Hi John,
I suggest that, if you are at 20/40 to 20/50, you do not wear any lens for distance - except a minus you keep in your car. If you watch TV, just sit a little closer - until you begin to get better-than 20/40.
Assuming you have 20/50, man people find they can read at 18 inches THROUGH a +1.5 to +2.5 diopter lens (with no minus). They find this value of "plus" by checking in the drug store with plus lenses.
Thus they do not wear a "plus" for watching TV - because there is no reason to do so. But wearing a plus (for near) in an "optical sense", moves that "reading materal" out into the distance. If you did this for ALL close work - it would be like "living out doors" for nine months or so. With the above understood restrictions, the refractive state of the natural eye can change by about +1.0 diopters, thus the person who had the discipline to wear the plus (and only for near) can see his Snellen clear to substantially above 20/40.
Tonight I used my +1.25 glasses over my contacts to watch a few episodes of Flash Gordon on my large-screen TV. The +1.25 glasses have a focal length of 31.5 inches, while the distance to my TV is about 8 feet (96 inches), so the image was fairly blurry. Watching TV, just like reading or working on a computer, is an activity in which for an extended period of time the distance at which we're looking has almost no variation. I think I'm going to get myself a pair of +0.50 glasses (with a focal length of 79 inches) to be used over my contacts so that I can watch TV just beyond my far point.
Have any of you gotten lenses specifically for watching TV?