OPTOMETRY

1. Quality Assurance and
Inspection of CL

2. Quality Assurance and Inspection
 This is an important step and the inspection is performed of every lens
prior to packaging and distribution

3. Sterilization
 The lenses are sterilized before dispensing. The method mostly employed
is autoclaving. The lenses are autoclaved at a temperature of 124 degrees
celsius for at least 20 minutes.

4. RGP Manufacturing
RGP lenses are manufacture by 2 methods:
 • Lathing—used commonly
 • Molding—recently adapted technique.

5. Tinting of RGP Lenses
 To tint a RGP lens the dye is dissolved in the monomer before mixing and
polymerization.

6. Soft Contact Lens Manufacturing
 Soft lenses can be manufactured by following methods:
 • Molding
 • Spin casting
 • Lathing
 • Molding /lathing combination
 • Spin casting lathing combination
 • Molding—stabilized soft technique

7.  Molding /lathing combination: Usually the back surface is molded and the
front surface is lathed.
 Spin casting/ lathing combination: Usually the front surface is spin cast
and the back surface is lathed
 Stabilized soft molding: A space taking inert diluent is included in the mix
of monomers during polymerization
This diluent is replaced by water later.
The final product thus achieved thus undergoes minimal change on hydration
and provided high quality optics and surface finish.

8. CONTACT LENS VERIFICATION
 The contact lens once ordered should be verified before dispensing.
 Though the laboratories try to maintain standards, yet there are
possibilities and errors, which are due to the manufacturing.
 A faulty lens will not conform to the design specially ordered.

9. The following parameters, which need
to be verified, are:
 1. Base curve
 2. Power
 3. Diameter
 4. Central thickness
 5. Surface quality
 6. Edge
 7. Blend
 8. Material

10. Base Curve
 Radiuscope
 Keratometer

11. Radiuscope
 The Radiuscope is the most commonly used instrument in the laboratory
to verify the base curve.
 It is based on the Drysdale’s principle.
 The lens RGP (in dry state- soaked 24 hrs before) and the soft lens (in wet
cell with 0.9% saline) is kept with concave side up on the lens mount.
 The first focal plane mires are focused, the reading is set at zero at this
position. The dial is further moved to focus the second set of mires, which
is the second focal point. The distance between the two focal points
measures the radius of curvature, which is read from the dial.

12.  In case of a toric lens the mires will have two set of lines perpendicular to
each other, which will be focused separately. A warped lens will show no
definite base curve.
 The Keratometer can also be used to verify the base curve, though not
very accurate.
 The set up is modified with the lens holder and a mirror attachment. The
lens is held with the help of this holder and the readings taken same ways
the Keratometer is used.

13. Radiuscope

14. POWER VERIFICATION
 Focimeter/Lensometer
 This instrument is used exactly as for the spectacle lens.
 The contact lens is cleaned first and then centered concave side down on
the focimeter stop.
 Read the values on the drum.
 The prism can also be measured the same way as in spectacle lenses.
 The lens power should be within +/– 0.25 D of the power ordered.

15. Focimeter/Lensometer

16. Lens on focimeter
 In case of toric lenses two line focuses will be obtained. The two principal
meridians are noted and then transposed to read the spherical and the
cylindrical values.

17. Diameter
The V sought gauge
 or the measuring loupe can verify the diameter of the RGP lens.
 The lens is made to slide across the V slought and allowed to fall into the
proper position by its own weight. Note the reading in millimeter
corresponding on the scale.
 While measuring ensure that the:
 Lens is dry
 Take care not to exercise any force while inserting the lens into the gauge
 Check in two meridians for roundness
 The tolerance limit is +/–0.05 mm

18. V slought gauge

19.  The measuring magnifier—the lens is held across the magnifier and the
scale reading of the diameter are correspondingly read.
 This also serves the dual purpose of measuring the diameter and the width
of the peripheral and the optic zone.
 The soft lens analyzer or the projection devices in wet state can also
measure the soft lens diameter.

20. Central Thickness
 The thickness gauge or the dial gauge is the most useful device for
measuring central thickness
 . The lens is placed convex side down on its base.
 A spring plunger tip is released until it touches the lens.
 The thickness is read directly on the gauge. Ensure the zero error before
hand.

21. Surface Quality
 Various types of projection devices available can measure the surface
quality and the edge profile.
 The projection analyzer can also be used to measure the optic zone
diameter and the peripheral curves width.
 The surface can also be inspected by use of slit lamp. Use monochromatic
light and inspect the lens

22. Blend and Edge Shape
 The projection analyzer or the magnifying loupe is used to examine the
transition zones of the peripheral curves.
 Edge is most important for the comfort of the RGP lens. The faulty lens
can create problems, so it is essential to inspect the lens edge of an
uncomfortable lens.
 The lens can be held; with the help of a holder, and the image of the lens
edge can be created on the wall by holding the lens in the slit-lamp
illumination.
 As discussed earlier the round edge is the most comfortable one.

23. Edge examination with magnifier

24. Material
 All Rigid materials look same but have a fixed specific gravity. The material
can be verified by testing its specific gravity.
 Different solutions bottles with known specific gravity are needed. The
lens is dipped in the bottles one by one.
 The specific gravity can be calculated if it floats or sinks in the known
specific gravity.

25. Verification of Parameters—Summary
 • Base curve—Radiuscope
 • Diameter—V slought gauge
 • Power—Lensometer
 • Central thickness—Dial gauge
 • Peripheral curves/width/blend—Projection analyzer or magnifying loupe
 • Material—Specific gravity test.

26. THANK YOU