A Little Explanation on Progressive Lenses

There is a common misconception amongst patients which I’ve come across many many times.

The vast majority of patients are under the impression that there is only one progressive lens.  This has been in great part due to a failure amongst all eye care professionals to explain the choices for fit.  At this time there are several hundred progressive lenses.  There are laser etchings on the lenses which help the eye care professional to identify which of the several hundred lens designs you are currently wearing.

LensMarkings.png

All progressive lenses are not created equal.  The example I like to use with my patients, is that saying ‘progressive’ is like saying ‘car.’  There are different manufacturers (i.e. Toyota, BMW, Ford, etc.).  And each manufacturer has several models, each designed to suit a different budget, or function (i.e. Prius, Camry, Highlander).  One of the most critical jobs for an optician is to have the conversation with the patient to help identify which progressive lens is best suited to the patient’s needs.

Be Careful when Price Shopping

This diverse market of lens options can make price shopping for progressives very challenging.  Understand that not all shops and locations even offer all the options available.  Most offices work most closely with one manufacturer or another.  For example, some “big box” retailers will only work with one design, and it’s a much older technology with the necessary pitfalls associated with less advanced manufacturing.

How Progressives Work

PALChannel.png

A progressive lens was developed to eliminate the hard “line” of a traditional bifocal, as well as to provide a large, comfortable intermediate vision zone.  Essentially, in a progressive lens, you can see clearly and in focus through a distinct “hourglass” channel.  Outside of this hourglass, generally in the lower periphery of the lens, vision is not as clear.

I find the best way to describe this for the layperson to understand, is to imagine a bifocal lens made out of clay.  If you wanted to eliminate the physical “lip” of the reading zone, you would put your thumbs down into the middle of the lens and “squeeze” the clay out towards the periphery to smooth out that lip.  In essence, this is what is happening with a progressive lens.  This means instead of having a blurry line in the middle of your vision, your have a blurry edge to the lens.  There are various different lens technologies amongst the larger family of progressive lenses to try and handle these inherent issues for no-line lenses.

A Word on the Technologies

OK, I’m just going to be straight up here.  Some of the technologies involved in manufacturing progressive lenses (or PALs in the parlance of the industry) are not easy to explain in layman’s terms.  To put it as simply as possible, older lens tech used to generate PALs involves molding the prescription into the backside of the lens only.  This is a less expensive method, and has the drawbacks you might suspect.  When you put all the power on one side of the lens, it means the “channel” for your best vision is necessarily smaller than when the power is shared across the front and the back of the lens.

Newer lens technologies digitally surface the power (using lasers to cut lens) on both the front and the back of the lens.  When the power is “shared” across the front and the back of the lens, it opens the channel of your vision up.  Giving more space for clear focus, and pushing the “distortion” further off to the sides, and out of your field of view.

PALSwim.png

In addition, digitally surfaced lenses address the problem of the “blurry” periphery in a very different way as well.  The periphery in a PAL is blurry because it is actually unwanted astigmatism correction.  Astigmatism is correction that has not just power, but also angle.  In an older “analog” lens design that angle of the astigmatism is constantly shifting, which can create a sensation of “swim.”  Essentially, when you move your eyes around, you can feel like you’re riding on an ocean wave.  When a lens is surfaced digitally that unwanted astigmatism is all placed along a similar angle, or axis, so you don’t notice the “swim” as much and they are more comfortable for long term wear.

Take Away

Realize, that when your optician spends a fair bit of time explaining or discussing progressive lenses, it’s not because we’re going for a hard sell.  This is an advanced lens technology which takes time to accurately measure and fit.

If you have questions, you don’t feel were adequately explained here, please feel free to contact me.  Send an audio clip via email and I’ll answer them on my upcoming podcast.

One thought on “A Little Explanation on Progressive Lenses

  1. Pingback: Vision Insurance vs. Medical Insurance | The Eyes Have it

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