CL Manufacturing Flashcards
SCL methods
- lathe cutting
- spin casting
- cast mould
Combination methods
- moulding + lathing
- spin casting + lathing
What is lathe cutting
- Anhydrous button is lathed in a controlled atmosphere
- button mounted on a spinning shaft, and shaped with a computer cutting tool
- lens is then removed and hydrated to soften it, and then sealed in saline
- autoclaved at 121 degrees for 15 mins
Lathe cutting advantages
- few limitations of Rx
- established for CL manufacturing
- easily adapted for CL manufacturing
- reserved for customer extreme ranges
- suitable for most materials
Lathe cutting disadvantages
- increased cost
- time consuming
- variable surface finish
- strict humidity control
- cleaning/polishing required
- lenses must be soaked
What is spin casting
- liquid monomers poured into mould
- mould is spun in controlled environment
- rotation velocity/surface tension/gravity defines the back curvature (BVP)
- mould shape defines front surface
- UV light applied to polymerase monomers
- edges then buffed and polished
- lens hydrated
Spin casting advantages
- very smooth back surface
- back surface matches corneal profile
- least likely to produce surface defects
Spin casting disadvantages
- slower and more complex
- more expensive
- not as scalable as moulding
- requires polishing
What is injection moulding (cast mould)
- monomers injected into cast a high pressure
- UV light or heat initiates polymerisation, then lenses removed
- lenses are then hydrated to soften
- lenses are verified, packaged and sterilised in same way as spin casting
Injection moulding advantages
- very quick
- low costs
- easy to produce
- many lenses at once
- most widely used
Injection moulding disadvantages
- strict environmental control
- expensive equipment
- number of moulds limits parameters
RGP manufacturing
- lathe cutting
- cast moulding
RGP lathe cutting
- similar to SCL
- reduced margin of error
- separately configured lathes for front and back surface
- engraving/marking is common on RGP lenses stored dry
RGP cast moulding
- Similar to soft lens material
- lens left to dry
- mould broken apart and lens revealed
Toric manufacturing
- dual axis lathing on stationary lens
- can produce any shape
- blank lens is crimpled across the front surface, then worked into a sphere, releasing the crimpling leaving a toric surface
- moulding requires a separate mould for each Rx
- dual axis flying cutter, the cutter set to particular axis as this passes by the rotating lens button it creates the toric shape
Toric manufacturing - stabilisation methods
Prism ballast
- 1 or 1.5 base down prism traditionally
- balances the thickness profile to minimise rotational effects
- RGP and SCLs
- produced by software
Dynamic stabilisation
- dual thin zones or double slab off top and bottom portions of the lens
- truncation rarely used
- removing 1/1.5mm chord from the lower eye
- excellent stabilising but can be uncomfortable
Multi focal manufacturing
Segmented design
- 2/3 portions make up an alternating lens, can be fused or solid portions with a range of segmented shapes
- stabilised with prism or truncation
- more commonly RGP
Simultaneous vision
- concentric rings of diffractive pattern are moulded onto lens back surface
Hybrid CL
- similar process to lathe cut soft contact lenses
- plastic discs cut with the lathe have a rigid centre, surrounded by non-hydrated SCL material
- the 2 materials are bonded together with prepriatary techniques to prevent separation of materials
Scleral CL
- lathe cutting
- production as for CL, plus cutting of scleral portion
- take mould of the eye and scleral topography to measure shape
Types of tints
- handling tint
- therapeutic tint
- cosmetic
- dyslexia
- prosthetic
- sport
- theatric
Types of translucent tints
- dye dispersion
- vat dye testing
- chemical bonding tint
- printing
Types of opaque tints
- dot matrix tint
- laminate
Quality assurance in RGPs
- inspection with 10x mag
- power
- BOZR
- TD
- optic zone diameter
- lens thickness
- cleaned and dispatched
Quality assurance of SCLs
- inspected dry
- hydrated
- inspected wet
- packaged
- autoclaved
- dispatched
