Progressive lenses allow you to see at all distances with one pair of glasses. They have your distance prescription (if you need one) in the upper half of the lens and increase reading support as you move your eyes toward the lower half of the lenses. You simply move your head and eye positions to allow you to focus through different areas of the lens.
This lens design has a smooth transtion from distance vision to the reading power. No visible line is required to built the different lens powers into one pair of glasses. Those achivements by the manufacturers of progressive lenses work when three things get combined on one lens surface.
- radii that produces the lens power for distance vision
- radii that produces the lens power for the reading distance
- radii that blends the upper two together to cover the difference
The blending process to cover the differences in the lens leads to blurry fields in the periphery where the blend is located. One easy rude says:
The higher the difference between the lens power for distance vision and the lens power for reading the more blurry it gets in the periphery. You can understand easily how progressive lenses work by having a look at the illustration below.
Here in the first picture below you can see two different lens powers are combined in one lens design. But the difference to a modern progressive lens is you can see a ledge or a visible line on such a lens design.
So in the next step, in theory, is to cut out the marked areas of the lens design in order to get rid of the ledge and to smooth out the lens surface. the concept here is just about how they work and why they are blurry on the sides. If you want to get more detailed information about the grinding technique visit our article on how progressive lenses are made.
What gets added in this step is an area that has not the lens power needed for your distance vision nor the reading distance. The purpose of this area is solely in smoothening out the different shapes between the lens powers. If you look through the grey areas you will experience blurry vision.
Here in this picture we have a pretty wide field of view when it comes to the distance segment and the reading segment. But as you can imagine the field of you in progressive lenses is highly dependent on the difference in radii in the upper half and the lower half of the lens design.
If you have a big difference which is an ADD value of 2D the field of view will be much narrower for you. Because the grey areas get bigger because they need to cover a bigger difference in needed lens shapes.
In the pictures above all you had in the lens were two different lens powers. A progressive lens design works by providing you a smooth transition form far to near vision. That is why in the last step we added a mid distance section which leads to a change in lens power with a smooth transition from the upper half to the lower half of the lens.
How do progressive lenses work for reading?
Progressive lenses work for reading if you are willing to point your nose into the direction you want to see clear in. The reason is a progressive lens only gives you a small field for reading. If you perform eye movements to the sides without pointing your nose into the same direction you will see the text you want to read blurrier.
This works in most cases for half an hour but if you want to really dive into a book for a longer time you will almost certainly enjoy your book more with reading glasses. Because they provide you with a clear field of view that is multiple times as wide as with a progressive lens. This is why progressive lenses do not work best when it comes to long reading sessions.
This experience also changes with the amount of reading power you need. The higher the reading power has to be the narrower your field of view becomes. This is true for every progressive lens design on the market. No matter the manufacturer.
If you want to know more about what kind of width in the clear field of view to expect from your progressive lenses read this article here about how wide your field of view will be in your progressive lenses.
If you had a closer look on the picture above you can see the grey areas increasing as the Add value goes up. This is the reading power I was writing about earlier. Usually when you start out in your 40s the reading support has to be lower and the field of view is wider. In such a case progressive lenses can work just fine for you.
Even in longer reading sessions. Because you are way less restricted to someone in their 60s who needs a higher Add value. In such a case reading glasses or computer glasses in addition to progressive glasses is a very good option to have.
For whom Progressive lenses do not work
When movements in head, neck and soulders are heavily restricted
Progressive lenses do not work for people that are heavily restricted in their ability to point your head into a certain direction they want to see clear in. Those limitations can have several backgrounds but when movements are limited it is harder to get progressive lenses to work correctly.
When the difference in lens power is higher than 1.5D
When you look through your progressive lenses you are forced to move your eyes to different spots. Only this way you can use different lens powers and the smooth transition of a progressive lens between those lens powers. But if one eye needs a stronger lens than the other the picture gets deviated.
And more so for one eye more compared to the other. In the picture above you can see the pen’s picture is deviated down on the right compared to the left. Your eyes can not compensate for those changes well. They are called prismatic effects. Every lens has them. But if lens powers are very different this can lead to headaches or double vision.
Fluctuations in Refractions
In some cases buyers of progressive glasses are very dissatisfied with their purchase. Because they can not adapt to the lenses. One possible reason could be a fluctuation in the refraction gaining on.
You need to understand that the prescription of lens power you get is a result on what you needed to see clear in the time you were in the optical. But for some people this lens power changes day by day or even during hours.
The reason for this changes in needed lens power is very diverse and should be checked by your ophthalmologist and your general practitioner too. When three appointments were made and every time you went into the shop another lens power was measured the changes come stem from:
- Your eyes due to a change in corneal shape
- Thyroid gland
- Dry eyes
- Changes in your blood pressure
- Hormonal changes you are going through
All those factors can play a role here. In some cases the reason can be identified very quickly in some cases not. But changes in refraction makes it very hard to get used to progressive lenses. In most cases they will not work for you in such a case.
Of course, this depends on how big those fluctuations are. Opticians and optometrists are performing different tests to have reference values if you visit them a second or third time to check for fluctuations.
But you have fluctuations I highly recommend you see the medical doctors first to go through the mentioned points before you get your progressive glasses made.
I hope you enjoyed this article about when progressive lenses work and how.
I wish you a great day.