6_RGP+Examination+_26+CL+Manufacturing-Acc

What is done at the baseline examination for a new daily-wear RGP patient?

• Assess patient needs

• Perform comprehensive exam + fitting (empirical or diagnostic)

• Order lenses for dispensing at the next visit

What are the goals of the dispensing visit for a neophyte daily-wear RGP patient, and when does it occur?

• Occurs 1-2 weeks after baseline, as needed

• Assess lens fit and vision

• Teach insertion/removal

• If adjustments are needed: re-order lenses and schedule a new dispense visit

After successful RGP dispensing, how is early adaptation and follow-up managed?

• Patient should gradually build up wear time at home with goal of all-day wear

• At 1-2 week follow-up: assess fit, vision, comfort

• Ask about insertion/removal difficulties

• If needed: adjust, re-order, and re-dispense

What is the purpose of the longer-term follow-up schedule for daily-wear RGP neophytes?

• 1-3 month follow-up: assess lens adaptation, especially if concerns arose at dispense

• Especially useful in scleral lens patients to assess lens surface and cleaning

• 6 month follow-up: as needed

• Yearly exam: comprehensive exam, evaluate habitual lenses, and re-order or refit as needed

How do other RGP follow-up schedules generally compare with soft contact lens follow-up schedules?

They are similar to soft lens follow-up schedules, with follow-up visits tailored to monitor adaptation, lens performance, and ongoing lens care needs.

Why might patients wearing RGP lenses long-term need interim follow-up visits?

Because RGPs are often worn for ≥12 months, patients may need interim visits to:

• check for lens deposits

• clean lenses professionally if needed

• reinforce home care (e.g., Progent use at home)

How does proparacaine affect adaptation in new RGP wearers, and when should it be used?

Research suggests RGP wearers are more likely to adapt to lenses if proparacaine is used at the:

• fitting visit

• dispensing visit

How does RGP comfort compare with soft lenses after the initial adaptation period?

After about 2 weeks of wear, RGP lenses can be as comfortable as soft lenses.

What is the recommended RGP lens adaptation (wear-time build-up) schedule during the first week?

• Day 1-2: 4 hours

• Day 3-4: 6 hours

• Day 5-6: 8 hours

• Day 7+: 10 hours

How should a new RGP wearer increase daily wear time during adaptation?

Increase wear time gradually over the first week rather than starting with all-day wear:

• begin at 4 hours/day

• increase every 2 days

• reach about 10 hours/day by day 7+

What are the major steps in RGP lens manufacturing?

• Cutting and preparation of polymer

• Machining

  • cut/polish base curves

  • cut/polish front curve

• Finishing

• Possible in-office modification in some cases

What happens during polymer cutting and preparation in RGP lens manufacturing?

• Done by polymer manufacturers

• Purity and quality of raw materials are evaluated

• Material may be refrigerated

• Tested for impurities using distillation

• Then undergoes polymerization

What is the role of machining in RGP lens manufacturing?

• Base curves are cut and polished

• Front curve is cut and polished

• The front curve provides the appropriate lens power

In what forms is RGP/GP lens material prepared during polymerization, and what additional processing is done?

Material is prepared as:

• Rods

• Sheets

• Buttons
  It also undergoes annealing.

How is machining of GP lenses usually performed, and what factors can affect consistency?

• Usually done by lathe cutting

• Can be inconsistent because quality depends on:

  • slow, shallow cuts

  • constant application of liquid air coolant

How does molding compare with machining for GP lens production?

Some GP lenses are molded like soft contact lenses, which can:

• eliminate inconsistencies seen with machining

• require improved curing techniques to improve material stability

What is a combination approach to GP lens manufacturing?

A hybrid method uses:

• molded back surface

• lathe-cut front curve/power curve and lenticulars

How does higher Dk affect GP/RGP lens manufacturing?

Higher Dk materials are more difficult to manufacture.

What machining changes are needed for high-Dk GP materials?

High-Dk materials require:

• slower speeds

• slower polishing

• efforts to reduce heat

Why must heat be minimized when machining high-Dk GP lenses?

Because high-Dk materials are harder to manufacture and are more sensitive during machining, so slower cutting/polishing and reduced heat help preserve lens quality.

How are base curves made in GP/RGP lens manufacturing?

• A lathe is used to cut the concave radius (base curve)

• The surface is then polished

What materials/tools may be used for polishing base curves in GP/RGP lens manufacturing?

Polishing may use:

• Pitch

• Soft waxes

• Pellon pads

What happens during the unblocking step in GP/RGP lens manufacturing?

• The lens is removed from the tool/block

• The case is cleaned

• This is part of the finishing process before final inspection

What parameters are checked during quality control for GP lenses?

Quality control checks:

• BCR (base curve radius)

• Power

• Edge and optics

• Zone widths

• Blend

• CT (center thickness)

How is GP lens quality control typically performed, and what strategies do labs use?

• QC is often done by hand

• Labs may use:

  1. Check every lens

  2. Statistical Process Control (SPC) = sampling lenses + monitoring/control of equipment

What is the purpose of final edge polishing and inspection in GP lens manufacturing?

It is the final finishing step used to:

• polish the lens edge

• inspect the lens for final quality and accuracy

• ensure the lens is ready for dispensing

Why might a practitioner use in-office GP lens modification equipment, and who sells it?

• Contact Lens Manufacturer’s Association member laboratories sell the equipment

• Used because it is faster for you and faster for the patient

Which GP lenses should NOT be modified in-office?

Do not modify:

• High Dk lenses

• Lenses with plasma or other surface coatings

What are the main surface coatings/treatments mentioned for GP lenses?

• Plasma

• Polyethylene glycol (PEG)

How does plasma treatment work for GP lenses?

• Similar concept to soft contact lens surface treatment, but not as permanent

• Plasma is a highly excited ionized gas

• Considered the fourth state of matter

• Lens materials are treated with cold plasma gas in a reaction chamber

How are plasma-treated GP lenses shipped?

They are shipped wet to the practitioner.

What are the main manufacturing purposes of plasma treatment in GP lenses?

Plasma is used to clean contamination from substrates during manufacturing (e.g., metal, ceramic, glass, silicone).
Secondary benefits include:

• improved lubricity

• improved wetting

• increased bond strength

Why is plasma treatment used on GP lenses?

It helps by:

• removing remaining manufacturing residues

• creating a remarkably clean surface

• causing a large decrease in wetting angle

• improving on-eye wettability

What is the clinical effect of plasma on GP lens wettability, and how long does it last?

Plasma improves surface wettability/on-eye wettability, but the effect is short-term, lasting probably several weeks.

What is Hydra-PEG (polyethylene glycol, PEG) and what is its main effect on contact lenses?

What is Hydra-PEG (polyethylene glycol, PEG) and what is its main effect on contact lenses?

What types of contact lenses can be treated with Hydra-PEG (PEG)?

It can be applied to:

• soft lenses

• gas permeable (GP) lenses

How does the Hydra-PEG surface improve lens performance?

The 90% water surface polymer creates a mucin-like hydrophilic surface, which helps the lens better mimic the tear film and improves surface wetting/wettability.

How should plasma- and Hydra-PEG–treated GP lenses be cleaned initially?

Use a non-abrasive cleaner only.

• No polish in lab

• No Boston products, except Boston Simplus

When can abrasive cleaners be used on plasma- or Hydra-PEG–treated GP lenses?

After about ~6 months, you may use:

• Boston products and/or

• other abrasive cleaners

What is LipoCoat/Lipidure, and what is its main purpose as a lens coating?

A phosphorylcholine-based surface coating that mimics the tear film lipid bilayer/cell membrane, helping create a hydration layer and improve lens moisture/comfort.

What are the proposed benefits of LipoCoat/Lipidure on contact lenses?

• Tear-film–mimicking lipid-bilayer coating

• Helps keep lenses moist via hydrophilic modification

• May improve all-day comfort

• Can help repel deposits/proteins/cells and reduce surface adhesion

Historically, what type of soft contact lenses were the first FDA-approved, and what surface did they produce?

They were spin-cast lenses, which produced aspheric back surfaces.

What are the two modern methods of hydrogel contact lens manufacturing?

• Disposable lenses (daily, 2-week, monthly) → usually molded

• Custom/planned replacement lenses (quarterly/annually) → usually lathe cut and polished

What is the manufacturing exception for extended range (XR) hydrogel lenses?

XR lenses are an exception because they are often:

• back molded

• front lathed

What is the main advantage of lathe cutting and polishing soft lenses?

It can make any design, so it is useful for custom orders.

What are the main disadvantages of lathe cutting and polishing soft lenses?

• Higher cost

• Less reproducible (though CAD/CAM helps)

• Lower volume than molding

• Usually lower Dk (silicone is hard to lathe)

• Typically less frequent replacement

How are lathe-cut hydrogel lenses manufactured?

• A button is lathed and polished, similar to GP lens manufacturing

• The lens is then hydrated and autoclaved

What happens to HEMA during hydration in lathe-cut hydrogel lenses, and why is this important?

• HEMA expands ~12% on hydration

• Swelling may not be isometric

• As a result, lens shape may vary with power and become somewhat aspheric

What are the two types of molding used in hydrogel contact lens manufacturing?

• Cast molding

• Injection molding

How are hydrogel lenses typically made with molds?

• Usually the entire lens is molded at once

• Alternatively, one surface (front or back) is molded, and the opposite surface is lathe cut and polished

In contact lens mold manufacturing, what do the male and female tools form?

• Male tool molds the posterior (back) surface of the lens

• Female tool molds the anterior (front) surface of the lens

What materials can be used to make contact lens molding tools?

Tools may be:

• disposable → usually plastic

• reusable → usually steel or quartz

What are the main advantages of molding contact lenses?

• High volume production

• Low cost per lens (after the initial large investment)

• Highly reproducible

What are the main disadvantages of molding contact lenses?

• Limited parameters/design flexibility

• High startup cost to begin production

How does cast molding compare with lathing and injection molding in production volume?

• Higher volume than lathing

• Lower volume than injection molding

How is a lens formed during cast molding?

• A liquid polymer is measured into a cavity

• A limited number of male tools determine the back surface shape

• Female tools are placed on top to form the front surface shape

What happens after the polymer is placed in the mold during cast molding?

• Polymer is cured (e.g., with UV, heat, platinum, etc.)

• Lenses are then released from the molds

What finishing steps may occur after cast molding?

After release from the mold, lenses may be:

• edged, if needed

• hydrated

• surface treated, depending on the polymer type

What are the basic steps of cast molding for soft contact lenses?

• Liquid monomer/polymer is placed into a concave mold

• A convex section/female tool is applied

• The polymer is cured (e.g., UV/heat)

• The finished lens is removed from the mold

What are the main features of injection molding in contact lens manufacturing?

• Used in systems such as J&J “stabilized soft molding” and Alcon “Lightstream technology”

• Process is fully automated

• Requires very high startup cost (well over $500 million)

• But cost per lens is < $1

How is a lens made during injection molding?

• Many male and female tools are assembled in plates with precise cavities

• Polymer is injected between the tools and then cured

What happens to the lens after injection molding?

After molding, the lens is:

• released into the package

• hydrated

• inspected

• labeled

• autoclaved for sterility

How do cast molding and injection molding compare in soft lens manufacturing?

• Cast molding: lower volume than injection molding, liquid polymer placed in mold then cured

• Injection molding: fully automated, highest-volume, very high startup cost, but very low cost per lens

What materials may be used for reusable molding tools in soft contact lens manufacturing?

Reusable molds may be made of:

• quartz

• glass
  Example: used in production of nelfilcon A lenses.

How is quality control (QC) performed in modern high-volume hydrogel lens manufacturing?

QC is largely automated using:

• SPC (statistical process control)

• video imaging robots
  with minimal human involvement.

What additional quality control/regulatory checks are important in hydrogel contact lens manufacturing?

• The polymer itself undergoes substantial QC for:

  • purity

  • physical properties

• The FDA inspects manufacturing plants and requires reporting at least annually.

What are the three main strategies used to manufacture silicone contact lenses with adequate surface wettability?

• Molded, then surface treated with plasma

• Molded with a wetting agent incorporated during curing

• Molded in a multi-step process to create a permanent water surface