No John, it's not a marketing ploy. Actually, it's about saving money. Although we're not talking about regular progressive lenses, they do have some bearing in the matter.
With progressive lenses, imagine an hourglass that's wide at top and bottom, narrow in the middle. The top section is for your normal distance vision. The bottom section is for reading (approx. 18 inches) which is your ADD power added to the distance vision's SPHERE value. The narrow middle section is for intermediate distances (say 3 to 7 feet), which is approx. half of the ADD value added to your distance vision's SPHERE value. It's the narrowness <sp?> of this intermediate section that is the problem. You have to constantly move your head back and forth to read text on a computer screen, instead of just moving your eyes as you normally would. For a casual user, that may not be much of a problem. But, for someone who's at a computer for 8 or more hours a day, you can get a serious crick in your neck. For those people, a pair of single vision lenses with the intermediate vision correction allows them to use their normal eye movement to read the screen instead of their necks. Even if you don't sit at your computer for hours a day, some people just enjoy having a clear field of vision while at the computer. Now they *do* make a specialized progressive lens that is called a computer lens. It has a larger (and wider) intermediate corridor, but at the sacrifice of much of the lenses distance field and are much more expensive than single vision lenses. And, as this group is about saving money on glasses, it just seems more economical to get a single vision pair of intermediate glasses than to pay 5 times as much for a pair of computer progressives that you'd probably only use at the computer anyways. Sorry for being so long winded. :) Hope this helps explain things at bit better. -=# Firewalker #=- On Mar 21, 7:13 pm, John Szlachta <[email protected]> wrote: > What's the story with computer lenses? Is this some kind of marketing > ploy? Why would you wear single vision lenses in anything other than > your full correction? Unless I'm missing that we're talking about > progressive lenses here. > > iPhone > > On Mar 21, 2009, at 8:37 PM, Firewalker <[email protected]> > wrote: > > > > > > >> I just ordered 1 more pair tonight for computer use. > > >> My normal perscription is > > >> OD -3.50 -1.50 X 24 > >> OS -4.50 - 1.50 X 165 add + 2.25 > > >> I ordered for computer > > >> OD -2.50 -1.50 X 24 > >> OS -3.50 -1.50 X 165 > > >> Is that correct? > > > If that ADD +2.25 is for both eyes, and not just for the left eye as > > shown, then yes, that is correct. > > > For the record, computer (or intermediate) glasses would have approx. > > half of the ADD power added to the original SPHERE value. When it's an > > odd number like +2.25, then you'd add either +1.00 or +1.25 to the > > SPHERE value. > > Just remember, if your original SPHERE is a negative (myopia), then > > adding power to it would make the SPHERE go the opposite direction. > > (-3.50 ADD +1.00 = -2.50). > > > -=# Firewalker #=-- Hide quoted text - > > - Show quoted text - --~--~---------~--~----~------------~-------~--~----~ Check us out at the oft-updated http://www.glassyeyes.com! You received this message because you are subscribed to the Google Groups "GlassyEyes" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/glassyeyes?hl=en -~----------~----~----~----~------~----~------~--~---
