Progressive Addition Lenses (PALs or Progressives) are both a blessing and a curse. For those of us in our mid-40s and beyond, they are the best and most natural way to achieve clear vision at all distances. The negative of progressive lenses is that by their very nature, they only have limited areas on the lens that are useful for a given working distance. In some cases the area of clear vision for a particular task simply may not be great enough. We see this most commonly in people who spend a lot of time on a computer.
Progressive lenses work by gradually blending focusing power from the distance zone at the top of the lens, to the reading power at the bottom of the lens. An inevitable consequence of this is that some unwanted distortions are produced in the lens periphery. ALL progressive lenses will have some of this distortion. It's impossible to produce a completely distortion-free progressive lens.
Having said this, progressive lens design and production methods have improved hugely over the past few years. Computerised modelling and digital freeform manufacture allow incredibly precise curves to be generated on the lens surface. This advance in technology has meant that the discomfort and blur of peripheral distortion is greatly reduced with modern progressive lenses from the leading ophthalmic lens companies. At Cassidy Eyecare, our non-adapt rate to progressive lenses is less than 5%.
The simulation below contrasts the difference between the view seen with an older-style progressive and a newer digital design. While it is typically exaggerated, it does illustrate the point.
One thing to note is that even with the improved modern lens design, the area of clear vision at a computer distance is still restricted. For many people, that doesn't cause a problem. In others, it does. In those cases, a more specialised pair of glasses designed specifically for computer and/or near work may be required.
If you think about it, that makes sense. Few people would expect a single pair of shoes to be perfect for all occasions. If you're a runner, you need shoes specifically designed for running, which probably won't be the same pair you'd wear to a fancy restaurant. The same principle applies to spectacles: a good general-purpose design probably won't be as good for a particular task as a more specialised lens designed specifically for that task.
If you are having problems with your progressives, the things to consider are:
- Has a good and appropriate design of PAL been used?
- Is a single pair of glasses adequate for all your vision needs?
- Is your frame fitting well, and have the lenses been accurately positioned in the frame?
We have touched on the the first two factors in this article. The importance of frame fitting and accurate dispensing measurements for PALs will be covered in a later piece. As usual, if you have any questions regarding the information in this blog, feel free to flick an email to us through our Contact Us page.