6. Progressive Addition Lenses (COMPLETE) Flashcards
what is the purpose of progressive addition lenses? (describe, and what is it used for?)
Provide a spectacle correction for presbyopia in which there is an intermediate zone of variable power between distance and near zones
what are the advantages and disadvantages of progressive additional over bifocals?
Advantages
1. Clear vision at a range of distances
2. No image jump at zone boundaries
3. Superior cosmetic appearance
Disadvantages
1. Narrow intermediate zone
2. Aberrations, distortions in peripheral zone
Orientation of unwanted astigmatism is important
what are the zones of progressive addition lenses? (diagram p.2)
distance, peripheral, intermediate, near.
difference of soft and hard designs of progressive addition lenses? (diagram p.3)
hard designs have larger near and distance
zones, but rate of change of aberration greater. see diagram.
write notes about unwanted-astigmatism rate of change.
Unwanted-astigmatism rate of change
proportional to add power. inversely proportional to corridor length.
what are some inked markings included on progressive lenses? what is it for? (diagram p.4)
Inked markings for alignment and
measurement purpose.
- Prism reference point – checking prism
- Fitting cross (few mm above prism
reference point) - Distance reference point – distance power
- Near reference point – add checked
- Markings to identify R/L lenses
what are some semi-visible etched markings (diagram p.4)
Semi-visible etched markings
Logos to help restore inked markings,
nasal and temporal sides 34 mm apart
Add power code, located below temporal
semi-visible logo
Possibly additional markings under nasal
symbol
write notes about frame selection.
(what is the traditional recommendation of fitting cross to framing bottom?)
(nasal area of eye shape?)
(what has lens development changed with decreased frame sizes?)
(diagram p.5)
Traditionally, it is recommended that
fitting cross to be at least 22mm above
frame bottom. Nasal area of eye shape
should not be restrictive.
With frame sizes decreasing, lens types
have been developed with shorter
corridors so that the height need not be
as great
At expense of more rapidly increasing
unwanted astigmatism, narrower viewing
zones, smaller intermediate zones
write notes about fitting measurements. what measurements are used, how are these measurements taken? describe the processes. (diagram p.6, 7)
Monocular PD’s, height of fitting cross above bottom of frame.
Various methods available for doing this.
1. Penlight to obtain corneal reflexes for distance vision.
Reflex position is marked on plastic tape or plastic gauge attached to front of frame.
2. Photograph to enable co-ordinates to be determined.
3. Lewis, Rodenstock systems
Patient looks at device containing mirrors and reading material. Clinician watches reflections, in mirrors, of corneas,
and marks these on frame front => monocular near PD’s.
Arbitrary amount is added to monocular near PDs to give monocular distance PDs. Fitting cross height measured as for method 1.
name three methods used to measure Monocular PD’s, height of fitting cross above bottom of frame (fitting measurements of progressive addition lenses)
- Penlight to obtain corneal reflexes for distance vision.
Reflex position is marked on plastic tape or plastic gauge attached to front of frame. - Photograph to enable co-ordinates to be determined.
- Lewis, Rodenstock systems
Patient looks at device containing mirrors and reading material. Clinician watches reflections, in mirrors, of corneas,
and marks these on frame front => monocular near PD’s.
Arbitrary amount is added to monocular near PDs to give monocular distance PDs. Fitting cross height measured as for method 1.
describe process of restoration of markings.
Hold lens up to fluorescent light to find and mark logos. Then place lens over manufacturer’s centration chart for the
specific lens to locate the other positions (eg fitting cross)
To replace fluorescent lights, some companies provide light box units to find the logos.
Some lenses have a fluorescent dye at logo positions - located using a light source with near blue light.
list some progressive lens types (companies)
Carl Zeiss Vision: Sola SolaOne, GT2 3D, …
Essilor: Accolade, Accolade Freedom, Comfort New Edition, Varilux
ellipse, …
Hoya: Hoyalux iD Classic, Hoyalux iD MyStyle, Hoyalux iD LifeStyle, …
Other designs by Kodak, Nikon, Opticare, Rodenstock, Shamir, Younger Optics
Designs with short corridors include Essilor Comfort Short New Edition, Hoya Summit CD, Zeiss GT2 3D Short.
Traditional progressive addition lenses fabricated from a semi-finished lens blank i.e. progressive surface finished. Average positions of wear assumed (pantascopic tilt, wrap around and vertex distance
Traditional progressive addition lenses fabricated from a semi-finished lens blank i.e. progressive surface finished. Average positions of wear assumed. what are they?
pantascopic tilt, wrap around and vertex distance
list some company designs with short corridors.
Essilor Comfort Short New Edition, Hoya Summit CD, Zeiss GT2 3D Short.
what is free-form surfacing and what measurements does it need? advantages (what does it take into account)? give some examples of company lenses.
(consider diagram on p.10 check if needed)
Free-form surfacing makes it possible to make individualised lenses. essentially customisation.
Additional measurements are required: vertex distance, pantascopic tilt, face form angle (equipment available for measuring these), even centre of-rotation position.
Take into account frame size, vocational needs.
Essilor’s “Ipseo lens New Edition” requires measurements of relative amounts of head-turn and eye-turn
Some lenses have the progressive surface on the back or split the progressive addition between the two surfaces
