(Last modified 3/04/11)
I have myopia combined with astigmatism and age-related diminished inability to focus (presbyopia). I had a pair of glasses made that corrected for four different distances by distributing the distance corrections among the two main lenses and the two bifocals. What is different from the standard bi-focal glasses corrections set-up is that one distance lens is assigned infinity-focus (to take care of sharp distance vision); the other (for the predominant eye for camera users) is assigned one-meter-focus (to take care of the mid-distance normally lost in normal bifocal set-ups, and to optimize one main glasses lens for the camera viewfinder effective viewing distance of about 3.5'); the bifocal in the "infinity" lens is set for about 2' (longer than usual, but useful for the "magazine in lap" distance); and the bifocal in the "one-meter" lens is set for about 1.5' (suitable for most short-term reading and other fairly close viewing - with other glasses being used for extended reading and for computer work, and I remove the glasses for very close work). [Since writing the above, I lost good vision sharpness in the 4' to 6' area due to the effects of further aging and I no longer need optimum correction for camera use, so I have narrowed the differences between the four lens focal lengths by changing the distance corrections to 20', 5', 3', and 2'. While this has moved the minimum distance for sharp vision outward, the loss is minor, and good continuous vision from far to near has been restored. Also, I had a pair of glasses made for computer viewing and most reading, set for the eyes-to-computer-screen distance in both lenses.] This arrangement gives good corrections for four different distances within the usual bifocal-glasses lens arrangement and also smooth transitions between those distances without the usual abrupt large shifts in distance settings between the distance lenses and the inset lenses, and also without the "soft edges and need to point your nose at what you are looking at" characteristics of "lineless" glasses. With the small (25-28mm) flat-top inset lenses set lower than normal, I have complete continuously sharp and smooth focus vision from a bit under 1.5' to infinity (with no sense of "mono-vision" in the four-distance lens settings since the correction "errors" between them are minor), good "mid-distance" vision (which is often missing from standard bifocals), a sharp view of the camera viewfinder (normally missing), and wide-angle vision (unlike with narrow-angle "lineless" or "progressive" lens glasses which limit horizontal sharpness - and unlike with standard bifocals with the bifocal inset lenses set for too short a viewing distance, or made too large to see distant things around them, or set too high for a good optimization of sharpness corrections in the vertical direction). It took about 2 weeks to feel comfortable with night driving and movie watching (the camera eye tends at first to predominate when it is dark, or when the subject does not have a lot of well-defined detail, but closing the predominant eye for a moment corrects this) - but for everything now, continuous sharp focus over a wide range of distances and angles has been restored.
It is hard to get some optometrists to "break the rules" and set the small bifocal insets lower than normal (and properly "tilt" the straight top edges for least visibility) and have the distances set for something other than what is too close for anything but an "up near your nose" reading distance (let alone set one of the main lenses "wrong") - but it is worth the effort to find one that will. I have been using glasses made this way for about 20 years, and they continue to work well for me and they provide noticeable improvements in vision compared with the alternatives...
"Hope This Helps"
David Ruether (firstname.lastname@example.org)