection magnifier  Contact lens optical quality analyzer (CLOQA)  Dark field microscope  Moire fringe deflectometer
  42. 42.  White background test  Variation in thickness
  43. 43.  Hydrogel contact lenses are flexible  If exposed to atmosphere, they dehydrate and alter their contour. Verification in air is inaccurate due to-  Shrinkage of Hydrogel on dehydration  Accumulation of surface moisture  So, artifact liquid cells are used to measure parameters of soft lenses  But RGP lenses can be measured in air
  44. 44.  Mandell 1974 recommend following procedure-  Lens should be removed from its liquid using sterile spatula or soft plastics protected forceps  Lens is then placed on lint free tissue and tissue is folded over uppermost convex of lens  Both surface are blotted dry  Lens is dried in air with forceps  Lens surfaces are examined for smudges  It is preferable to check lens within one minute
  45. 45.  %water content = mass of watermass of hydrated lens x 100  Water content of Hydrogel contact lenses is measured by sensitive microbalance  Alternative methods-  Refractive index  Refractive indexes decreases as water content increases
  46. 46.  On-eye-examination of dispensing lens  VA assessment before and after over-refraction.  Always assess  dynamic and static fit,  surface wet ability & lens quality,  corneal integrity.
  47. 47.  At the end of the verification process, the real indicator that an accurate and optimal fitting has been achieved is evaluation of the lens in situ.
  48. 48.  Ensure that contact lenses dispensed have the correct parameters, are sterile and in good condition.  Ensure that optimum visual acuity is achieved by the patient with the contact lenses.  Ensure that the contact lenses fit satisfactorily.  Provide instruction on care and maintenance.
  49. 49. THANK

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