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Contact Lenses - Year 2 > Manufacturing Contact Lenses > Flashcards

Manufacturing Contact Lenses Flashcards

1
Q

What are the different ways of manufacturing SCLs?

A

-Lathe cutting

  • Spin casting
  • Cast moulding
  • Combination of spin or cast with lathe
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2
Q

How is lathe cutting used to produce a SCL ?

A

A Special CL lathe (a fast rotating tool) is used to cut a hard button (of material zero gel) into the required shape, which is polished carefully, then hydrated to form the finished soft lens which is placed in a vial then autoclave before being ready to be sold.

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3
Q

In lathe cutting what does the back surface curvature determine?

A

Back surface curvature decides the shape.

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4
Q

In lathe cutting what does front surface curvature decide?

A

Front surface curvature decides the power

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5
Q

Is manufacture of SCLs via the lathe cutting method expensive?

A

Yes (as a pose to spin casting or cast molding), even if you automate the system due to the sheer number of steps this method is expensive.

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6
Q

What quality control checks would take place in lathe cutting?

A

Checks for surface defects

That the base curve is correct

That the Back Veretx Power (BVP) is correct.

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7
Q

In lathe cut manufacturing for SCLs what happens after the lens has been cut, hydrated and quality checked?

A

The lens is sealed in a sterile vial and place in an autoclave at 120 degrees for 15-20 minutes.

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8
Q

Generally what do we reserve lathe cutting for?

A

Custom order or extreme range lenses that aren’t necessarily widely commercial such as lenses of high sph or toric powers.

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9
Q

What are the advantages and disadvantages of lathe cutting as a means of manufacure?

A
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10
Q

What happens in spin casting as a manufacture technique?

A
  • ‘Male’ stainless steel tool to create ‘female’ PVC moulds
  • Liquid monomers are injected into mould
  • Centripetal force from spinning forms aspheric base curve of CL

– Front curve formed by curvature of male mould

– UV light is applied to solidify the material

[Basically need to know the photo]

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11
Q

In spin casting what is lens geometry determined by?

A

Lens geometry is determined by spin speed and volume of monomers

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12
Q

In spin casting what is lens power determined by?

A

Spin speed

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13
Q

In spin casting what is centre thickness of the lens dependant on?

A

Centre thickness of the lens is dependent on the amount of monomer injection

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14
Q

What are the advantages of Spin casting?

A
  • Smooth edge profile and overall surface this means enhanced comfort during lens wear
  • Back aspheric lens design matches well with aspheric cornea which results in minimal lens movement with acceptable tear film dynamics
  • Easy to fit these lenses

[This method requires minimum polishing of lens needed]

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15
Q

How are CLs made from cast molding?

A
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16
Q

What is the dominant method of manufacture for SCLs?

A

Cast moulding.

17
Q

Does cast moulding typically take place via batch production or continuous production?

A

Normally continuous production

18
Q

What is curing?

A

Where the monomer is exposed to either thermal energy or ultra violet ( basically sets bonds).

19
Q

How are tinted lenses typically made?

A

Cast moulding

20
Q

What are manufacturing defects that need to be checked for in the production of contact lenses ?

A

Edge defects:

  • Nick: small piece missing from edge
  • Tear: partial or full separation on material incl edge
  • Roughness: uneven edge profile
  • Excess material or flash: surplus material

Body defects:

  • Split
  • Blemish: hazy/ low transparent region, on or within lens
  • Eccentric optic zone: Optic Zone not concentric with lens perimeter (i.e. not centered)
  • Multiple pieces (as in it got split into multiple pieces)
21
Q

Is CL production/manufacture reglated?

A

Yes as they are deemed a medical device thus heavily regulated including how they are stored.

22
Q

What are the methods for manufacturing RGP lenses?

A

Only lathe cutting.

23
Q

Can RGP lenses be marked or engraved?

A

Yes

24
Q

What does BVP stand for?

A

Back vertex power

25
Q

What is the back optic zone?

A

It is the area of the contact lens, through which the px has optically the best vision.

26
Q

Does significant centre thickness affect the weight of the lens?

A

Yes- imagine how much thicker (at the centre) and heavier a +20.00D lens would be compared to a +2.00D lens.

[This could cause the lens to drop]

27
Q

What does the concept of edge lift refer to?

A

The edge of the CL not making contact with the cornea

28
Q

In RGP lenses do you want a big edge lift or a small edge lift ( i.e. do you want a big distance between the cornea and the lens or a small distance)?

[Refer to the two CLs in the picture]

A

You wat a big edge lift. You don’t want the edge of the CL to touch the cornea as the tears that are sitting below the contact lens will have nowhere to go (Tear exchange).

[Good Tear exchange is really important in an RGP Fitting].

29
Q

What is tear exchange and why is it important?

A

Tear exchnage means that with every blink the tears behind the CL are being replaced with fresh ones thus bacteria don’t have a chance to settle in and start ‘nibbling’ away at the epithelium or even stroma.

30
Q

True or false- even small differences in edge lift can make huge differneces to comfort and stabilisation of the CL?

A

True.

[The more edge lift the better]

31
Q

True or false- edge lift can prevent binding of the CL to the cornea?

A

True - this makes RGPs easier to remove.

32
Q

True or false- RGP lenses can be completely customised - any lens can be made?

A

True

33
Q

How can we predict what the RGP lens will look like and how it will fit?

A

RGPs (as well as SCL) come with a fitting guide.

Software can be used to visualise how the CL will fit the cornea and its dimensions.

Online calculators for RGP lenses are avilable to again check dimensions.

34
Q

Sumarise all the methods for manufacture of SCLs and RGP.

A
35
Q

Why has lathe cutting become the dominant means of manufacture for SCL?

A

It can produce CLs in high volumes with high precision and as a result is apt in dealing with the high demand for CLs

36
Q
A

Contact Lenses - Year 2 (18 decks)

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