CL - Presbyopic Cl Correction - Week -3 Flashcards
What percentage of soft lens fits are for the correction of presbyopia?
25%
Name 5 types of presbyopic contact lens corrections
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)
List 5 general factors to consider when selecting a patient for presbyopic correction with contact lenses
Previous or new lens wearer
Ocular + systemic health
Full time or part time wear
Visual needs
Realistic expectations (desire/necessity for perfect vision)
What ocular factors makes a patient a good candidate for presbyopic correction with contact lenses? (4)
Emerging presbyopes
Motivated patients
Existing CL wearers
Low to moderate uncorrected hyperopes
What ocular factors makes a patient a more challenging candidate for presbyopic correction with contact lenses? (7)
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
What sort of baseline data should you acquire for a candidate for presbyopic correction with contact lenses? (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
List 3 advantages for distance CLs + glasses
Simplest and cheapest option
Optimum acuity D and N
Maintain distance CL Rx for current wearers
List 3 disadvantages for distance CLs + glasses
Desire to avoid specs
Demotivating existing CL wearer
Px needs multiple forms of correction
What are the 2 different designs for bifocal and multifocal contact lenses?
Alternating vision - near seg at bottom (RGP lenses designed to mimic bifocals)
Simultaneous vision - distance and near in concentric circles
How is the lens stability, position and translation of alternating bifocal contact lenses controlled?
by prism or truncation
What is the most important factor in fitting alternating bifocal contact lenses?
Lid tone: the lower lid must be firm and not below the lower limbus
List 4 advantages of alternating bifocals
Good distance vision
Good near vision
Good stereo
Similar to spectacle bifocals
List 6 disadvantages of alternating bifocals
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
List the 4 fitting principles for alternating bifocal lenses
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
What tends to happen if alternating lenses are fitted to steep?
Tend to get a nasal rotation of the near segment
In general, where should the near segment of an alternating vision lens be placed in line with?
place segment in line with inferior pupil margin
Describe the principles behind simultaneous vision design lenses
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
Name the 3 main designs for simultaneous vision lenses. Are these designs pupil dependent?
Concentric/Annular
Aspheric
Diffractive
Yes. So performance is dependent on pupil size and whether pupil is centred.
In what 2 ways are concentric/annular lenses designed
Bicocentric - 2 circles
Multi-zone concentric - multiple concentric circles. (aka the rinnegan, but not quite as many)
How do aspheric lenses differ from concentric lens designs?
Aspheric designs have gradual power changes. So by that notion, have an intermediate zone too
How can aspheric lenses be categorised?
Centre-Distance: D in centre, N as you go further periphery
Centre-Near: vice versa
Describe how the diffractive design for simultaneous lenses works
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.
What is the main downside to diffractive lens designs?
Some light is lost in the diffractive process, reducing low contrast acuity
List the 6 lens fitting principles for simultaneous lenses
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
Why is good centration critical in simultaneous designs?
The optic zone can be very small (2mm). 1mm decentration can cause ghosting/blurring
What does a loose fitting simultaneous lens cause? What about tight?
Loose (>0.3 movement): variable vision
Tight (<0.1): lens distortion
How can aspheric lenses be combined with monovision?
D centre (N periphery) in one eye. N centre (D periphery) in other eye.
What simultaneous lens designs are available for soft disposable contact lenses? (3)
Aspherics
Aspheric + monovision combo
Multi zone concentric designs
Describe the simultaneous lens design available for RGPs
Translating concentric bifocal design {menicon menifocal z multifocal RGP}
It has a centre-D with a near surround in steps and is aspherici
List 6 advantages of simultaneous lens designs
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
List 3 considerations for simultaneous lens designs
Visual compromise (px needs to accept this, reduced contrast acuity)
Lens centration critical
Most are dependent on pupil size
Which eye should receive the distance correction in monovision designs?
The dominant eye
What should you assess when prescribing monovision to a patient? (2) How much of the Rx should you prescribe?
Typically the full Rx should be prescribed
Perform BV tests (stereo) to assess effects
Measure binocular D + N VA
What does the success of monovision depend on?
Ability of patient to suppress blur
For what level of add does monovision tend to be successful for?
Up to 1.75 add
How long should fill adaptation to monovision CLs take?
2-3 weeks
List 6 advantages of monovision
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
List 6 disadvantages of monovision CLs
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
