Looking to get out of glasses? Then you’ll also need to look into having all your astigmatism corrected during cataract surgery. Having astigmatism will make your vision blurry.
Fortunately, there is a pretty easy way to do this: the use of cataract lenses for astigmatism - called toric lenses.
These lenses work very well to eliminate astigmatism and you can’t really go wrong with just going with any of the different toric lenses on the market. But since all want the best, let’s look at how some lenses perform just a little bit better than the others.
In particular, toric lenses made by the manufacturing company Alcon tend to be a little more stable to correct astigmatism just a little bit better.
Let’s see how.
How Lenses Correct Astigmatism
If you take a look at any lens (such as a camera or telescope lens), it looks like a sphere. As a result, these lenses are called spherical lenses; easy enough. If we divide those lenses up into slices like a pizza, each slice is going to be exactly the same in how it focuses light.
Astigmatism is different. Not every slice of the pizza is going to be the same.
With astigmatism, one direction (called axis) of the cornea is steeper than the other. Because of this, vision passing through that axis will focus at a different spot than vision passing through the flatter axis.
How astigmatism causes vision to be out of focus; image by Sebastian Kosch (Ginger Penguin, CC BY-SA 3.0, via Wikimedia Commons / modified from original
However, while not all the slices of pizza are going to be the same, you will notice that slices directly opposite of each other will be the same. This is because while astigmatism isn’t infinitely symmetric like a sphere, it does have some symmetry. Rotating the cornea 180 degrees will allow everything to match up.
So to correct the astigmatism, we just need to line up a lens which equalizes the steeper part of the cornea to the flatter part of the cornea - negating the astigmatism. And that’s how all lenses correct astigmatism.
During cataract surgery
Things don’t change much during cataract surgery. The principle is still the same. A lens is created which has the ability to focus light from the steep part of the cornea at the same spot as light from the flat part of the cornea (compensating for the power of the astigmatism).
This lens is then aligned in the direction of the astigmatism where the cornea is the steepest.
But here’s the one key difference. When astigmatism is corrected with glasses, the lens is specifically made so that the astigmatism lens corrects the proper direction when the glasses are sitting on your ears and nose. But with cataract surgery, these lenses instead are made for all directions instead of a specific direction.
How is that done you may say?
Once the cataract is removed and the new artificial toric lens is placed, it is then rotated to match up exactly with the astigmatism. Anywhere between 0 and 180 degrees (remember that astigmatism is rotationally symmetric 180 degrees apart).
The lens eliminates astigmatism and we can see perfect. And all is well with the world. Right?
Issues With Rotation
The ability of cataract lenses to correct astigmatism with ease by just rotating the lens in the proper location gives us great power to correct vision.
But there is one drawback: the lens can rotate out of position as well.
Astigmatism correction works best when the toric cataract lens is aligned perfectly on the axis of the astigmatism. If the lens rotates out of position, the lens becomes less effective. For every 10 degrees of rotation, the lens becomes 30% less effective. This means left-over astigmatism after cataract surgery. The more astigmatism that needs to be corrected, the bigger the issue.
This is one of the problems with toric lenses.
Fortunately, this can be fixed; but with another small operation. The surgeon rotates the toric lens back into the proper orientation. Also fortunately, this operation is only needed in a small number of cases, around 2% of the time after cataract surgery with toric lenses.
But preventing the lens from rotating as much as possible is ideal. And this is what distinguishes different cataract lenses for astigmatism.
The Optimal Toric Lens
Within the United States, there are three major toric lenses on the market.
- Clareon by Alcon
- Tecnis by Johnson & Johnson
- Envista by Bausch + Lomb
If you desire a more advanced lens to also get out of reading glasses, those also come in toric versions based upon similar technology. (For instance, Alcon’s Panoptix is based upon the Clareon model and Johnson & Johnson’s Synergy is based upon the Tecnis design).
In general, these lenses are pretty similar. These lenses are all designed to give great vision. But there are a few key differences such as how optimized the lens is for night driving or how the eye appears with the lens in place.
Rotational stability of the lens is another key difference. Because of differences in the shapes and materials of the different lenses, some lenses are more prone to rotate out of position than others.
Fortunately, we have large studies that have examined just this particular issue.
Of those three lenses above, Alcon’s lens comes out ahead with the least chance of rotating. The Envista and the Tecnis are almost twice as likely to rotate compared to Alcon’s lens.
Note: The above studies were performed with Alcon’s previous generation of lens called Acrysof. While direct head to head comparisons aren’t yet available with Alcon’s current generation, Clareon, the initial results of this lens have it looking as good or even better than the previous generation on staying in the right orientation.
Summary
A problem with toric cataract lenses for astigmatism is that they can rotate out of position. If the lens rotates too much, this can reduce the effectiveness of the correction and leave one with residual astigmatism after cataract surgery. While all the different toric lenses are similar, Alcon’s lens shows the best results as resisting unwanted rotation after cataract surgery and this lens can be considered the best cataract lens for astigmatism.
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