Soft contact lens fitting

Question 1

What do we need to do before choosing which trial lenses

Answer 1

*Convert spectacle rx to ocular rx
*Choose TD, BVP, BOZR

Question 2

When would you convert to ocular rx

Answer 2

If rx greater than +4.00D

Question 3

When do you need to consider topic or lenticular astigmatism

Answer 3

If cyl is more than 0.75D

Question 4

What can you do if cyl is less than 0.75D

Answer 4

Use mean sphere equivalent

Question 5

What do you want the TD to be

Answer 5

2mm larger than HVID

Question 6

What should you check before fit SCL

Answer 6

Tear film

Question 7

What material should you pick if you see a lot of lipids in tears:

Answer 7

Hydrogel

Question 8

Disadvantage of silicon hydrogen

Answer 8

Attract more lipids

Question 9

What happens if lens fit looks too tight:

Answer 9

*Reduce lens movement
*Nipping of blood vessels
*Staining pattern where lens border was i.e when take lens out, can see border of lens
*This is where the lens border has rubbed the epithelial cells of conjunctiva due to tightness

Question 10

When would you keep same hydrogel material:

Answer 10

*When px doesn’t have any problem with comfort or vision
*No problem with lens material

Question 11

Which lens modality would you choose if px wants full time basis:

Answer 11

One month replacement modality

Question 12

Daily lenses limitations:

Answer 12

*Rx and colours
*Expensive

Question 13

What is important when fitting coloured CLs:

Answer 13

Pupil size in photopic light conditions

Question 14

What is printed on coloured contact lenses

Answer 14

Iris diameter

Question 15

Consequence of large pupil size in photopic conditions:

Answer 15

*When light dims it becomes more mesopic
*Pupil will become larger
*So want largest pupil size in the lens

Question 16

What to look for lid eversion:

Answer 16

*Redness
*Roughness
*Papillae
*Grade these in 0.5mm

Question 17

Lid abnormalities:

Answer 17

*Meibomian gland dysfunction
*Blepharitis
*Grade it

Question 18

Centratio - slit lamp

Answer 18

*White light
*Look for borders of lens
*Don’t manipulate lids

Question 19

Coverage - slit lamp

Answer 19

*Check when doing centration so white light
*Lens should have complete corneal coverage and extend at 0.5mm onto conjunctiva in all directions i.e primary, left, right, up and down
*SO SHOULD COVER WHOLE CORNEA WITH 0.5MM LESS AROUND

Question 20

What will optimum fitted SCL exhibit:

Answer 20

*Good centration
*Moving 0.25 – 0.50mm with each blink

Question 21

Tight lens:

Answer 21

*<0.20mm movement
*Producing conjunctival drag = conjunctiva moves with the lens and the lens movement is little to none
*When removed, the tight lens may leave an impression ring on the sclera at position of lens edge

Question 22

Loose/flat lens:

Answer 22

*Move partly off cornea
*Move >1.00mm

Question 23

Lens lag

Answer 23

• Loose: If lens moves more than 1.00mm
• Tight: If lens less than 0.2mm
• Ideal lens lag:
  Moves up to 1.00mm

Question 24

What does too much sag cause

Answer 24

Lens to drop

Question 25

When is lag best observed:

Answer 25

Superior gaze

Question 26

How to estimate lag:

Answer 26

*In primary gaze, set width of beam to distance between lens border and limbus
*BEAM = 0.5MM

Question 27

Push up test

Answer 27

• Measure of tightness
• Px looks slightly up (lens border free from lid)
• Use finger to put pressure on lower lid
• Move lens vertically
• Allow lens to re-centre
• Judge movement (related to distance between lens border and limbus)

Expected values?
- Correct: slow to move; steady recovery; 40-60%
- Tight: Difficult to move with slow to no recovery, 65-100%
- Loose: Easy movement and fast recovery, 35-0%

Question 28

When should you change the lens for PUT

Question 29

When should you change the lens for push up test

Answer 29

Clinical significant: You must change the lens if PUT >75% or <25%

Question 30

VA

Answer 30

• CL BVP SHOULD REPRESENT FULL OCULAR RX CAUSE IN SCL, NO TEAR LENS POWER BEHIND LENS
• But sometimes there may be “myopic creep” = slow progressive increase in myopia caused by lens induced hypoxia seen in EW/CW

Stable vision:
Good fit

• There is no liquid lens power
• Occasionally +0.50D or -0.50D shift
• Correct: stable VA
• Tight: improves after blink
• Loose: worsens after blink

Question 31

BOZR

Answer 31

• Changes to BOZR have greatest impact on fitting
• Steeper BOR will tighten the fit -> better centration?
• Flatter BOR will loosen the fit

Question 32

TD

Answer 32

• Changes to TD have impact on centration and movement
• Larger TD will DECREASE movement which may help centration
• But remember that they are related to sagittal depth (difficult to predict between manufacturers.

Question 33

Larger TD:

Answer 33

*Decrease movement
*Becomes steeper

Question 34

Smaller TD:

Answer 34

*Increase movement
*Worsen centration

Question 35

Soft contact lens fitting involves

Answer 35

• The selection of the most appropriate lens material, dimensions and wearing modality to match the ocular characteristics and patient needs, whilst
• Giving the best fit and visual acuity with minimal physiological effects

Question 36

Discontinuation SCLs reasons

Answer 36

Discomfort has been shown to be due to a combination of patient and lens factors:
- Patient factors include an irregular or thin tear meniscus, and an increase in conjunctival staining and palpebral roughness
- Lens factors are simply due to poorer centration, and a loose fit
- Sometimes material choice or lens edge

Underlying causes of these contact lens discontinuations is often due to poor fit or inappropriate selection i.e lens moving too much or not centered correctly