Vertex distance vs. corridor length

[Trip]

My understanding suggests that a long vertex distance is better served by a corresponding longer progressive corridor. The logic that the eye is exposed to more of the lens surface, thus indicating that having the power changes occur more slowly will be beneficial. Then of course the opposite holding that a shorter vertex is complimented by a shortening of the progressive corridor.

A recent article I read offered that the opposite of this was the correct path. I am fully comfortable that the author has a deeper understanding than I, but fail to grasp reason why a longer vertex would benefit from a shorter corridor.

Please share your experience, .. thoughts on this.

thanks,

[drk]

I think you're right.

If the plane of the lens is out farther, for a given angular downward rotation of the eye, the arc that is swept is longer. You'd want to match the "normal" downward rotation of the eye with the correct lens add section for that (presumed) distance to the object of regard.

In other words, if you have a shorty sitting out 20 mm and look down just a little (say to hit your computer screen) you'd be getting into the add too far.

Who wrote that piece of crap?

[Paul Smith LDO]

The B value of the frame dimension will have a role to play in the corridor length as well.

[Robert Martellaro]

A shorter back vertex distance is desirable though, especially when the corridor length is optimized for POW. Call your favorite PAL manufacturer to see if it is. If not, use fixed designs of known length to get the near power placed as needed for the individual Rx and client.