Bifocal wearers (such as Mrs. Bob) have a problem with stairs: namely, that on the way down, the staircase falls within the part of the lens which is optimised for close work. Result? "Missed Step" Syndrome, or worse, "Did You Miss A Step? No, I Hit Every One" Syndrome.
An additional, related hazard is when a sign warns of low headroom over the stairway; then, the sign falls within the long distance part of the lens and may be missed. Result? "Ouch My Aching Head" syndrome.
Therefore I propose Inverted Bifocals. In their simplest form, nothing more than an additional pair of spectacles with the same prescription as the regular pair, but with lenses inverted. No more missed steps, no more banged heads. Don't forget to swap them back again once you're back on the ground floor.
A possible high-tech alternative is rotating lenses which can be rapidly turned 180 degrees through a precision gearing system. It's called high-tech not because it's difficult to do, but because only high-tech people and Harry Potter would be seen in public wearing specs with round lenses.-- English Bob, Feb 11 2010 Howabout glasses with a symmetrical top-bottom form factor? The arms would be a bit unusual-looking, and the weight certainly wouldn't be ideal...
"Come here and kiss your grandmummy, oh my, how you've..... shrunk? Wait a minute..."<flips glasses over>-- RayfordSteele, Feb 11 2010 [+] I like the rotating-round-lenses idea, because you could have intermediate orientations between 0 and 180 degrees. Great for reading while lying on one side. There would also be a niche market for people with torticollis.-- mouseposture, Feb 12 2010 I like this idea...today I picked up my new bi-focals..they totally suck....they are the "blended" kind and I find there is only a very narrow place in the lens that gives me good vision. I bought three pairs of glasses in this purchase..one bifocal (I will probably never use) and one "reading" and one "Long vision"...I am going back to the old way...I'll just switch glasses as I need ...I'm very happy with that and I love the great vision I get with just the "all of one kind" type lens.
As for the "rotating" lens...I actually like it...I think it may have merit. But, I think of each lens like a figure "8"...the lenses rotate with the touch of a remote control...you only see through the bottom of the "8"...you want to read, touch the button and 'flip', the lenses change. You want long range vision, touch the button...'flip'...you could wear the "button" on your wrist like a watch.
As for looks, I'm too old to care how it looks...I just want to see clearly.-- Blisterbob, Feb 12 2010 And of course a special bifocal for seeing backwards through door peep holes -- For Tom.-- popbottle, Mar 17 2017 Automatic gearing combined with computer recognition of stairs should be trivial.-- Voice, Mar 17 2017 How about one part of the lens being a separate piece, placed in front of the main lens, that can slide up and down within the frame?-- Size_Mick, Mar 17 2017 random, halfbakery