This document summarizes various contact lens manufacturing techniques. It discusses soft lens manufacturing methods like moulding, spin casting, and lathing. It describes how these techniques work, their advantages and disadvantages. Rigid gas permeable contact lenses are lathed from cylindrical buttons using back surface and front surface lathes. Additional processes for both soft and rigid lenses include edge polishing, marking, fenestration and final inspection. The document is intended as an overview of contact lens manufacturing processes.
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• Surface Preparation
• Coating (Spin Casting)
• Pre-Bake (Soft Bake)
• Alignment
• Exposure
• Development
• Post-Bake (Hard Bake)
• Processing Using the Photoresist as a Masking Film
• Stripping
• Post Processing Cleaning (Ashing)
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2. Introduction
Medical devices that rests against the highly sensitive eyeball
Contact lens needs to be of the highest quality in terms of their
physical construction
Devices that correct optical defocus, the optical quality of contact
lenses must be higher
2
4. Starts with an anhydrous button
Strict control of environment factors especially humidity
Numerical control increases both the complexity of the design and level
of production
Diamond tipped tool
Cleaning and hydration
Sealed in normal saline
Packed product and the autoclaved (120 degree for at least 20 minutes)
Lathing
4
6. Advantages Disadvantages
Well established technology Labour intensive
Wide range of parameters High cost per lens
Suits most materials Variable surface finish
Starts depend on capital
budget
Volume production difficult
Lathing
Image courtesy: Nathan Efron and Steve Newman, Second edition Contact lens practice
6
A laboratory using the labour-intensive method of lathe cutting
to manufacture soft contact lenses
7. Raw materials are liquid monomers
Male and female mould
Monomer’s introduced into spinning mould
Centrifugal force and gravity defines the back surface and BOZR
Mould defines the front surface
Front surface finish depends on mould finish
Back surface depends on surface tension and other properties
of the resulting polymer
Spin casting
7
9. Advantages
Accurate reproducibility
Precision moulds
Controlled spin speed
Generates free form fluid surface
Surface and interstitial imperfections are least
Disadvantages
Edge thickness
Image courtesy: Nathan Efron and Steve Newman, Second edition Contact lens practice
9
A manufacturing line for spin casting soft contact lenses.
10. Dominant technology in high volume lens manufacture
Matching male and female moulds
Monomer in liquid form- introduced into a concave female
mould-front surface
Ultraviolet transparent male mould clamped with the female
mould in controlled environment
Polymerisation-UV light
Cast moulding
10
12. Advantages Disadvantages
Low cost Expensive to start production
Volume production Expense limits and parameter
range
Good surface quality and
reproducibility
Not all materials suitable
Complex designs possible Stock lenses
Cast moulding
Image courtesy: Nathan Efron and Steve Newman, Second edition Contact lens practice
12
Generating a metal master tool
A manufacturing laboratory for cast moulding soft
contact lenses.
13. Reverse Process III
Combinations of spin cast and lathe cut
Spin casting the front surface and body
Lathing the back surface to define BOZR and design
OR
Spin casting the body and back surface
Lathing the front surface to give BVP and design
13
15. Stabilized soft moulding
Inert water substitute is mixed with lens monomers before
polymerisation
Water replaces the substitute at hydration
Significantly less expansion on hydration
Better optical quality and surface finish
Quicker hydration
15
16. Rigid lens manufacturing
Raw materials
Flat cylindrical buttons of 12.7 mm diameter and 4.3 mm
circumference thickness
Supplied in various colours and the trade name imprinted
on one surface of the button
Super gas-permeable with Dk values over 150
Used the latest rigid gas permeable materials
Image courtesy: Nathan Efron and Steve Newman, Second edition Contact lens practice 16
Rigid lens buttons
17. Generating the lens back surface
Button is first secured in a carrier or dolly
Button clamped to a back surface lathe
Set spinning at high rate about its central axis
Diamond tipped tool
To obtain smooth and high quality finish
To the required size of the finished lens
Button released from the lathe and given a brief polish
17
18. Image courtesy: Nathan Efron and Steve Newman, Second edition Contact lens practice
18
Back surface lathe
Button about to be mounted in dolly.
Button–dolly assembly is
collected in lathe
19. Image courtesy: Nathan Efron and Steve Newman, Second edition Contact lens practice
19
Back surface curve being cut into the button with a
diamond-tipped tool
Back surface polishing.
20. Generating the lens front surface
The button needs to be fixed on to mount, or arbour – Blocking
The arbour can be metal or plastic cylindrical tool,
one end dome shaped
Heats the arbour approx. 800 C and applies low melting point wax
to dome end, or in case of plastic tool, applies UV sensitive which can
be cure to hard form
Arbour button clamped into a front surface lathe
Centration under magnification
Cut is made from the edge to the centre with diamond-tipped cutter,
then with fine diamond tipped cutter
Button is released from the lathe and mounted to polishing machine
(30 secs to 2 mins)
20
21. Image courtesy: Nathan Efron and Steve Newman, Second edition Contact lens practice
21
Blocking the button on to a brass arbour Front surface lathe
Front surface curve being cut into the button
with a diamond-tipped knife.
Front surface polishing.
22. Engraving, marking and fenestration
Near finished lens still mounted on arbour
Engraving-pantographic device
Engrave on the lens against a stainless steel master template
Typical engraves since R and L, then BC and total diameter
Fenestrations can be introduced into the lens using a laser (done
in finished lens)
Image courtesy: Nathan Efron and Steve Newman, Second edition Contact lens practice 22
Near-finished lens form wax-mounted
on the brass arbour
Pantographic system for lens engraving
Laser system for toric lens scribe marking and
Introducing fenestrations.
23. Edge polishing and final inspection
Edge polishing can be done by using a polishing machine
The lens surface on to a concave rubber cap support
The spindle rotates around the long axis and lowered on to a flat rotating
polishing pad and moved slowly from side to side
After polishing, the edges are inspected using a 10X hand magnifier
Any irregularities can be rectified manually by polishing the lens
Image courtesy: Nathan Efron and Steve Newman, Second edition Contact lens practice 23
Two lenses suction mounted to the spindles of an
edge-polishing machine, ready to be lowered on to
rotating pads.
Inspecting the lens edges using a 10× hand
magnifier Manual polishing of the lens edge.
Molding - xerogel.
Monomers are mixed and then poured into a
mold (single or double sided) in the absence of
water/water vapour (and usually air/oxygen as
well) at tightly controlled temperatures.
• Spin-casting.
An open-backed mold is spun as a small
centrifuge. The mold defines the front surface
of the lens. Rotational velocity, surface tension
and gravity combine to define the back surface.
• Lathing - xerogel.
An anhydrous button of lens material is lathed
conventionally in a controlled atmosphere.
Manufacturers are researching methods of
eliminating the need for surface polishing by the
application of high-precision engineering
principles and other advances such as air
bearings and anti-vibration mounts.
• Molding/Lathing combination.
Usually a combination of molding the back
surface and body of the lens and lathing the
front surface.
• Spin-casting/Lathing combination.
Usually spin-casting the front surface and body
of the lens and lathing the back surface.
• Molding - Stabilized Soft.
In this recent innovation, a space-taking inert
diluent is included in the mix of monomers
during molding/polymerization. The diluent is
replaced by water at a later stage. The final
product is quick to hydrate fully, undergoes
minimal expansion on final hydration and
provides high quality optics and surface finish.
The process of manufacturing a soft contact lens by lathe cutting. (1) The dry polymer is supplied as a rod or button. (2) A polymer button is
placed on a lathe; the button spins and a diamond tool is advanced towards the button to generate the lens back surface. (3) The button is released from the
back surface lathe. (4) The button is mounted on a front surface lathe with adhesive wax; the button spins and a diamond tool is advanced towards
the button to generate the lens front surface. (5) The dry lens is removed from the lathe and the edges are polished. (6) The lens is inspected at 17×
magnification. (7) The dry lens is placed in saline to hydrate the lens, which swells to its final soft lens form. (8) The hydrated soft lens is inspected at 10×
magnification. (9) The soft lens is inserted into a glass vial containing saline. (10) The glass vial is sealed and labelled. (11) The sealed glass vial containing the
lens is sterilized in an autoclave. (12) The individual glass vials are despatched.
Change to 7 the slide
Auto calve 120 0 C for 15 to 20 minutes
Once the blister pack is opened, what will happened to the content in blister solution?
What will be the base curve value for selecting the mould based on the power?
The process of manufacturing a soft contact lens by spin casting. (1) A male tool is machined from stainless steel; the contour of the tool head
will define the shape of the anterior lens surface. The same tool is used to make hundreds of thousands of moulds. (2) A female mould is made by pressing
the male tool into molten polypropylene, which cools and sets. (3) The female mould is mounted, with the concavity facing upwards, in a spindle that spins
about the lens axis, and liquid monomers are introduced into the spinning mould. (4) The monomers in the spinning mould are irradiated with ultraviolet
light to initiate lens polymerization. (5) The dry lens is removed from the mould, the lens edge may be polished and the mould is discarded. (6) The edge of
the dry lens is inspected at 10× magnification. (7) The dry lens is placed in saline, which hydrates the lens, causing it to swell to its final soft lens form. (8) The
hydrated soft lens is inspected at 10× magnification. (9) The soft lens is inserted into a blister pack containing saline. (10) The blister pack is sealed with a
special foil, and a label is stuck on to this. (11) The sealed blister pack containing the lens is sterilized in an autoclave. (12) The individual blister packs are
inserted into packages, typically in multiples of either three or six lenses.
Is the minus lens is a disadvantage for edge thickness in spin casting ??
The process of manufacturing a soft contact lens by cast moulding. (1) Male and female tools are machined from stainless steel; the contour of
the male tool head will define the shape of the anterior lens surface, and the contour of the female tool head will define the shape of the posterior lens
surface. The same tools are used to make hundreds of thousands of moulds. (2) Male and female moulds are made by pressing the tools into molten
polypropylene, which cools and sets. (3) The female mould is mounted in an accurate aligning fixture, with the concavity facing upwards, and liquid
monomers are introduced into the concavity. (4) The male mould is registered over the female mould and the two moulds are clipped together. (5) Excess
polymer is squeezed out from the sides of the mould. (6) The monomers inside the mould assembly are irradiated with ultraviolet light or thermal energy to
initiate lens polymerization. (7) The dry lens is removed from the mould and the moulds are discarded. The final stages of lens production are essentially the
same as for spin casting, which is illustrated in steps 6–12
The master tools
are used to make hundreds of thousands of male and
female moulds.