Contact Lens
Manufacturing
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SPONSORS
Development and delivery of contact lens education by IACLE is supported
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Published in Australia by
The International Association of Contact Lens Educators
First Edition 1997
©The International Association of Contact Lens Educators 1996
All rights reserved. No part of this publication may be reproduced, stored in a
retrieval system, or transmitted, in any form or by any means, without the prior
permission, in writing, of:
The International Association of Contact Lens Educators
IACLE Secretariat,
PO Box 656
Kensington NSW 1465
Australia
Email: iacle@iacle.org
CONTRIBUTORS
Contact Lens Materials and Manufacturing :
Lewis Williams, AQIT(Optom), MOptom, PhD
For a complete list of acknowledgements please see our website: www.iacle.org
RGP LENSES
MANUFACTURING
ASPECTS
RGP MANUFACTURING
Care with:
•Blocking
•Cutting
•Polishing
•Solvents
RGP MANUFACTURING
Poor wettabilitiy associated with:
•Over-polishing
(Walker, 1989)
•Incorrect use of solvents
(Hogg, 1995)
•Use of incorrect solvents
(Hogg, 1995)
FSAs/SAs
MANUFACTURING DISADVANTAGES
• Softer materials
• Difficult to get highly polished surface
• Materials susceptible to ‘burning’
• Solvents can affect the surface
FSAs/SAs
MANUFACTURING DISADVANTAGES
• Significant flattening of BOZR
• Higher Dk lenses difficult to modify
• Lower reproducibility
FSAs/SAs
MANUFACTURING DISADVANTAGES
• Manufacturing more difficult
• More sophisticated equipment required
• Increased production costs
• Lower yields than PMMA
RGP LENSES
MANUFACTURING
METHODS
RGPs
LENS FABRICATION TECHNIQUES
• Lathing
• Molding
LATHING ADVANTAGES
• Established technology
• Simple
• Wide range of parameters
• Suits most materials
• Relatively economic to start production
LATHING DISADVANTAGES
• Complex designs difficult
• Labour intensive
• High cost per lens
• Variable surface finish
• Relatively slow
• Volume production
difficult
• Reproducibility
MOLDING ADVANTAGES
• Low cost per lens
• Rapid
• Volume production easy
• Good surface quality
• Good reproducibility
• Complex designs possible
MOLDING DISADVANTAGES
• Expensive to start production
• Expense limits parameter range
• Not all materials suitable
• Essentially for stock lenses only
RGP CONTACT LENSES BIFOCALS
Translating
• Concentric (annular), distance centre
• Progressive addition
• Implanted segment
Non-Translating
• Diffractive
• Concentic, distance centre
• Minimal movement is essential, but physiologically
undesirable
MANUFACTURING RGP LENSES
• Concentric and progressive: made using
conventional lathing or molding techniques
• Implanted segments: high refractive index
segment incorporated in button. Usually ‘D’ or
crescent-shaped
• Diffractive: concentric zones molded onto
back surface
TINTED RGP CONTACT LENSES
Either:
• Dye is dissolved in monomer
before mixing and polymerization
or:
• Pigment is dispersed in monomer
before mixing and polymerization
SOFT CONTACT LENS
MANUFACTURING
SOFT LENS MANUFACTURING
METHODS
• Molding - anhydrous (xerogel)
• Spin-casting
• Lathing - xerogel
• Molding/lathing combination
• Spin-casting/lathing combination
• Molding - stabilized soft
SOFT LENS MANUFACTURING
MOLDING
SOFT LENS MANUFACTURING
MOLDING
• Starts with liquid monomers
• Similar to RGP process
• Requires controlled environment,
especially humidity, and often needs to be
O2-free
• Polymerization initiator required (usually
UV)
• Subsequent steps similar to lathed product
SOFT LENS MANUFACTURING
LATHING
• Starts with an anhydrous button
• Method similar to RGPs
• Requires strict control of environment especially of
humidity
• Cleaning and hydration required upon completion
• Lens sealed in normal saline
• Packaged product then autoclaved
(121oC for 15 minutes)
SOFT LENS MANUFACTURING
SPIN-CASTING
SOFT LENS MANUFACTURING
SPIN-CASTING
• Starts with liquid monomers
• Monomers introduced into spinning mold
• Centrifugal force and gravity defines back
surface shape and BOZR
• Mold defines front surface
SOFT LENS MANUFACTURING
SPIN-CASTING/LATHING COMBINATION
• Starts with liquid monomers
• Body and front surface spin-cast
• Back surface lathed to define BOZR
and design
SOFT LENS MANUFACTURING
SPIN-CASTING/LATHING COMBINATION
• Starts with liquid monomers
• Body and back surface spin-cast
• Front surface lathed to give BVP
and design
SOFT LENS MANUFACTURING
STABILIZED SOFT MOLDING
• Developed for volume production
• An inert water substitute is mixed with
lens monomers before polymerization
• Water replaces the substitute at
hydration
SOFT LENS MANUFACTURING
STABILIZED SOFT MOLDING
• Significantly less expansion
on hydration
• Better optical quality
• Better surface finish
• Quicker hydration
• Enhanced reproducibility
SOFT LENS MANUFACTURING
PACKAGING
• Glass vial
-screw or crimp lid
• Poly(ethylene terephthalate) (PET) vial
-screw or crimp lid
• Foil pack (disposables)
• Multi-blister pack (daily disposables)
SOFT LENS MANUFACTURING
AUTOCLAVING
• All products are autoclaved
after manufacture, regardless
of water content
• Foil and blister packs may
require a special autoclave
SOFT LENS MANUFACTURING
ASPHERIC
• Template-following lathe
• ‘Plunge’ tool, full or half diameter
• x,y numerically controlled lathe
• Molding - single/double-sided or
spin-casting
SOFT LENS MANUFACTURING
TORIC
• Toric machining
• Crimped then worked as a sphere
• Dual-axis ‘flying’ cutter (slab-off torics)
• Molding - single/double-sided or
spin-casting
• Combinations of the above
FRONT SURFACE TORIC GENERATOR
(Flying Cutter)
rB = Radius of rotation - lens button
Motor
rC = Radius of travel - traversing cutter
Rotating lens button
Button path
Cutter path rC
rB & rC define the readii
of the principal meridians
Traversing cutter
Traversing cutter axis
SOFT LENS MANUFACTURING
BIFOCALS
• Concentric (annular)
-Distance centre
-Near centre
-Distance centre, progressive near
SOFT LENS MANUFACTURING
BIFOCALS
• Diffractive bifocal
-diffractive optics on back surface
• Translating bifocal
-how much translation possible?
SOFT LENS MANUFACTURING
BIFOCALS
• Lathing
• Molding - single/double-sided or
spin-casting
• Spin-casting/lathing combination
• Molding/lathing combination
THANK YOU
Feedback on errors, omissions, or suggestions for
improvement are invited. Please contact us at:
iacle@iacle.org
See the following slides explaining the symbols,
abbreviations, and acronyms used in the IACLE
Contact Lens Course
CLICK to return
Table of Contents
to the first slide
14
SYMBOLS
ABBREVIATIONS
ACRONYMS
ACRONYMS
