In order to understand the concept of multi focal readers, it's best to review why most people over 45 need reading glasses. In a nutshell, reading glasses help us FOCUS whereas magnifiers make object bigger. Normally, we "focus" when light rays converge (or meet) on the retina in the back of the eyeball. Imagine the retina is like a movie screen. The lens in our eye, like the lens of a projector, helps bend the light so it meets there.
As we get older, the lens loses its shape so the light doesn't bend as it should. If you look at the image, the focus is behind the retina, causing blurriness. This also explains why "newbies" who never before wore reading glasses tend to compensate by holding the object or text farther, which would put the sweet spot right at the retina again. However, our arms can't grown any longer, and that's where readers come into play. The lens of the reading glasses abet the lens in our eye to get those rays to converge at the perfect place on the retina and put everything back in focus.
Today's vision needs are more complicated than they were 30 years ago. One pair of readers is sufficient to help with reading at a set distance of about 14". However, we tend to view our phones and desktops at farther distances, which would require a different lens strength. Also a wider variety of fonts & resolutions require different focuses. Over the past 10 years there have been various solutions in the over-the counter reading glass market. Before that, people would have to get readers custom made by their optician at the cost of at least $100. Then clip ons & dual bifocals arrived on the scene for under $50. Though we have other solutions, today we wanted to review our selection of multi focal no line readers.
As depicted in the above diagram, the lenses have three strengths, the strongest located in the bottom. This corresponds to your "regular" reading glass strength that is used to read books, newspapers, and anything held about 14". The two strengths above are weaker, and meant for farther away objects such as mobile phones and i-pads and even looking across your desk. (spying on your co-workers notes!) There is no "line" between the strengths and the shift from one to another is reported to be remarkably comfortable.
You can also use the different strengths to adjust for font sizes. For example, if the small font is way too tiny for the top of the lens, simply shift your eyes a few millimeters and use the stronger portion of the lens. New technology in lens manufacturing has made it possible to keep the price of these ready-to-wear readers at below $30. At time of writing, 4 styles are available, but we're always on the look out for more.