I’m going to be as brief as I can. I could write pages on this topic. Buying progressive lenses twice over a few years has been the worst retail experience of my life. The dispensers are like clothes salespeople and other retail stores: get the customer out the door as fast as possible. Unfortunately that didn’t suit my style and so I had to become my own expert. I won’t write generally but will try to address your specific problem.
I have scanned the earlier comments and didn’t see all that much that is useful to you. (Sorry, other posters, I said _scanned_.)
First: There are _hundreds_ of progressive lens designs, and probably thousands of patents. Most dispensers have found that they have a decent success rate with a particular design; for all I know, they might have a bulk rate from a manufacturer. If the lens does not suit you, take them back and ask for another design. Any respectable dispenser will tolerate this—they won’t love you, but they will tolerate it. On my first go-round, I had four different designs, but then the lab screwed up at least one or two.
Some designs are quite crappy. There has been a lot of progress in lens design in the last 10 years. Some lenses are still designed by an old buy who remembers Zernike polynomials and does his work with a pencil and paper. You don’t want these. Get a modern lens design known as digital progressive lenses, high definition, HD, or more commonly, free-form. These designs are made using a computer and divide the lens up into “pixels” where a performance goal is met subject to an overall cost function. The in-between-points are probably interpolated with a cubic spline. You see, the problem with lens design is, if you try to make it better in one place, it gets worse in another place. This is why it is an interesting design problem. The modern, free-form designs are _far_ better than the old designs. Some designs actually allow precise measurments to be made on your frame _before_ the lens is made; this information is sent to the lab and incorporated into the lens design, essentially a custom-made design. Shamir comes to mind, but there are others. At least one company has a slick jig for an iPad and an optical splitter that fits over the iPad’s camera so that even a monkey could set this up without screwing things up. (FYI, be prepared to deal with monkeys.) The free-form designs can trade off near, intermediate, and distance regions that you can select depending on your lifestyle. Many new free-form designs excel at getting a wide channel, which is to say, the intermediate, which is great for most computer work. Free-form designs are much better at getting the near vision wider. My current lens is a free-form design and it is _far_ better in both intermediate width and near width than my old conventionally designed lenses. (FWIW, my current lens is the best Seiko lens, and I recommend them.) And you will also find that there are “computer glasses” which you should consider; these have giant intermediate and near regions and pretty much punt on distance.
Many dispensers will bitch and moan if you get a short lens (frame); these became fashionable 10+ years ago and still are. That’s bullshit. They will try to put you in an “old fart” frame because they claim that it forces fewer compromises on the design. Then they will take your prescription and increase it so that it is more powerful at the bottom of the giant lens so that it is correct at the near vision region that you actually use. You simply can’t rotate your eyeballs far enough to see to the bottom edge of a giant lens.
Getting the frame adjusted (bent) is critical for progressives. The optical axis has to be aligned with the optical axis of your eyeballs. The lenses come from the lab with a fitting cross or dot on the lens. If you get your new lenses and do not see the fitting cross, your dispenser has removed it. Ask them to put it back on. They have a simple tool to do this. The fitting cross should be directly in front of your pupil when holding your head normally and looking at a distance. You won’t be able to see the cross yourself but they can; or you can look in a mirror to satisfy yourself that it is correct. THIS IS IMPORTANT! The nose pads can be adjusted to raise or lower the fitting cross. Two other parameters are important: the pantoscopic angle and the wrap angle. The pantoscopic angle is the angle that the mostly vertical lens makes with the front of your mostly vertical face—look at your profile using a double mirror. Most designs are intended for about 10 degrees. This is a little hard to measure yourself but you can eyeball 10 degrees. Your dispenser should bend the frame for you; in my case, I had to learn how to do this myself. Obviously if you have plastic frames this isn’t always an option, so word of advice: get metal frames. Best, get three-piece frames. The wrap angle is how much the frames wrap around your head. Imagine looking at your head from above and observing how they seem to wrap around, or match your head shape. Getting this set as much as you or your frames can tolerate will enormously help the global distortion (not focus) that you see. Demand that this be be adjusted or do it yourself. (Bending metal frames is not rocket engineering. Get some needle nose pliers and pad it with a thick wash cloth to avoid marring the frames. I have titanium frames—Marchon 720—and they are great to work with and indestructible.) Overall, get the frames as close to your eye as possible, as this also reduces global distortion. (Contacts are zero distance and have zero global distortion.) I set mine so that my eyelashes gently brush the lens when I’m laying on my back, face up.
Pay for optical obsorbing coating. This is a worthwhile add-on, as it greatly reduces all sorts of anamolous reflections. This is kind of cool—it is seven or nine layers of optical material of slightly different index of refraction, sputtered on the lens in a series of quarter-wavelength absorbers. Pretty neat, and really effective. And if you get rimless or monofilament-attached lenses, don’t get the edges of the lenses polished—polished edges reflect overhead lights and sunlight like crazy and you will see these annoying reflections all the time in such lighting. Get the dull finish. The dispenser will try to tell you that the polished edges is cosmetically better but screw that. I have pretty thick lenses and nobody has ever said my unpolished edges look uncool.
The vast majority of material used for lenses is polycarbonate. This is the hard, tough plastic that Compact Disks are made of. That’s fine if the only thing you’re going to shine through them is a laser (single wavelength) but for the octave or so of visible light, polycarbonate is the _worst_ material there is. Why? Because is it seriously dispersive. That means that the speed of light (and the index of refraction) is dependent on the wavelength of the light. And polycarbonate is the worst. Really. There is a crude but common and effective measure for this phenomonem called the Abbe number. Polycarb’s Abbe number is 30. A resin known as CR39 is outstanding with an Abbe number of 60, which I think is also the Abbe number of crown glass. The so-called high-index materials are pushed by many dispensers. They tend to have also crappy Abbe numbers and are not nearly as strong as polycarbonate but they are popular because the lens can be made very slightly thinner. So if you don’t care if you go blind when your car’s airbag goes off in your face, get a high-index lens. Otherwise, there is a good compromise: Trivex. Some manufacturers re-name it, but it’s still Trivex. It is as tough as polycarbonate but has has intermediate Abbe number of 45. I forgot to mention why dispersive materials are bad—they act like prisms for anything off the optical axis, and the further off, the worse. I mean, they separate colors into their spectral components. Not cool. This will bother you especially in high contrast scenes such as nighttime signs or reading in bright light. You will actually see the color fringing. Just get Trivex and be done with it.
You declared your use very clearly. Your choices are progressive including “computer glasses", lined bifocal including so-called executive or Franklin bifocal which extends the “line” across the entire width of the lens which I think you should seriously consider, or a single-vision lens that you wear only for computer work, but if you need correction for computer work then you also need it for reading and other close stuff. Your choice depends on if you are OK with removing and replacing your glasses during the day and carrying them to restaurants etc. versus how you tolerate multifocal, progressive or conventional. But—a single-vision lens will work just fine for your use (but your dispenser won’t make as much money off of you). And you should know that adapting to progressives can take a while. Give it at least three weeks. You will be surprised what your brain can adapt to especially if you have never worn glasses before. But seriously, a free-form design will be easier to adapt to compared to an old-school progressive design.
Oh yes—you will not find _anyone_ who is an expert on comparing all of the available designs, but some dispensers are more concerned about learning this information than others. I don’t know how you find them. I found tons of useful information on the discussion lists at optiboard.com.
So there. I believe I started out saying that I would be brief. :-/
