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....)
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....)
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.
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.Quote:
Originally Posted by DClair
Wear the lens (yourself and/or on another subject) to determine how the design performs.
Hope this helps,
Robert Martellaro
I thought this was the very definition of a corridor drop. Have I been educated incorrectly?Quote:
Originally Posted by Robert Martellaro
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 heightQuote:
Originally Posted by DClair
could now be used at 16 high. Sorta like marketing 101. Package says NEW read the fine print and it says packaging.
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...Quote:
Originally Posted by bretk0923
https://www.optiboard.com/forums/sho...sive-Lens-Drop
It's called the business. Or more accurately, the funny business.Quote:
Originally Posted by Don Gilman
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.Quote:
Originally Posted by Robert Martellaro
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.Quote:
Originally Posted by bretk0923
Best regards,
Robert Martellaro
Remember when the Comfort used to be minimum fit height of 22 turned into 18mm in the 90's(?) when big frames got narrower.Quote:
Originally Posted by Don Gilman
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