CL - Presbyopic Cl Correction - Week -3

Question 1

What percentage of soft lens fits are for the correction of presbyopia?

Answer 1

25%

Question 2

Name 5 types of presbyopic contact lens corrections

Answer 2

Single-vision near specs over distance CL
Bifocal soft/rigid CL
Multifocal soft/rigid CL
Monovision
Enhanced monovision (bi or multifocal lens in one eye, single vision in other)

Question 3

List 5 general factors to consider when selecting a patient for presbyopic correction with contact lenses

Answer 3

Previous or new lens wearer
Ocular + systemic health
Full time or part time wear
Visual needs
Realistic expectations (desire/necessity for perfect vision)

Question 4

What ocular factors makes a patient a good candidate for presbyopic correction with contact lenses? (4)

Answer 4

Emerging presbyopes
Motivated patients
Existing CL wearers
Low to moderate uncorrected hyperopes

Question 5

What ocular factors makes a patient a more challenging candidate for presbyopic correction with contact lenses? (7)

Answer 5

Emmetrope with early presbyopia
High visual demander
Astig > 0.75 DC (monovision)
Late presbyope with high near demands
High hyperope
Small pupils (simultaneous designs)
Dry eye

Question 6

What sort of baseline data should you acquire for a candidate for presbyopic correction with contact lenses? (6)

Answer 6

Oc. dominance
Pupil size in dim and bright
Accurate refraction: push plus
Slit lamp: thorough tear film evaluation
Corneal topo
CL fitting parameters: Palp aperture, HVID

Question 7

List 3 advantages for distance CLs + glasses

Answer 7

Simplest and cheapest option
Optimum acuity D and N
Maintain distance CL Rx for current wearers

Question 8

List 3 disadvantages for distance CLs + glasses

Answer 8

Desire to avoid specs
Demotivating existing CL wearer
Px needs multiple forms of correction

Question 9

What are the 2 different designs for bifocal and multifocal contact lenses?

Answer 9

Alternating vision - near seg at bottom (RGP lenses designed to mimic bifocals)
Simultaneous vision - distance and near in concentric circles

Question 10

How is the lens stability, position and translation of alternating bifocal contact lenses controlled?

Answer 10

by prism or truncation

Question 11

What is the most important factor in fitting alternating bifocal contact lenses?

Answer 11

Lid tone: the lower lid must be firm and not below the lower limbus

Question 12

List 4 advantages of alternating bifocals

Answer 12

Good distance vision
Good near vision
Good stereo
Similar to spectacle bifocals

Question 13

List 6 disadvantages of alternating bifocals

Answer 13

Unsuitable for patients with lower lid > 1mm below limbus or poor lid tension
Flat fitting lenses will be less comfortable
Lens rotation on down gaze can be a problem
Relative expense
Chair time
No near vision above primary gaze

Question 14

List the 4 fitting principles for alternating bifocal lenses

Answer 14

Aim for alignment of RGP fit (centre the lens with the eye)
Truncation to rest on the lower lid
Don’t fit too steeply
Different designs recommend slightly different placements of the segment

Question 15

What tends to happen if alternating lenses are fitted to steep?

Answer 15

Tend to get a nasal rotation of the near segment

Question 16

In general, where should the near segment of an alternating vision lens be placed in line with?

Answer 16

place segment in line with inferior pupil margin

Question 17

Describe the principles behind simultaneous vision design lenses

Answer 17

D/N zones BOTH in front of the pupil
As fixation is directed to D or N, one zone will produce a focussed image, others will be blurry
Visual system needs to select the clearer image and ‘ignore’ the blurry image

Question 18

Name the 3 main designs for simultaneous vision lenses. Are these designs pupil dependent?

Answer 18

Concentric/Annular
Aspheric
Diffractive

Yes. So performance is dependent on pupil size and whether pupil is centred.

Question 19

In what 2 ways are concentric/annular lenses designed

Answer 19

Bicocentric - 2 circles
Multi-zone concentric - multiple concentric circles. (aka the rinnegan, but not quite as many)

Question 20

How do aspheric lenses differ from concentric lens designs?

Answer 20

Aspheric designs have gradual power changes. So by that notion, have an intermediate zone too

Question 21

How can aspheric lenses be categorised?

Answer 21

Centre-Distance: D in centre, N as you go further periphery
Centre-Near: vice versa

Question 22

Describe how the diffractive design for simultaneous lenses works

Answer 22

The central zone is focused to D through refraction.

Concentric phase plates on the rear surface of the lens split/diffract the light into 2 distinct focal points (one for N, one for D). The lens at each plate has a different refraction, resulting in small jumps in power between plates.

Question 23

What is the main downside to diffractive lens designs?

Answer 23

Some light is lost in the diffractive process, reducing low contrast acuity

Question 24

List the 6 lens fitting principles for simultaneous lenses

Answer 24

Follow manufacturer’s instructions for initial BOZR, BVP, near add
Allow 5 minutes on eye to settle
Use normal fitting criteria for soft lens fitting
Good centration critical
Appropriate lens movement important
Measure VA binocularly in natural free space

Question 25

Why is good centration critical in simultaneous designs?

Answer 25

The optic zone can be very small (2mm). 1mm decentration can cause ghosting/blurring

Question 26

What does a loose fitting simultaneous lens cause? What about tight?

Answer 26

Loose (>0.3 movement): variable vision
Tight (<0.1): lens distortion

Question 27

How can aspheric lenses be combined with monovision?

Answer 27

D centre (N periphery) in one eye. N centre (D periphery) in other eye.

Question 28

What simultaneous lens designs are available for soft disposable contact lenses? (3)

Answer 28

Aspherics
Aspheric + monovision combo
Multi zone concentric designs

Question 29

Describe the simultaneous lens design available for RGPs

Answer 29

Translating concentric bifocal design {menicon menifocal z multifocal RGP}

It has a centre-D with a near surround in steps and is aspherici

Question 30

List 6 advantages of simultaneous lens designs

Answer 30

Reading position useful in positions other than downgaze
Ideal for soft lens material
Available in disposable designs
Si-Hy materials
Some retention of binocularity (stereo)
Area of current CL growth/Research+Development

Question 31

List 3 considerations for simultaneous lens designs

Answer 31

Visual compromise (px needs to accept this, reduced contrast acuity)
Lens centration critical
Most are dependent on pupil size

Question 32

Which eye should receive the distance correction in monovision designs?

Answer 32

The dominant eye

Question 33

What should you assess when prescribing monovision to a patient? (2) How much of the Rx should you prescribe?

Answer 33

Typically the full Rx should be prescribed
Perform BV tests (stereo) to assess effects
Measure binocular D + N VA

Question 34

What does the success of monovision depend on?

Answer 34

Ability of patient to suppress blur

Question 35

For what level of add does monovision tend to be successful for?

Answer 35

Up to 1.75 add

Question 36

How long should fill adaptation to monovision CLs take?

Answer 36

2-3 weeks

Question 37

List 6 advantages of monovision

Answer 37

Ease of fit
Alter only one lens for existing wearers
Less expensive than multifocals
Not dependent on pupil size
Easy correction of astigmatism (correct any cyl >/=0.75)
Complete range of modalities/materials

Question 38

List 6 disadvantages of monovision CLs

Answer 38

Impairs binocularity
Glare sensitivity
Some patients don’t adapt
May require enhancement D or N glasses
Unsuitable for patients with asymmetric VA (eg amblyopia)
Contraindicated for pilots