CLM - Presbyopic CL Fitting - PAP Week 1 Flashcards
List the 5 types of presbyopic corrections available with contact lenses.
Single-vision near spectacles worn over distance contact lenses
Bifocal soft/rigid lenses
Multifocal soft/rigid lenses
Monovision
Enhanced monovision (bi/multifocal lenses in one eye, single vision lenses in the other eye)
What 5 drugs can reduce tear volume?
Ibuprofen
Oestrogen
Antihypertensives
Antidepressants
Antihistamines
List 4 good candidates for presbyopic contact lenses.
Emerging presbyopes
Motivated patients
Existing contact lens wearers
Low to moderate uncorrected hyperopia
Does astigmatism present a challenge when determining a candidate for presbyopic fitting?
Yes, individuals with >0.75D are more challenging candidates
List 5 baseline data needed when doing a presbyopic fitting.
Ocular dominance
Pupil size bright and dim
Accuate refraction - push plus
Slit lamp examination
Corneal topography
List two advantages of using distance contact lenses with near vision spectacles worn over.
Simple and least expensive option
Optimum acuity for D and N
List three disadvantages of using distance contact lenses with near vision spectacles worn over.
There may be a desire to avoid glasses
Demotivating existing CL wearer
Patient needs multiple forms of correction
What is an alternating vision design for presbyopic contact lenses? What about simultaneous vision designs?
Alternating - like a bifocal, but in CL form, bottom half is near Rx
Simultaneous - concentric rings of distance and near Rx
Are alternating vision designs used in soft or rigid contact lenses?
RGPs
Describe how an alternating vision design lens can provide distance and near vision.
It translates up and down with gaze. When looking at a distance, the distance Rx is over the pupil.
When looking down, the lens rides up on the lower lid, and the near Rx is over the pupil.
How are alternating vision design contact lenses stabilised (2)? What is the most important factor with this and why?
Prism or truncation
Adequate lid tone is the most important factor
The lower lid must be firm and not below the lower limbus
List the four lens fitting principles for alternating vision design lenses.
Aim for an alignment RGP fit
-centre the lens with the eye
Truncation to rest on the lower lid
Dont fit too steeply
Different designs recommend slightly different placement of the segment
What tends to happen if alternating vision design lenses are too steep?
Tend to get a nasal rotation of the near segment
In general, where should the near segment of an alternating vision design lens be placed in line with?
In line with the inferior pupil margin
List four advantages of alternating vision design lenses.
Good distance vision
Good near vision
Good stereopsis
Similar to spectacle bifocals
List six disadvantages of alternating vision design lenses.
Unsuitable for patients with lower lid >1mm below the limbus or poor lid tension
Flat fitting lenses will be less comfortable
Lens rotation on down gaze can be problematic
Relative expense
Chair time
No near vision above primary gaze
Describe the principle behind simultaneous vision design lenses.
Distance and near zones are both in front of the pupil
As fixation is directed to either N or D, one zone will produce a focussed image, the others will be blurry
Visual system needs to select the clearer image and ignore the blurry image
List the three main designs for simultaenous vision design lenses and note whether they are pupil-dependent or independent.
Concentric/annular
Aspheric
Diffractive
All of these are pupil-dependent
Describe how a biconcentric design works and what it looks like for a simultaneous vision lens. What does the performance of this design depend on?
It consists of only two regions, an inner circle and outer circumscribing ring
One of these regions is distance Rx and the other is near Rx
There is no intermediate zone
Performance is dependent on pupil size
Consider a multi-zone concentric design for a simultaneous vision lens. What kind of vision distance does it favour and under what lighting conditions (2)?
Favours distance in extreme high and low lighting
Describe aspheric designs for simultaneous vision lenses and how it differs to biconcentric designs.
Similar to biconcentric designs, but with a gradual power change
Describe the two types of biconcentric and aspheric lens designs for simultaneous vision lenses.
Centre-distance
Centre-near
Briefly describe the diffractive design for simultaenous vision lenses.
Central zone focusses distance through refraction
Diffractive zone plate on the back of the lens split light into two distinct focal points
Refraction and diffraction is used to corect near vision
What happens to contrast acuity with diffractive design simultaneous vision lenses and why?
Some light is lost in the diffractive proccess, reducing low contrast acuity.
How should BOZR, BVP, and/or near add be selected? How long should a clinician wait for the contact lens to settle once on the eye? What criteria should be used for fitting if a soft presbyopic contact lens?
Follow manufacturer’s instructions to select initial BOZR, BVP, and/or near add.
Allow 5+ minutes to allow lens to settle.
Use normal fitting criteria for soft lens fitting.
Should a phoropter be used to measure visual acuity?
No
Consider the aspheric design for simultaneous vision lenses. In what eye should the centre-distance and centre-near lens be placed?
Centre-distance (D lens) should be placed in the dominant eye
Centre-near (N lens) should be placed in the non-dominant eye
List six advantages of simultaneous vision design lenses.
Reading position in useful positions other than down gaze
Ideal for soft lens materials
Available in disposable designs
SiHy materials
Some retention of binocularity
Area of current CL grown and R&D
List three considerations for simultaneous vision design lenses.
Requires patient to accept a visual compromise
Lens centration is critical
Most designs are very dependent on pupil size
Describe how monovision corrects for near vision.
One eye is prescribed for distance Rx, the other for near
What is the reported success rate of monovision?
70-75%
Which is more popular, multifocal CLs or monovision?
Multifocals
Which eye should be given the distance Rx in monovision?
The dominant eye
Once monovision is prescribed, what tests should be done?
BV tests to determine the effects on BV and stereopsis
What does the success of monovision depend on?
The ability to suppress blur
What increases the difficulty of success in monovision?
Higher near addition
Up to what D does monovision tend to be successful?
Up to +1.75D
How long can one expect full adaptation to monovision to occur?
2-3 weeks
List 6 advantages of monovision.
Easy to fit
Alter only one lens for existing wearers
Less expensive than multifocals
Not dependent on pupil size
Correction of astigmatism easy
Complete range of lens modality/materials
List 5 disadvantages of monovision.
Deliberate impairment of binocularity
Glare sensitivity, especially night driving
Some patients do not adapt
May require enhancement D/N glasses
Unsuitable for patients with asymmetric VA
Is monovision an indication or contraindication for pilots needing near correction?
Contraindication
Compare vision for distance, intermediate, and near for multifocals and monovision.
Monovision is better for distance and near
Intermediate is the same
Compare stereoacuity and range of clear vision for multifocals and monovision.
Both are better wih multifocals
Do patients generally prefer multifocals or monovision?
Multifocals (thought to be a threefold preference)
How can monovision be combined with multifocals?
By putting a centre-distance lens on the dominant eye and centre-near lens on the non-dominant eye
