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.
