9. How to: Soft lens fitting

Question 1

What are the 6 base-line date required for soft CL fit?

Answer 1

1. H&S
2. Spectacle Rx
3. Keratometry
4. Base line measurements: HVID and VPA
5. Anterior eye examination
6. Tear film assessment

Question 2

What is keratometry used for and what is it not useful for?

Answer 2

Used as a base-line test to know the curvature of the ocular surface.
Not used: to select a specific lens

Question 3

Why is corneal staining check done when patient comes in to CL appointments?

Answer 3

To ensure no damage was done in the application and remove of Contact lenses

Question 4

BC is also known as what sometimes?

Answer 4

BOZR: Back optic zone radius

Question 5

What is BC mean?

Answer 5

Radius of curvature of the back of the lens

Question 6

What is meant by TD?

Answer 6

Total diameter
This is the overall size of the lens

Question 7

Sag is determined by?

Answer 7

BC and TD

Question 8

What happens to sag if TD of a lens is altered?

Answer 8

Sag is altered

Question 9

Sag influences what?

Answer 9

Lens fit

Question 10

When fitting patient with soft CL, what is the aim?

Answer 10

To achieve optimal fit: a comfortable, well- centered lens and provides a stable vision.

Question 11

Why are silicone lens stiffer then hydrogels?

Answer 11

Silicone lenses have a higher modules.

Question 12

How do you decide which BC to fit patients with? - 2 methods

Answer 12

1. If 2 different BC available, fit patients with the 2 different BC and let them decide with one is more comfortable- during initial fitting.
2. Use manufacturers guide to decide which lenses should be used.

Question 13

How is contact lenses recorded into patient records?

Answer 13

Manufacturer & lens name
BC/ TD/ Power

Question 14

Before fitting lenses in patient, what should you check on the package?

Answer 14

Expiry date

Question 15

3 ways of checking that a lens is the right way round?

Answer 15

1. Check the profile
2. Crease test
3. Lens inversion marking

Question 16

Ideally how long do you let lenses settle before checking its fit?

Answer 16

10 minutes

Question 17

What light is used to check soft lens fit vs RGP lenses?

Answer 17

Soft lenses: white light
RGP lenses: Fluorescein

Question 18

9 features used to determine lens fit?

Answer 18

1. Centration
2. Edge alignment
3. Coverage
4. Lag & Sag
5. Movement on blink
6. Push- up test
7. Patient comfort
8. Vision
9. What kind of fit the lens gives

Question 19

Centration of lens is seen with what mag?

Answer 19

Low mag

Question 20

How is centration of a lens determined?

Answer 20

Done in primary position: compare centre of CL to centre of cornea

Question 21

Process of checking centration of a lens?

Answer 21

Beam in SL is aligned to to the width one side, once the beam and overlap are aligned. Move the beam to the opposite side and compare to the reference beam.

Question 22

What is good edge alignment in a lens?

Answer 22

Edge of the lens should align with conjunctival

Question 23

Steep lens fitting causes?

Answer 23

Conjunctival indentation and blanching of vessels

Question 24

Flat fitting lenses may show what when edge alignment is examined?

Answer 24

Edge standing

Question 25

What does coverage examine?

Answer 25

Does the lens cover the cornea and limbus in all positions of gaze?

Question 26

What beam and brightness is used to examine lens coverage? What is the procedure to check coverage?

Answer 26

Thin beam, bright beam Procedure: Move slit lamp illumination when patient changes fixation

Question 27

What does lag and sag record?

Answer 27

How much the lens resists movement as patient changes fixation. Lag: Horizontal movement Sag: Vertical movement

Question 28

Movement of blink assessed at what mag?

Answer 28

16X

Question 29

What beam and brightness used to determine movement of blink? What should the patient gaze at when assessing this? How is it recorded?

Answer 29

Thin and bright beam used Patient in upgaze - allows to see bottom edge of the lens. Additionally, repeat in primary gaze also. Ask patient to blink and assess the movement. Recorded in mm

Question 30

Why is movement of blink also assessed in primary position especially for toric lenses?

Answer 30

Because toric lenses are thicker at the bottom and can give an artificial movement sometimes

Question 31

What are the different movements seen with Flat lenses compared to steep lens and compared to optimal lenses

Answer 31

FLAT LENSES: lenses moves all of the distance: about 1mm STEEP LENSES: lenses do not move at all: about 0mm OPTIMAL LENSES: Lenses move by 0.25mm- 0.5mm

Question 32

Mag, beam and illumination used for push-up test? What target is used for this test? How is it done?

Answer 32

16x bright beam thin beam target: practioners forehead How it is done: Push the lower lid against the lens gently and release and observe the movement and recovery

Question 33

How is lens comfort identified? How is lens comfort for steep lens vs optimal lenses vs flat lenses

Answer 33

Patient to rate comfort out of 10- ideally should by 8/10 or above Steep lenses: Good comfort initially, but gets uncomfortable with time Flat lenses: uncomfortable especially when patient blinks Optimal: good comfort

Question 34

What are other factors that affect initial lens comfort?

Answer 34

1. Practioner technique 2. Lens thickness 3. Lens modulus 4. Small foreign bodies trapped under the lens

Question 35

How is vision assessed with CL fitting-What is the ideal answer ?

Answer 35

Vision should be clear and stable, little difference observed before and after blink.

Question 36

How does blinking affect vision of steep vs flat lenses?

Answer 36

Steep lenses: vision improves after blink Flat lenses: vision worsens after blink

Question 37

3 external factors that affect lens fit

Answer 37

1. Temperature 2. Humidity 3. Lens hydration

Question 37

What 2 things are recorded in push-up test?

Answer 37

1. How easy it is to move the lens 2. How well the lens recovers

Question 38

How to amend a lens with a steep fit?

Answer 38

1. Increase BC. 2. Try different manufacturer with the same BC.

Question 39

How to amend a lens with a steep fit?

Answer 39

1. Reduce BC. 2. Try different manufacturer with the same BC.