Results 1 to 9 of 9

Thread: The difference between 2 above and 4 above progressive lenses

  1. #1
    OptiBoard Novice
    Join Date
    Dec 2016
    Location
    Yellville AR
    Occupation
    Dispensing Optician
    Posts
    4

    The difference between 2 above and 4 above progressive lenses

    My understanding is that a 2 above 180 progressive design would get the patient into the reading area faster. Is this correct? (Which would then mean that a 4 above would give a longer intermediate zone....)

  2. #2
    Rising Star
    Join Date
    Aug 2016
    Location
    USA
    Occupation
    Dispensing Optician
    Posts
    96
    Not necessarily.

    Generally speaking, the 4mm drop lens will not give a longer intermediate area. However, if you are directly comparing two lenses (one at 2mm drop and one at 4mm drop) in the exact same frame that are variable length, then yes the 4mm drop will have a longer intermediate area in only that specific circumstance.

    It's still best to think of the functional difference between these lenses using the distance fitting cross as a reference point, and understanding that the corridor drop is the point below the distance fitting cross where the power starts to change.

    I hope this makes sense.

  3. #3
    One eye sees, the other feels. OptiBoard Gold Supporter
    Join Date
    Jul 2002
    Location
    Wauwatosa Wi
    Occupation
    Dispensing Optician
    Posts
    4,804
    Quote Originally Posted by DClair View Post
    My understanding is that a 2 above 180 progressive design would get the patient into the reading area faster. Is this correct? (Which would then mean that a 4 above would give a longer intermediate zone....)
    Where the change starts, the rate of change, and corridor length are all independent of the drop. There are short corridor 4mm drops, and long corridors with 2mm drops.

    Wear the lens (yourself and/or on another subject) to determine how the design performs.

    Hope this helps,

    Robert Martellaro
    Roberts Optical Ltd.
    Wauwatosa Wi.
    www.roberts-optical.com
    ~~~~~~~~~~~~~~~~~~
    Science is a way of trying not to fool yourself. - Richard P. Feynman

  4. #4
    Rising Star
    Join Date
    Aug 2016
    Location
    USA
    Occupation
    Dispensing Optician
    Posts
    96
    Quote Originally Posted by Robert Martellaro View Post
    Where the change starts, the rate of change, and corridor length are all independent of the drop.
    I thought this was the very definition of a corridor drop. Have I been educated incorrectly?

  5. #5
    Master OptiBoarder OptiBoard Silver Supporter
    Join Date
    Jul 2008
    Location
    Cincinnati
    Occupation
    Other Optical Manufacturer or Vendor
    Posts
    520
    Quote Originally Posted by DClair View Post
    My understanding is that a 2 above 180 progressive design would get the patient into the reading area faster. Is this correct? (Which would then mean that a 4 above would give a longer intermediate zone....)
    IMHO 2 drops started when frames started getting smaller and narrower. This allowed them to say that what used to be a 18mm minimum fitting height
    could now be used at 16 high. Sorta like marketing 101. Package says NEW read the fine print and it says packaging.

  6. #6
    One eye sees, the other feels. OptiBoard Gold Supporter
    Join Date
    Jul 2002
    Location
    Wauwatosa Wi
    Occupation
    Dispensing Optician
    Posts
    4,804
    Quote Originally Posted by bretk0923 View Post
    I thought this was the very definition of a corridor drop. Have I been educated incorrectly?
    With segmented bifocals, the drop is the distance from the 180 line to the top of the seg. I don't know the history of its use with PALs, but it is equal to the distance from the FC to the PRP/180 line. See...

    https://www.optiboard.com/forums/sho...sive-Lens-Drop

    Quote Originally Posted by Don Gilman View Post
    IMHO 2 drops started when frames started getting smaller and narrower. This allowed them to say that what used to be a 18mm minimum fitting height
    could now be used at 16 high. Sorta like marketing 101. Package says NEW read the fine print and it says packaging.
    It's called the business. Or more accurately, the funny business.
    Roberts Optical Ltd.
    Wauwatosa Wi.
    www.roberts-optical.com
    ~~~~~~~~~~~~~~~~~~
    Science is a way of trying not to fool yourself. - Richard P. Feynman

  7. #7
    Rising Star
    Join Date
    Aug 2016
    Location
    USA
    Occupation
    Dispensing Optician
    Posts
    96
    Quote Originally Posted by Robert Martellaro View Post
    Thanks so much for linking to this post, it provides a lot of clarification. It seems I (like many) have been using the term and assuming that it has serious implications on optical quality, when that is not the case at all, unless the patient in question is sensitive to vertical prism at near. For anyone else seeking clarification on this matter, read Darryl Meister's comment on the thread at the bottom.

  8. #8
    One eye sees, the other feels. OptiBoard Gold Supporter
    Join Date
    Jul 2002
    Location
    Wauwatosa Wi
    Occupation
    Dispensing Optician
    Posts
    4,804
    Quote Originally Posted by bretk0923 View Post
    Thanks so much for linking to this post, it provides a lot of clarification. It seems I (like many) have been using the term and assuming that it has serious implications on optical quality, when that is not the case at all, unless the patient in question is sensitive to vertical prism at near. For anyone else seeking clarification on this matter, read Darryl Meister's comment on the thread at the bottom.
    Your welcome. I checked my blue bible but the only reference to drop is for segment drop related to segmented multifocals. Surprising because that info is needed for a proper troubleshoot.

    Best regards,

    Robert Martellaro
    Roberts Optical Ltd.
    Wauwatosa Wi.
    www.roberts-optical.com
    ~~~~~~~~~~~~~~~~~~
    Science is a way of trying not to fool yourself. - Richard P. Feynman

  9. #9
    Compulsive Truthteller OptiBoard Gold Supporter Uncle Fester's Avatar
    Join Date
    Dec 2004
    Location
    At a position without dimension...
    Occupation
    Dispensing Optician
    Posts
    4,370
    Quote Originally Posted by Don Gilman View Post
    IMHO 2 drops started when frames started getting smaller and narrower. This allowed them to say that what used to be a 18mm minimum fitting height
    could now be used at 16 high. Sorta like marketing 101. Package says NEW read the fine print and it says packaging.
    Remember when the Comfort used to be minimum fit height of 22 turned into 18mm in the 90's(?) when big frames got narrower.

    When Essilor declared the Comfort could now be fit at 18 minimum several guru's eventually found that the "new" design was actually the same one but that 85% of the full add power was close enough so to speak.

    The Comfort Short came along not too long after with a real redesign of corridor length- but adjustments had to be made which affected the feel of the lens. Some patients readily adjusted some not.

    This is where I believe the seidel aberrations come into play in our 2 story sandbox that needs to have a 4 story structure.

    https://www.optiboard.com/forums/sho...andbox+analogy

    Post #8

    Seidel Aberrations:

    http://www.quadibloc.com/science/opt0505.htm
    Last edited by Uncle Fester; 06-10-2019 at 02:09 PM. Reason: tweak...

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. What is difference the progressive lenses have thinning prism or not
    By copland in forum Progressive Lens Discussion Forum
    Replies: 2
    Last Post: 01-08-2010, 03:26 PM
  2. The difference of Transitions on Photochromic lenses Vs. Trivex lenses?
    By IeyeI in forum Smart Lens Technology by Transitions Optical
    Replies: 7
    Last Post: 11-10-2009, 09:09 PM
  3. Difference between progressive and no-line bifocal
    By Leighlee in forum Progressive Lens Discussion Forum
    Replies: 18
    Last Post: 05-03-2008, 11:55 AM
  4. Pc or Nylone Lenses - What's the difference ?
    By nichenation in forum General Optics and Eyecare Discussion Forum
    Replies: 13
    Last Post: 10-21-2006, 08:15 AM
  5. difference in lenses
    By JStrike in forum Just Conversation
    Replies: 5
    Last Post: 09-29-2006, 12:15 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
OptiBoard is proudly sponsored by:
Younger Optics and Vision Equipment