What are Progressive Lenses?
"After age 40, no one likes to advertise their age — especially when you start having trouble reading fine print. Thankfully, today's progressive eyeglass lenses make it impossible for others to tell you've reached "bifocal age." Progressive lenses — sometimes called "no-line bifocals" — give you a more youthful appearance by eliminating the visible lines found in bifocal (and trifocal) lenses. But beyond being just a multifocal lens with no visible lines, progressive lenses enable people with presbyopia to again see clearly at all distances.
Bifocal eyeglass lenses have only two powers: one for seeing across the room and the other for seeing up close. Objects in between, like a computer screen or items on a grocery store shelf, often remain blurry with bifocals. To attempt to see objects at this "intermediate" range clearly, bifocal wearers must bob their heads up and down, alternately looking through the top and then the bottom of their bifocals, to determine which part of the lens works better.
Bifocals also put you at greater risk for computer vision syndrome (CVS) when using a computer for extended periods. Bifocal wearers have to sit closer to the screen and tilt their heads back to see through the bottom part of their lenses. This unnatural posture can lead to muscle strain, neck pain and other symptoms of CVS. Progressive lenses more closely mimic the natural vision that you enjoyed before the onset of presbyopia. Instead of providing just two lens powers like bifocals (or three, like trifocals), progressive lenses are true "multifocal" lenses that provide a smooth, seamless progression of many lens powers for clear vision across the room, up close and at all distances in between. With progressive lenses, there's no need to bob your head up and down or adopt uncomfortable postures to see your computer screen or other objects at arm's length. Holding your head in a comfortable position, you can simply look straight ahead to see in the distance, move your eyes slightly downward to view your computer through the intermediate zone and lower your gaze a bit farther to read comfortably up close."
Source - All about Vision