Results 1 to 2 of 2

Thread: Prism on progressive lens

  1. #1
    Bad address email on file
    Join Date
    Jun 2005
    Location
    Asia
    Occupation
    Other Optical Manufacturer or Vendor
    Posts
    31

    Prism on progressive lens

    Hi all,

    I would like to enquire what is the tolerance level for the amount of horizontal prisms that is present when i measure the progressive lens on the distant zone circle.

    What are the limits?

    Because i have encountered a few pairs which shows the following readings when i check through the lensmeter (when no prisms were requested) :

    Example:

    R) 2.5D BI
    L) 2.4D BO

    Shouldn't they be as close to 0 as possible?

  2. #2
    Objection! OptiBoard Gold Supporter shanbaum's Avatar
    Join Date
    May 2000
    Location
    Manchester, CT USA
    Occupation
    Other Optical Manufacturer or Vendor
    Posts
    2,976
    Quote Originally Posted by Iakwin
    Hi all,

    I would like to enquire what is the tolerance level for the amount of horizontal prisms that is present when i measure the progressive lens on the distant zone circle.

    What are the limits?

    Because i have encountered a few pairs which shows the following readings when i check through the lensmeter (when no prisms were requested) :

    Example:

    R) 2.5D BI
    L) 2.4D BO

    Shouldn't they be as close to 0 as possible?
    You don't measure prism at the Distance Reference Point (that's the correct term for the power-checking area indicated by a semi-circle in the distance zone). Measure prism at the Prism Reference Point, which is usually indicated by a dot located at the midpoint between the semi-visible engravings (though Zeiss tends to locate theirs 2.0mm below that point).

    Some amount of base-down prism is usually found at the PRP, and if "thinning prism" has been applied, there may be quite a bit (one-half to two-thirds of the add power or more).

    The applicable tolerance varies, depending on jurisdiction (I don't know what applies in Singapore, but I'd sure as heck observe it).

Thread Information

Users Browsing this Thread

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

Similar Threads

  1. Take a Master Exam
    By Darryl Meister in forum Ophthalmic Optics
    Replies: 130
    Last Post: 07-19-2022, 02:32 AM
  2. Dispensing Aspheric lenses
    By QDO1 in forum General Optics and Eyecare Discussion Forum
    Replies: 1
    Last Post: 07-12-2016, 06:11 PM
  3. Essilor Announces Industry Changing Progressive Addition Lens
    By Newsroom in forum Optical Industry News
    Replies: 0
    Last Post: 01-13-2006, 02:17 PM
  4. Zeiss Introduces Customized Progressive Lens
    By Newsroom in forum Optical Industry News
    Replies: 0
    Last Post: 07-23-2003, 05:36 PM
  5. Replies: 0
    Last Post: 05-20-2003, 04:06 PM

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
  •