Originally Posted by
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.
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