'Power' variable clarification on NPD equation

[Hayde]

Found some handy NPD calculations here on Optiboard. (drk's 95% sure is alluring!)

But let's say I'm using:

NPD=DPD -(DPD/[1+W{1/s-F/1000}])

When calculating for power "F", do I use the 180 axis as the reference for factoring in cylinder power? This seems intuitively correct to me, but since reading segments are dropped below eye level to some degree, I feel inclined to try and outsmart myself.

Thanks for the assist.

[HarryChiling]

Found some handy NPD calculations here on Optiboard. (drk's 95% sure is alluring!)

But let's say I'm using:

NPD=DPD -(DPD/[1+W{1/s-F/1000}])

When calculating for power "F", do I use the 180 axis as the reference for factoring in cylinder power? This seems intuitively correct to me, but since reading segments are dropped below eye level to some degree, I feel inclined to try and outsmart myself.

Thanks for the assist.

DPD = monocular distance pd
w = working distance in mm
s = back of the lens to center of rotation of the eye in mm
f = focal length in mm (power along the 180)



From System for Ophthalmic Dispensing. page 38 old book

[Hayde]

DPD = monocular distance pd
w = working distance in mm
s = back of the lens to center of rotation of the eye in mm
f = focal length in mm (power along the 180)



From System for Ophthalmic Dispensing. page 38 old book

Fabulous, thanks Harry!

Looks like it's page 34 in the new edition.

(Serves me right for not remembering to look there first.)

[HarryChiling]

Fabulous, thanks Harry!

Looks like it's page 34 in the new edition.

(Serves me right for not remembering to look there first.)

I keep the old @ work, new @ home.