Week 3 - Manufacturing Lenses and Fitting Guidelines

Question 1

What is the base curve (BC) on a contact lens also know as?

Answer 1

central posterior curve

Question 2

What is the optic zone/ posterior zone also known as? 2

Answer 2

-central zone
-apical zone

Question 3

What is the posterior apical radius of the contact lens?

Answer 3

radius of curvature of the back surface of a lens at the apex

Question 4

What does central thickness refer to in a contact lens?

Answer 4

distance between anterior and posterior of the lens at its centre (+ thicker/ - thinner)

Question 5

What is the back vertex power used for?

Answer 5

to measure the power of lenses (back vertex power to focal point)

Question 6

What are the 3 main methods of manufacturing contact lenses?

Answer 6

1. Lathe cutting with manual or
   automated lathes
2. Molding methods
3. Spin casting(injection molding)

Question 7

Which method is faster and more cost-effective? Lathe cutting or injection molding (spin casting).

Answer 7

injection molding process

Question 8

Explain roughly how contact lenses are made during the lathe cut process.

Answer 8

1) A button is used (12 to 15mm)
2) Diameter, base curve, periphery curve are all carved into the button
3) Polished (still a semi finished blank)
4) Anterior surface is cut using lathe
5) Lens hydrated
6) Quality Check
* Surface defects
* Base curve
* Power

Question 9

What are 2 advantages of fitting lathe cut lenses?

Answer 9

• thickness = easier to handle (good for new wearers or px with bad dexterity)
• good centration (stable on eye, consistent vision correction)

Question 10

What are 3 disadvantages of fitting lathe cut lenses?

Answer 10

-Time consuming
-Expensive (custom)
-Hard to reproduce

Question 11

Lathe cutting allows for highly customisable lenses great for High Rx, RGPS, keratoconas cornea etc. T/F

Answer 11

TRUE

Question 12

Explain roughly how to cast molding contact lenses.

Answer 12

1. Lens is pressed into place
2. Anterior mold is injected with liquid monomer
3. Posterior mold used to close on top
4. Mold taken through series of UV lights –
   eventually lens hardens
5. Finished lens produced (good optics and smooth surfaces

Question 13

Cast molding is good for mass productions. T/F

Answer 13

TRUE

Question 14

What are the most common ways to make contact lenses now? 2

Answer 14

lathe cutting
Molding methods

Question 15

Explain roughly the spin casting (injection mold) method of using contact lenses.

Answer 15

1) Liquid polymer is injected into the spinning mold
2) Spins lenses into shape
3) Aspheric base curve is formed by the spinning force
4) UV light is applied to solidify or cure the lens
5) Periphery of lens is buffed and polished
6) Lens then is hydrated

Question 16

What process is usually done to create RGP lenses?

Answer 16

Lathe cut lenses

Question 17

Avoid polishing compounds with water in when polishing contact lenses. T/F

Answer 17

TRUE

Question 18

What are 3 advantages of cast molding?

Answer 18

-precision
-consistency
-efficient method

Question 19

What is the most commonly used process for making soft contact lenses?

Answer 19

Cast molding

Question 20

What are 5 advantages to spin casting (injection mold)?

Answer 20

• Smooth surfaces
  -Enhanced comfort during wear
  -Back aspherical surface matches with the aspheric profile of
  the cornea
  -Minimal lens movement on the eye with acceptable tear
  film
  -One base curve makes it easy to fit

Question 21

Spin cast lenses are easy to replicate. T/F

Answer 21

True

Question 22

Which process starts out as a rod or a button of material?

Answer 22

Lathe cutting

Question 23

What should we consider when determining a px will be good candidate for soft cls? 6

Answer 23

• lifestyle
  -motivation
  -physical state - dexterity
  -eye conditions
  -willingness to comply
  -General environment of wear - lens hydration

Question 24

What is part of the pre-fitting examination? 3

Answer 24

-assesing if they are good candidates
- ocular measurements for inital fit
-collect baseline clinical information to compare with later

Question 25

Review the questions to ask during history taking (pre-fitting soft lenses). Turn over card.

Answer 25

* Have you ever worn contact lenses in the past? * If yes, how many years have you worn contact lenses? * If yes, what is the brand of lenses you are currently using? * If yes, have you used other brands? * If yes, when? Why did you switch? * If yes, what time do you insert your lenses and what time do you remove them? * If yes, how many times a week do you wear your lenses? * If yes, how old are the lenses you are currently wearing? * Are your lenses comfortable from the time you wear them to the end of the day? * How do you clean your lenses? * What solution do you use? * Are you able to wear the contact lenses comfortably all day? * How is your vision when wearing the lenses? * Not all questions are listed based on patient answers will determine the direction of you next set of questioning.

Question 26

What do we do if a patient arrives wearing contact lenses to their contact lens fit in regards to the Visual Acuity? 3 steps

Answer 26

1. Assess VA with contact lenses on 2. Next assess CL under slit lamp 3. Then have the Px remove lens and do unaided VA

Question 27

What do we do if a patient arrives not wearing contact lenses to their contact lens fit in regards to the Visual Acuity? 2 steps

Answer 27

1. Assess unaided VA's 2. Next assess VA's with eyeglasses worn

Question 28

What are the 7 other physical measurements and checks we can do before fitting contact lenses?

Answer 28

-HVID -PA / PF -K’ readings -Lid eversion -Tear Break up -Tear Prism -get eyeglass prescription

Question 29

Do not test unaided VAs on someone who is +/-4.00D as it is unnecessary information (can not see anything) T/F

Answer 29

TRUE