CLM - Soft Contact Lens Fitting I - Week 6 Flashcards

1
Q

List the 8 parameters for contact lenses.

A
Back optic zone radius
Total diameter
Back vertex power
Water content
Dk
Material
Design
Thickness
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Define BOZR.

A

Back optic zone radius - radius of curvature of the back surface of the lens (mm)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Define Dk.

A

Amount of oxygen passing through a contact lens meterial over a set amount of time and pressure difference

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Define Dk/t.

A

Amount of oxygen passing through a contact lens of specified thickness over a set amount of time and pressure difference

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

By how much is the BOZr generally flatter than the average K-reading?

A

0.6 to 0.8mm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What does a BOZR that is too flat result in?

A

Poor centration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What does a BOZR that is too steep result in?

A

Reduced lens movement

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Does changing the BOZR of disposable soft lenses greatly alter the lens movement?

A

No

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Can lens designs in the same BOZR have very different movement profiles?

A

Yesd

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Do disposable soft contact lenses generally have many BOZRs?

A

No, generally just one or two

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the average K reading (mm and D)? What BOZRs are mostly expected to fit?

A

7.8mm
43.00D
Expected that most 8.6/8.7mm lenses will fit

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is considered a steep K reading (mm and D)? What BOZRs are mostly expected to fit?

A

<7.5mm
>45.00D
Few brands will have steep BOZRs of 8.3/8.4mm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

To try first, what BOZR should be chosen first and why?

A

Choose the steepest BOZR first to minimise mechanical issues

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How large is the total diameter of a soft lens compared to the iris?

A

Usually 2.0mm greater than the horizontal visible iris diameter (HVID)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What effect does a large total diameter have (2)?

A

Reduced lens movement and inadequate tear exchange

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What effect does a small total diameter have (3)?

A

Excess movement, poor centration, and poor comfort

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Do disposable soft lenses typically have one or many total diamters?

A

Usually just one

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

In what two ways can the back vertex power of a contact lens be measured?

A

Calculated from the spectacle refraction

From over-refraction with a trial contact lens

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is the spherical equivalent? What about if its a toric lens?

A

Sphere + cyl/2

If toric, the BVP must be calculated separately in each meridian

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

For what powers does vertex distance need to be considered when converting between spectacle and contact lenses?

A

≥±4.00D

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is the clinical pearl regarding the choice between contact lenses and spectacles for myopes and hyperopes?

A

Myopes - CLs < GLs

Hyperopes - CLs > GLs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What four factors will the choice of lens material depend on?

A

Desired Dk/t
Deposition profile
Wettability/dry eye issues
Modality

23
Q

What is an advantage of thinner lenses? List 4 disadvantages.

A
Advantage
Maximises oxygen transmissability
Disadvantage
Poor handling by the patient
Lens life is shortened
Thinner lost-lens tear flim, therefore lower movement with blinks
Dessication staining of the cornea
24
Q

Which are thicker, plus or minus lenses? What about sphere vs toric?

A

All plus lenses and toric lenses are relatively thicker

25
What mechanical issues can SiH lenses cause?
GPC
26
Is there a substitute for trialling a soft contact lens on the eye?
No
27
What 4 eyelid factors affect the fit of a contact lens?
Position Tension Blink strength Surface regularity
28
What three eye factors affect the fit of a contact lens?
Topography of the anterior corneal surface HVID Corneal size
29
What 4 lens factors influence the fit of a contact lens?
Sag properties of the lens Lens prescription/thickness Lens material The design - spheric/aspheric, edge profile, peripheral curves etc
30
Whenever possible, what contact lens material should be chosen?
SiH
31
What is the desirable BOZR for a contact lens?
0.6 to 0.8 flatter than the average K reading
32
Define the 2C-MAP mneumonic.
``` Centration Coverage Movement Acuity Push-up ```
33
What two conditions will satisfy lens centration as optimal?
If the lens edge shows uniform and symmetrical overlap onto the sclera in all meridians If the lens is decentred (as with the pushup), it should regain optimal centration in less than a second
34
Define lens lag and the three categories and their cutoffs.
Amount by which the lens trails the movement of the eye <0.2mm - insufficient 0.3mm - 0.7mm - acceptable >0.7mm - excessive
35
What can cause excessive lag and no lag?
Excessive - poor centration | No lag - lens adherence
36
What four factors should be considered with poor lens centration?
BOZR Comfort Visual acuity Lens diameter
37
What is the ideal and acceptable coverage of the cornea by a soft contact lens (in all gazes)?
Ideal - ≥1mm Acceptable - ≥0.5mm Unacceptable - <0.5mm
38
List three reasons why complete corneal coverage is important.
Mechanical - prevents corneal, limbal, and conjunctival trauma Physiological - minimises corneal exposure/dessication/tear film disturbance Comfort
39
What two factors should be considered with poor lens coverage?
Total diameter | BOZR
40
What is lens movement important for?
Promoting post-lens tear film exchange and mixing
41
How is lens movement quantified? List the three categories for it and the measurement.
Vertical change in lens position before and after blinking Inadequate - <0.2mm Excessive movement - >1mm Well-fitting lens - 0.25mm to 0.5mm
42
What is the pushup test? How does a well-fitting lens respond?
Examiner pushes the lens superiorly using the inferior eyelid A well-fitting lens is able to e easily moved and will rapidly return to centre location
43
List four important factors about the post-lens tear film.
Antibacterial Foreign body and debris removal Drives epithelial exfoliation Epithelial nutrition
44
Where is the pre- and post-lens tear flim?
Post - found between the cornea and the lens | Pre - found over the front surface of the contact lens
45
List two important factors of the pre-lens tear flim.
Lubrication of the lids (comfort) | Optics (vision quality)
46
How can the post-lens tear film be observed using the slit lamp (mag, angle, slit width) and how will an optimal fit appear? What about if there is reduced tear exchange?
Specular reflection, high mag, high angle, narrow slit Optimal fit - aqueous (non-coloured) Reduced - coloured/patterned flim
47
In what kind of lenses is lens edge alignment important?
Stiffer higher modulus SiH lenses
48
What is the optimal lens comfort?
Only the slightest awareness of the lens being present
49
What can no sensation of the contact lens be due to?
Lens adherence (too tight)
50
How can lens surface quality be assessed?
Using keratometry or corneal topography
51
Can an abnormal pre- and post-lens tear film distort keratometer mires?
Yes, but only pre-lens
52
What can cause lens settling?
Tear flim trapped behind the soft lens appears to be squeezed out by the initial blinking leading to a reduction in lens movement
53
Is movement immediately upon lens application representative of normal movement?
No, wait 2-3 minutes