Differences between Segment Heights and Pupil Heights? And Box Centre Measurements

[rj45]

Hi there,

This is probably a dumb question but I need to be sure. A segment height is not always from the pupil to the lowest part of the frame i.e. in the case of bifocals. But pupil height must always be from the pupil to the lowest part of frame? Is there any other scenario where they are different?
Also whats the significance of a Box Centre Measurement? I understand it can be used to calculate the Blank Size needed, but couldn't I just use the A, B, ED and PD, DBL measurements?
Why would I need to know the geometric centre of the lens/frame etc. when all I need are these measurements?

Thanks in advance Everyone

RJ

[Dr. Bill Stacy]

I think for lined multifocals segment height is from the highest point of the segment to the lowest point of the LENS, and for progressives is from the fitting cross to the lowest point of the lens, in both cases measuring along the vertical, or "box" measurement method, never diagonally. I don't use the term "pupil height" at all, nor do I consider the box center measurement when the A,B,DBL and ED are known.

[Robert Martellaro]

Hi there,

This is probably a dumb question but I need to be sure. A segment height is not always from the pupil to the lowest part of the frame i.e. in the case of bifocals. But pupil height must always be from the pupil to the lowest part of frame?

Yes, center pupil/corneal reflex to the bottommost apex of the lens bevel.

Is there any other scenario where they are different?

I can't think of one.

Also whats the significance of a Box Centre Measurement? I understand it can be used to calculate the Blank Size needed, but couldn't I just use the A, B, ED and PD, DBL measurements?
Why would I need to know the geometric centre of the lens/frame etc. when all I need are these measurements?

Standardization, and for the correct values including a datum line, especially when replacing lenses only. In the link below, note how if the right lens is turned, all of the values change, and the segment is off-axis.

http://www.laramyk.com/resources/edu...boxing-system/

Thanks in advance Everyone

RJ

Your welcome.

I don't use the term "pupil height" at all,

Some of us used to use the term vertical OC height, but that does not necessarily tell us where the pupil center is located. Pupil height does, and should be used when asked for, usually for aspheric/atoric SV and segmented multifocals. I still use vertical OC height, but not when the lens designer wants to know the center pupil location.

[Dr. Bill Stacy]

Interesting, I've been in practice 46 years and nobody has ever asked me for a "pupil height". I see OC ht on every lab form I use, but this is the first time I've heard of "pupil height". I can't imagine turning over the design of a lens to someone who wants to trump my positioning of the seg height or OC ht.

[Tallboy]

Interesting, I've been in practice 46 years and nobody has ever asked me for a "pupil height". I see OC ht on every lab form I use, but this is the first time I've heard of "pupil height". I can't imagine turning over the design of a lens to someone who wants to trump my positioning of the seg height or OC ht.

Any compensated lens with yoked vertical prism involved in the design is choosing a design based off of the "pupil height" you entered into their "OC" column on the lab entry form. It is ridiculously confusing that sometimes OC means where we actually want the OC and sometimes we are just telling software where the patient's pupil is in relation to the lens. It is ridiculous, but the way "its always been done".

I often place the OC in the frame fit by those working on my floor at a slightly different height than they ordered - because I know they all mean pupil height and don't actually think about where the OC is in relation to a pupil for best fit/aesthetics/rotation of the Eye's gaze along an aspheric lens.