Varifocals Measurements and Markings L3 Flashcards
Features of Enhanced Readers
- Larger int and near
- Restricted distance - good for walking around in an office but not suitable for driving
- Good for office use and as a second pair
- Some get limited peripheral distortion
What is Varifocal?
A progressive surface that varies in curvature to provide a gradual increase in power down along a central corridor
Varifocals and distortion along the edges
- Known as oblique surface astigmatism
- More of a problem with an increase in add, even if distance vision doesnt change
- More problematic with driving
- When dispensing 1st time and at collection, good communication is key ie where to position hear etc
Best candidates for varifocals?
- Older people ( when int is an issue, job requirements, drivers, prev wearers)
- Children with accommodative problems
- Low adds
- Individuals who are highly motivated
Which patients require consideration?
- Presbyopes with relatively high add >2.25
- Prev wide segment bifocal wearers
- Individuals sensitive to vertigo or motion sickness
- Anisometropia - due to weight diff and differential prism
Fitting Procedure for Progressive Lenses
- Select the frame
- Pre adjust the frame
- Measure the fitting heights
- Meaure the distance PDs
- Verify blank size
- Take free form measurements
Measurements when dispensing
- Pupil distance
- Heights
- Panto tilt
- Face wrap
Pupil distance
- More important to do mono PDs with varis due to surface astigmatism
- Mono PDs means setting PDs through that clear corridor
Heights
- Check depth to lower rim from pupil centre to ensure ir can fit all 3 rxs
- Pxs require at least 10mm above the eye to the rim for varis
Pantoscopic Tilt
- Gives a larger/wider reading section
- A good tilt is 10-12 degrees
Face Wrap
= The inclination of the temporal edge of each lens towards the face ensuring that the frame front allows the natural frontal curvature of the skull
- It brings the peripheral distance zone closer to the eye increasing the FOV
- This also moves the peripheral areas of distortion out of the wearers immediate FOV
How can you avoid px not getting along with varis?
- Taking correct measurements
- Making sure px adopts a natural head position when measurements are being taken
- Educate px on what to expect
- Px has reasonable expectations
Why do we require prism thinning in varis?
- To equalise the edge thickness of the finished lens beacuse of the diff curvatures on the lens
- 2/3 of the add base DOWN is worked onto the lens surface, this reduces the thickness at the top of the lens
Four considerations into choosing a progressive lenses
- size and location of the useful areas
- width and length of the corridor
- rate of power change in the corridor
- the location, magnitude and axis of unwanted spherical and cylindrical refractive powers
What is the adaptation period for a varifocal?
1 month
