Varifocals Measurements and Markings L3 Flashcards
Features of Enhanced Readers
- Larger intermediate 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. Cosmesis is excellent - it looks like a single vision lens
Varifocals and distortion along the edges
- Known as oblique surface astigmatism
- More of a problem with an increase in add, even if distance vision doesn’t change
- More problematic with driving because px wants to glace over to the side to check mirrors
- When dispensing 1st time and at collection, good communication is key ie where to position hear etc
Best candidates for varifocals?
- People with multitasking jobs who use all vision, distance, intermediate and near vision e.g. like a teacher.
- Previous progressive lens wearers
- Children with accommodative problems
- Those with Low adds
- Individuals who are highly motivated (they really want them
Which patients require consideration (can still be fitted but you just have to consider/communicate a few things before prescribing)?
- Presbyopes with relatively high add >2.25 - Prev wide segment bifocal wearers (remember the width of the segment decreases)
- Individuals sensitive to vertigo or motion sickness (because of the distortion at the sides)
- Those with Anisometropia - due to weight diff and differential prism
- Individuals particularly sensitive to changes in vision
- Eye movers/ people who require wide visual areas
Fitting Procedure for Progressive Lenses
- Select the frame
- Pre adjust the frame
- Measure the fitting heights
- Meaure the distance PDs (monocularly)
- Verify blank size
- Take free form measurements
Measurements when dispensing
- Pupil distance (Must be done monocularly - because not everyone has a symmetrical face - and its important pupils lie in corridor otherwise they will experience distortion).
- Heights
- Panto tilt - so tilt inwards so that bottom of the lens is closest to the eye.
- Face wrap - make sure lens are following curvature of the face (this would involve lens angled in towards ears)
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 lens can fit all 3 rxs
- Pxs require at least 10mm above the eye to the rim for varifocals
Pantoscopic Tilt
- Gives a larger/wider reading section (larger FOV)
- 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 because 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
Why is pupil distance (monocularly) really important?
It dictates which part of the lens the Px looks through.
What do you need to ensure you always do when it comes to fitting varifocals?
Select Frames first then do measurements to ensure that all three segments can fit on the lens in the glasses in accordance with their measurements.
What is the rough standard for Pantoscopic tilt?
10-12 degrees but manufacturers will state their own conditions sometimes.
What is an orthoscopic angle?
When the glasses lie flat - there is no tilt to them.
If a patient complains about a pair of varifocals and you see them having to turn their head to view things what has most likely been done wrong with the precribing of the varifocals?
The PD has been taken incorrectly thus pupils are lying in an area of distortion ( this normally happens because Binocular PD was taken rather than Monocular PD)
What is the misconception with Prism thinning?
The misconception is that its about making the lens thinner when in actuality its about making the lens of even thickness.
Why does the need for prism thinning occur?
As the radii of curvature is always changing throughout lens and getting steeper towards the bottom you will find the top part of the lens tends to be thicker.
In what case does prism thinning not work well?
It works well in majority of classes but will not work well if px has different adds in each eye.
How do you choose a progressive lens?
Find out the needed size and location of the useful areas The width of the corridor and length. Rate of power of change in the corridor.
What are the benefits of single vision glasses?
Often (but not always) cheaper than more complex lenses. Px has a wide segment to view through - good for those e.g. who are prolific readers.
What should you discuss with the px about getting varifocals?
Explain why a patient who tilts their head up when marking up for varifocals may non-tol.
Because thats not their natural viewing position thus all your markings are off and so when px uses the glasses naturally they will be looking through a distortion area.
(Non-tool just means mess up)
