Power Maps

[jland]

hello to all! could someone please help explain how to read or interpret the Power Maps of progressive lenses? More often, lens designers would give you a power map of their new lenses. What information can you really get out of these maps? Also, both mean power map and cylinder map are always presented. How do you differentiate one from the other? Are these maps able to tell how good a PAL design is?

[obxeyeguy]

Harry C, or Tony G to this thread. Wes, or one of you brilliant other young guys? Fezz? Oh that's right, I said young and bright. :-)

[jhegyi]

Darryl Meister has written a very comprehensive article (and that term does not do it justice) about the optics of progressive lenses:

http://www.opticampus.com/cecourse.p...essive_lenses/

Scroll down about 1/3 the way and there is a section on contour maps. He explains the astigmatism and mean power maps nicely.

[sharpstick777]

There are multiple types of distortion, one that is frequently mapped is "unwanted astigmatism". I hate that term, but look at those areas with high astigmatism as having mutitple or incorrect focal points and therefore unusable. You can use the unwanted astigmatism areas of a lens map to get a feel for where the un-usable vs usable areas of the lens are. Unfortunatly, it will vary by patient but most areas off more than .16 -.20D will be blurry.

The power/ sphere map will tell you where the distance and reading zones effectively fall. Not as effective for intermediate. the reading power may be more forgiving than the distance esp toward the intermediate zones. But again, in the distance most areas that vary more than .18D outside will start to get blurry.

To make them most use you have overlay one with the other.

I wish someone would come out with software to do it automatically though, it wouldn't be hard. These two things don't give all types of distortion but its a great tool to compare lenses.

We are experimenting with a way to map free-form (yes it can be done). I will update when I have more. I don't have access to a ray-tracer myself so its a slow process.

The other to lookfor when comparing lenses is the waviness of the lines, and the symmetry of the lens right to left. to do the latter you would have to reverse the image and overlay a left and right eye.

Hope that helps.

[jland]

Darryl Meister has written a very comprehensive article (and that term does not do it justice) about the optics of progressive lenses:

http://www.opticampus.com/cecourse.p...essive_lenses/

Scroll down about 1/3 the way and there is a section on contour maps. He explains the astigmatism and mean power maps nicely.

Thank you for this. I've read Daryl's article back in the past. I'm wondering how did I missed this part. Thanks so much!

[jland]

There are multiple types of distortion, one that is frequently mapped is "unwanted astigmatism". I hate that term, but look at those areas with high astigmatism as having mutitple or incorrect focal points and therefore unusable. You can use the unwanted astigmatism areas of a lens map to get a feel for where the un-usable vs usable areas of the lens are. Unfortunatly, it will vary by patient but most areas off more than .16 -.20D will be blurry.

The power/ sphere map will tell you where the distance and reading zones effectively fall. Not as effective for intermediate. the reading power may be more forgiving than the distance esp toward the intermediate zones. But again, in the distance most areas that vary more than .18D outside will start to get blurry.

To make them most use you have overlay one with the other.

I wish someone would come out with software to do it automatically though, it wouldn't be hard. These two things don't give all types of distortion but its a great tool to compare lenses.

We are experimenting with a way to map free-form (yes it can be done). I will update when I have more. I don't have access to a ray-tracer myself so its a slow process.

The other to lookfor when comparing lenses is the waviness of the lines, and the symmetry of the lens right to left. to do the latter you would have to reverse the image and overlay a left and right eye.

Hope that helps.

The way you explained it is very practical and completes Daryl's explanation. I really appreciate it sir. Thank you so much!

[Celso Cunha]

There are multiple types of distortion, one that is frequently mapped is "unwanted astigmatism". I hate that term, but look at those areas with high astigmatism as having mutitple or incorrect focal points and therefore unusable. You can use the unwanted astigmatism areas of a lens map to get a feel for where the un-usable vs usable areas of the lens are. Unfortunatly, it will vary by patient but most areas off more than .16 -.20D will be blurry.

The power/ sphere map will tell you where the distance and reading zones effectively fall. Not as effective for intermediate. the reading power may be more forgiving than the distance esp toward the intermediate zones. But again, in the distance most areas that vary more than .18D outside will start to get blurry.

To make them most use you have overlay one with the other.

I wish someone would come out with software to do it automatically though, it wouldn't be hard. These two things don't give all types of distortion but its a great tool to compare lenses.

We are experimenting with a way to map free-form (yes it can be done). I will update when I have more. I don't have access to a ray-tracer myself so its a slow process.

The other to lookfor when comparing lenses is the waviness of the lines, and the symmetry of the lens right to left. to do the latter you would have to reverse the image and overlay a left and right eye.

Hope that helps.

Dear Friend,

The Rotlex Class plus or the FFV makes comparisons of these maps automatically, like a surveyor computerized topography corneal compares old and new.
Regards

[sharpstick777]

Dear Friend,

The Rotlex Class plus or the FFV makes comparisons of these maps automatically, like a surveyor computerized topography corneal compares old and new.
Regards

I will have to put that on my Christmas list. No one will let me play with theirs for long.