8 - GP manufacturing

What are the steps in manufacturing a GP lens?

1. cutting and preparation of polymer

2. machining (cutting + polishing base curves, cutting + polishing front curve, finishing)

3. in-office modification

Who cuts and prepares the polymer?

polymer manufactures

How is polymer cut and prepared for CL use (steps)?

1. purity and quality of raw materials are evaluated

2. refrigerate material

3. tested for impurities using distillation

4. polymerization

What are the ways for the polymer material to be prepared?

1. rods

2. sheets

3. buttons

What shape of polymer is received by CL lab?

button

How is machining done?

almost always by lathe cutting

What is the downside to lathe cutting?

can be inconsistent because it is:

-produced with slow, shallow cuts

-needs constant application of liquid air coolant

Do GPs usually undergo machining or molding?

machining more common

What are the advantages of GP molding instead of machining?

1. eliminates inconsistencies

2. improvements in curing techniques needed to improve material stability

How does a GP undergo both machining and molding (combination)?

molded back surface

lathe front curve/power curve + lenticulars

What is the downside to high Dk in terms of manufacturing?

more difficult to manufacture:

-slower speeds

-slower polishing

-need to use reduced heat

What part of the RGP is cut first?

back surface

How do they make the back surface of the RGP?

cut a concave radius with a lathe

what is used to polish the base curve?

pitch

soft waxes

pellon pads

What step is taken after cutting and polishing the base curve?

verify base curve

What is the first step in making the front curve of a RGP?

mount button on an arbor with water soluble wax

Which curve makes up the RGP power?

front curve

When is the lens blanked reduced to its final thickness?

when making the front curve

When is lenticulation performed?

when cutting the front curves of the lens

What parts of the GP are verified?

1. BCR

2. Power

3. Edge + optics

4. Zone widths

5. Blend

6. CT

what are the strategies used to verify the GP?

1. checking every lens

2. statistical process control

what is statistical process control?

sampling and control of equipment → only a small # of lenses are selected and verified

What are the advantages to in-office modification of GPs?

faster for dr

faster for patient

Which lenses should not be modified in office?

1. high Dk lenses

2. lenses with plasma or other coatings

what are the surface coatings/treatments?

1. plasma

2. polyethylene glycol (PEG)

What is plasma?

highly excited ionized gas consisting of electrons

fourth state of matter

how is plasma handled?

materials are treated with cold plasma gas in a reaction chamber

shipped wet to practitioner

how does plasma coating affect GPs?

improved lubricity, wetting and bond strength

Why is plasma coating used on GPs?

1. removes residues from manufacturing process

2. increases wettability - decrease in wetting angle

3. helps adaptation period

What does PEG do for GPs?

coats the lens with mucin like (similar to tears) hydrophilic shell

Why is polyethylene glycol used in CLs?

improves surface wettability

How should you care for coated GPs?

use non-abrasive cleaner (no polish or Boston products) until 6 months → then can use abrasives