Cl lens manafacturing

Question 1

SCL manafacturing processes

Answer 1

lathe cutting
spin casting
injection moulding
defects

Question 2

RGP manafacturing processes

Answer 2

lathe cutting
cast moulding

Question 3

SCL lathe cutting

Answer 3

An anhydrous “button” of lens material (xerogel) is lathed in a controlled
atmosphere.
The button is mounted on a spinning shaft and shaped with computer-controlled
precision cutting tools.
After the front and back surfaces are shaped with the cutting tool, the lens is then
removed from the lathe and hydrated to soften it.
Sealed in normal saline
Autoclaved at 121 ˚C for 15 minutes

Question 4

lathe cutting terms

Answer 4

Anhydrous – without water
Xerogel – a hydrogel that has not been hydrated [etymology = xero- (“dry”)
gel]
Autoclave – A pressure chamber that is used to sterilize items. Items placed
inside the autoclave are exposed to high temperature steam

Question 5

lathe cutting advatages

Answer 5

Established technology
* Easily adapted for CL manufacturing
* Few limitations on the parameters that can be lathed i.e. virtually any
radius or power can be made
* Reserved for the manufacture of custom or extreme range lenses that
are not amenable to mass production
* Suitable for most materials
* A lathe is a finite investment

Question 6

Lathe cutting disadvantages

Answer 6

More steps and more time consuming than moulding
* Takes a few minutes to make one lens
* Higher unit cost
* Requires strict humidity control
* Cleaning / polishing required on completion
* Variable surface finish
* Lenses must be soaked to remove impurities (unpolymerized monomers) prior to
sterilization and packaging

Question 7

SCL spin casting

Answer 7

Liquid contact lens monomers are poured into mould
Mould is spun in a controlled environment
Rotational velocity, surface tension and gravity defines back curvature
and therefore BVP
Mould shape defines front surface
UV light applied to polymerize the monomers
Edges then buffed and polished
Lenses are then hydrated

Question 8

SCL spin casting advantages

Answer 8

Produces a very smooth (back) surface
Back aspheric surface matches aspheric profile of the cornea
Least likely to produce surface defects

Question 9

SCL spin casting disadvantages

Answer 9

Slower and more complex process than moulding (more steps)
Therefore more expensive
Not as scalable as moulding
Requires edge polishing

Question 10

SCL injection moulding

Answer 10

The soft contact lens monomers is in liquid form
Is injected into computer-designed moulds under pressure
UV light or heat is applied to initiate polymerization. Then
lenses are removed from the moulds
The lenses are then hydrated to soften them
Lenses are verified, packaged and sterilised in the same
way as the spin cast lenses

Question 11

SCL injection moulding advantages

Answer 11

Very quick
Low cost per lens
Easy to produce many lenses at
once
No polishing required
Most widely used method

Question 12

SCl injection moulding disadvantages

Answer 12

Strict environmental control of temperature and humidity
Expensive equipment, huge investment required to setup
Number of moulds limits parameters i.e. good for stock lenses

Question 13

SCL manufacuring final steps

Answer 13

Applicable to soft lenses
1. 3. 4. Anhydrous lens inspected (10x mag)
2. Lens hydrated in saline
Hydrated lens inspected (10x mag)
Lens inserted into blister pack (glass vial for
lathe cut lenses)
5. 6. Blister pack sealed and labelled
Blister pack and lens autoclaved
7. Lenses dispatched