CLM - Introduction to Advanced Contact Lenses - PAP Week 1

Question 1

List 10 consideraions when determining whether a patient is a good candidate for contact lenses.

Answer 1

Motivation level
Medications
Prior ocular history
Activities
Occupation
Working environment
Visual tasks
Hygiene
Manual dexterity
Intended wearing schedule

Question 2

List four general clinical indications for contact lenses.

Answer 2

High refractive error
Anisometropia
Presbyopia
Elective paediatric

Question 3

Should pupil diameter be taken when doing a baseline exam for contact lenses?

Answer 3

Yes, high and low illumination

Question 4

Define BOZR. What else is it known as?

Answer 4

Back optic zone radius - also base curve

It is the radius of curvature of the back surface of the lens

Question 5

Define TD.

Answer 5

Total diameter

Full/total contact lens diameter

Question 6

Define BVP.

Answer 6

Back vertex power

Power of a lens

Question 7

Define WC.

Answer 7

Water conent

Percentage of water

Question 8

Define Dk.

Answer 8

Oxygen permeability

Amount of oxygen passing through a contact lens material over a set period of time and pressure difference

Question 9

Define Dk/t.

Answer 9

Oxygen transmissibility

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

Question 10

Give the general format for SCL parameters.

Answer 10

BOZR/TD/BVP

Question 11

How many BOZRs do soft contact lenses tend to have? In what four modalities may it be different (and what number of BOZR)?

Answer 11

Many only have one BOZR
Some have two:
-extended wear
-monthly
-fortnightly
-daily disposables

Question 12

What is an average K reading (both mm and D)? What soft contact lens BOZR is expected to fit this reading?

Answer 12

43.00D or 7.8mm

Expect that most 8.6/7.7mm lenses will fit most eyes

Question 13

What is considered a steep K reading (both mm and D)?

Answer 13

> 45.00D or <7.5mm

Question 14

What BOZR should be chosent to trial first and why (for SiHy lenses)?

Answer 14

To minimise mechanical issues, choose the steepest BOZR

Question 15

What total diameter is generally expected?

Answer 15

Usually >2.00mm of HVID

Question 16

What effect can an excessively large total diameter lens have (2)?

Answer 16

Reduces lens movement

Inadequate tear exchange

Question 17

What effect can a small total diameter lens have (3)?

Answer 17

Excessive movement
Poor centration
Less comfort

Question 18

Are disposables generally available in a large number of total diameters?

Answer 18

No, usually only one available (for a given brand)

Question 19

In what two ways is back vertex power calculated?

Answer 19

From spectacle refraction (taking into account vertex distance)
From over-refraction with a trial contact lens

Question 20

When using a spherical lens, what power is used to account for cyl and how is it calculated?

Answer 20

Using spherical equivalent power using Sphere (D) + 0.5 x Cyl (D)

Question 21

How should BVP be calculated in toric lenses?

Answer 21

It must be calculated separately in each meridian

Question 22

At what dioptre levels would vertex distance need to be taken into account for soft contact lenses?

Answer 22

≥ ±4.00D

Question 23

What is the clinical pearl on whether contact lenses or spectacles provide better VA for myopes and hyperopes?

Answer 23

Myopes
CLs < Glasses
Hyperopes
CLs > Glasses

Question 24

Define the 2C MAP acronym.

Answer 24

Centration
Coverage
Movement
Acuity
Push-up

Question 25

List the three degrees of decentration for a contact lens and list the cutoffs for each.

Answer 25

Mild <0.5mm
Acceptable 0.5mm - 0.8mm
Excessive >0.8mm
Make sure direction of decentration is noted

Question 26

Define lens lag.

Answer 26

The amount that the lens trails the movement of the eye when gaze is directed.

Question 27

List the three degrees of lens lag for a contact lens and list the cutoffs for each.

Answer 27

Insufficient <0.2mm
Acceptable 0.3mm - 0.7mm
Excessive >0.7mm

Question 28

What can excessive lag result in (2)?

Answer 28

Poor centration

Bad optics in gazes

Question 29

What can zero lag result in?

Answer 29

Lens adherence

Question 30

What should be evaluated when checking lens coverage?

Answer 30

Whether or not the lens always completely covers the cornea (including gazes)

Question 31

List the three degrees of lens coverage for a contact lens and list the cutoffs for each.

Answer 31

Ideal ≥1mm (all gazes)
Acceptable ≥0.5mm (all gazes)
Unacceptable <0.5mm (any gaze)

Question 32

What does lens movement promote?

Answer 32

Post-lens tear film exchange and mixing

Question 33

How is lens movement quantified?

Answer 33

Vertical change in lens position before and after a normal blink

Question 34

List the three degrees of lens movement for a contact lens and list the cutoffs for each.

Answer 34

Inadequate <0.2mm
Well-fitting 0.25mm - 0.5mm
Excessive >1.0mm

Question 35

What is checked during a push-up test?

Answer 35

How easily the lens moves a push-up

Question 36

How does a well-fitting lens move with a push-up test?

Answer 36

Moves easily and rapidly and reliably returns to a central location

Question 37

List the two degrees of lens rotation for a toric contact lens and list the cutoffs for each.

Answer 37

<10 degrees acceptable

≥10 degrees requires compensation

Question 38

Describe the LARS acronym for lens rotation compensation.

Answer 38

Left Add Right Subtract

Question 39

What is meant by lens stability for toric soft contact lenses?

Answer 39

Degree of rotation is constant between blinks

Question 40

List three reasons why lens stability may be inadequate.

Answer 40

Stabilisation methods arent working
BOZR is too flat
Diameter is too small

Question 41

Ideally, how long should a clinician wait after applying a contact lens to an eye?

Answer 41

Wait 2-3 minutes for the contact lens to settle