CL manufacturing Flashcards
SCL methods
- lathe cutting
- spin casting
- cast mould
Combination methods
- moulding + lathing
- spin casting + lathing
Lathe cutting
- Anhydrous button lathed in controlled atmosphere
- button mounted on a spinning shaft & shaped with a computer cutting tool
- lens then removed & hydrated to soften it & sealed in saline
- autoclaved at 121 degrees for 15 mins
Lathe cutting Advantages + Disadvantages
ADVANTAGES
- few limitations on Rx
- established for CL manufacturing
- reserved for customer extreme ranges
- suitable for most materials
DISADVANTAGES
- increased cost
- time consuming
- variable surface finish
- strict humidity control
- cleaning/polishing required
- lenses must be soaked
Spin casting
- liquid monomers poured into mould
- mould 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 + polished
- lens hydrated
Spin casting Advantages + Disadvantages
ADVANTAGES
- very smooth back surface
- back surface matches corneal profile
-least likely to produce surface defects
DISADVANTAGES
- slower + more complex
- more expensive
- not as scalable as moulding
- requires polishing
Injection moulding (cast moulding)
- monomers injected into cast at high pressure
- UV light / heat initiates polymerisation, then lenses removed
- lenses then hydrated to soften
- lenses verified, packaged + sterilised in same way as spin castin
Injection moulding Advantages + Disadvantages
ADVANTAGES
- very quick
- low cost
- easy to produce
- many lenses at once
- most widely used
DISADVANTAGES
- strict environmental control
- expensive equipment
- No. of moulds limits parameters
RGP manufacturing
Lathe Cutting
- similar to SCL
- reduced margin of error
- separately configured lathes for front & back surface
- engraving/marking is common on RGP lenses stored dry
Cast Moulding
- similar to SCL
- lens left to dry
- mould broken apart & lens revealed
Toric manufacturing
- dual axis lathing on stationery lens
- can produce any shape
- blank lens is crimpled across front surface, then worked into a sphere, releasing the crimpling leaving a topic 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 topic shape
Toric manufacturing - stabilisation methods
PRISM BALLAST
- 1/1.5 base down prism traditionally
- balances thickness profile to minimise rotational effects
- RGP & SCLs
produced by software
DYNAMIC STABILISATION
- dual thin zones / double slab off top & bottom portions of the lens
- truncation rarely used
- removing 1/1.5mm chord from lower eye
- excellent stabilising but can be uncomfortable
M/F manufacturing
SEGMENTED DESIGN
-2/3 portions make up an alternating lens, can be fused / solid portions with a range of segmented shapes
- stabilised with prism / truncation
- more commonly RGP
SIMULTANEOUS VISION
- concentric rings of diffractive pattern are moulded onto lens back surface
HYBRID CL
- similar process to lathe cut SCL
- plastic discs cut with lathe have 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 eye & 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
- don’t matrix tint
- laminate
Quality assurance of SCL
- inspect dry
- hydrated
- inspect wet
- packaged
- autoclaved
- dispatched
