Manufacturing of CLs

what are the different ways SCL are made

lathe cutting

spin casting

cast modulating

combination

describe lathe cutting

fast rotating tool cuts into required shape

polished

hydrate to form finished lens with saline

seal in sterile vials

what does the back surface curvature decide in lathe cutting

shape

what does the front surface curvature decide in lathe cutting

power

advantages of lathe cutting

any rx / curvature

thicker lenses so easier to handle

good movement and centration

disadvantages of lathe cutting

labour intensive

expensive

hard to reproduce

describe spin casting

stainless steel tool creates PVC moulds

little polishing needed

liquid monomers injected into a mould

spinning forms aspheric base curve of CL

what is applied to the material to solidify it in spin casting

UV light

what is lens geometry determined by in spin casting

spin speed and volume of monomers

what is lens power determined by in spin casting

spin speed

what is centre thickness determined by in spin casting

amount of monomer injection

advantages of spin casting

smooth edge profile and overall surface

enhanced comfort during lens wear

back aspheric lens design matches well with aspheric cornea

easy to fit

examples of manufacturing defects on the edges

nick - small piece missing

tear

roughness

excess material

examples of manufacturing defects on the body

split

blemish - hazy regions

multiple pieces