Contact Lens-

Manufacturing

Greeshma . G

For Ease Of Manufacturing

The contact lens material should be,

Be homogeneous

Have consistent mechanical properties

Be stress-free and dimensionally stable

Be durable and resist local heating

Be easy to polish

Have predictable hydration characteristics

Lens Materials

Rigid Gas Permeable Lenses

Cellulose Acetate Butyrate

Siloxane Acrylates

t-Butyl Styrene

Fluro siloxane acrylates

perfluroethers

Soft Lenses

• PHEMA (polyhydroxyethyl

methacrylate)

• PVP (polyvinyl pyrrolidone)

• MA (methacrylic acid)

• MMA (methyl methacrylate)

• GMA (glyceryl methacrylate)

• DAA (diacetone acrylamide)

• PVA (polyvinyl alcohol)

Methods of manufacturing

Cast Molding

Lathing

Spin Casting

Reverse Process III (RP III)

Lathing

Advantages

• Established technology

• Simple

• Wide range of parameters

• Suits most materials

• Relatively economic to start production

Disadvantages

• Complex designs difficult

• Labor intensive

• High cost per lens

• Variable surface finish

• Relatively slow

• Volume production difficult

Cast molding

Monomers are mixed and poured into a mold

Tightly controlled temperatures

Lens material is heated or cured to produce a mobile phase

Liquid monomer is injected into

front mold ( ‘female mold’)

Back mold is clamped (‘male

mold’)

UV light- polymerization

Molding

Advantages

• Low cost per lens

• Rapid

• Volume production easy

• Good surface quality

• Good reproducibility

• Complex designs possible

Disadvantages

• Expensive to start production

• Expense limits parameter range

• Not all materials suitable

• Essentially for stock lenses only

Spin-casting

Developed by Otto Wichterle

Concave mold- monomer

solution, cross linking agent and initiator

An open backed mold is spun as a small centrifuge

Shaping of the lens during spinning

Mold defines the front surface of the lens

Rotational velocity, surface tension and gravity combine to

define the back surface.

Lens obtained in swollen state

Advantages

Accurate reproducibility

Precision molds

Controlled spin speed

Generates free formed fluid surface

Consistent, homogenous and thoroughly cross-linked polymer

Surface and interstitial imperfections are least

Reverse process III

Combination of Spin cast & Lathe cut

Spin-casting the front surface and body

Lathing the back surface

Eg : Otima 38 , Soft lens 38

Molding/Lathing combination

Molding the back surface and body of the lens

Lathing the front surface.

Quality Assurance

Preliminary lens assessment – dry state and wet

state

BOZR

BVP

Optical quality

Centre thickness

Edge integrity

Overall quality

Bifocals

Lathing

Molding – single or double-sided or

spin-casting

Spin-casting or lathing combination

Molding or lathing combination