11 - Progressive Lenses (Exam 3) Flashcards
Can add power of progressive lenses be measured by a lens clock?
No
Aspheric curvature gradually changes from distance to near
What is the function of an astigmatic contour plot?
Shows distribution and amount of cylinder
Outlines functional areas of the lens
What is the formula for calculating spherical equivalent?
Sphere + 1/2 cylinder
What does each line of an astigmatic contour plot usually represent?
0.50 D increment of power
What does each line of a mean power plot usually represent?
0.50 D increment of power
What does an eye-path power profile graph the relationship of?
Power from the fitting cross through the channel and into the near zone
In an eye-path power profile, what % of add power reveals the true corridor length?
95%
What are 4 design parameters of progressive lenses?
- Add power
- Corridor length
- Near zone width
- Distance zone characteristics
Does the “ultimate” progressive exist?
NO
What does a wide, clear distance zone in a progressive lens produce?
Hard design
Hard line of cylinder along the horizontal axis
Lots of astigmatism below horizontal axis
What does a wide intermediate channel in a progressive lens produce?
Soft design
Cylinder introduced into distance zone
Very long corridor
What does a wide near zone in a progressive lens produce?
Excessive amounts of blur
“Swimming” sensation
At what distance are wearers of progressive lenses most sensitive to blur?
Distance (rather than near or intermediate)
Especially with moving objects
As add power increases, what happens to the near zone?
It decreases in size
What is a basic explanation of rotational PALs?
Lens used for both eyes
Twisted so near zone was inset for each eye
What is a basic explanation of multi-design PALs?
Near zone inset greater with higher add power
‘One design fits all’
Assumes patient’s visual needs are based solely on add power
What is a basic explanation of mono-design (family) PALs?
Designs are consistent
Patient only needs to adapt to change in add if they get new lenses and stay in the same design
Require more thought from the practitioner
How do progressive lenses maximize the distance field of view?
Congruent distance viewing zones
Where should unwanted cylinder be repositioned in a hyperopic Rx?
Distance portion of lens
Where should unwanted cylinder be repositioned in a myopic Rx?
Near portion of lens
What types of patients are the most difficult to be successful with in progressive lenses?
Emmetropes
Not used to having compromised vision at any distance
What type of lenses can be used to make digitally surfaced PALs?
Semi-finished single vision lenses
What are 4 goals of digital lenses?
- Maximized visual acuity at all distances
- Wider intermediate and near zones
- Minimal ‘swim’
- Wider field of view
What is a large advantage of digital progressive lenses for laboratories?
Reduced cost
Due to reduced need for inventory of semi-finished PALs
Semi-finished single vision lenses (much cheaper) can be used
What is the range of fitting heights today for digital lenses?
Greater than 11 mm
What type of optical materials are available for freeform lenses?
Everything except for glass
What are the general power ranges of freeform lenses?
+6.00D to -10.00D sphere
Up to 4.00D cylinder
Not strict limits
What is a general range of costs for freeform lenses?
$225 to $800
What is the ‘best lens’ on the market today?
Freeform (digital) lenses
What must you do when selecting a frame for PALs?
Pre-adjust the frame
What type of PD measurement should you use for PALs?
Monocular
What 3 things result in PALs as add power increases?
- Unwanted cylinder increases
- Near zone width decreases
- Intermediate zone width decreases
What types of patients require more time to acclimate to PALs?
Patients with high add power
Patients with high distance correction
What type of design option is unique to Shamir?
Fixed vs. variable corridors
How should you choose a fixed corridor length?
Closest number to seg height
How would a Fixed 11 lens compar to a Fixed 18 lens
Fixed 11 has almost no intermediate compared to Fixed 18
What type of fixed lens would be ideal for converting a bifocal wearer to PALs?
Fixed 11
What type of fixed lens would be ideal for converting a trifocal wearer to PALs?
Fixed 13
When should variable corridor designs be used?
Very deep frames (seg height >18mm)
Do variable corridor designs give good zone transition?
No
Comparing soft design to hard design PALs, which are easier to acclimate to?
Soft design
because of less unwanted cylinder
What is the purpose of prism thinning in PALs?
Reduce lens thickness in the near zone to improve cosmetics
Occurs in most PALs
Where is the only location in progressive lenses that prism power can be accurately measured?
Prism Reference Point (PRP)
What is the tool used for identifying PALs and where is it available?
Progressive Lens Identifier
The Vision Council
What is the Progressive Lens Identifier useful for?
Finding the fitting cross location of a given lens design
All are slightly different
What is the variance in fitting cross location in different styles of PALs?
On the datum line to 6 mm above the datum line
What is the datum line?
B measurement divided by 2
Currently, how many markings are there on digital PALs?
Between 8 and 12
Where is the add power engraved on PALs?
Temporal side
Where is the manufacturer’s logo engraved on PALs?
Nasal side
What type of engraving denotes a short design PAL?
An asterisk
What are 2 things essential to correcting fitting all PALs?
- Monocular distance PD measurement
2. Pre-adjust the frame
What is 1 essential part of pre-adjusting the frame?
Nosepads
How many PAL design choices are available today?
Over 2000
Who is the top PAL manufacturer in the USA?
Essilor/Shamir
What type of PALs are used for work from 16” to 6’?
Computer lenses
What are 3 considerations to make with frames for PALs?
- Deeper is better
- Avoid aviator styles
- Nose pads are always desireable
Where should the fitting cross be located when adjusting a frame with PALs to a patient?
Pupil center
What must you do with a patient having trouble with PALs?
Remark the lenses
What are the 3 magical adjustments for a trouble progressive lens patient?
- Increase pantoscopic angle
- Increase faceform
- Reduce vertex distance
