So you have astigmatism? You are not alone. In fact, there are millions just like you. And eventually, those millions will develop cataracts and need cataract surgery. Fear not, though, astigmatism can be corrected with cataract surgery - and corrected quite well.
If you have high amounts of astigmatism, the best cataract surgery for astigmatism involves special lenses called toric lenses to eliminate the astigmatism. For smaller amounts, a special technique called limbal relaxing incisions are used to correct the astigmatism.
But unless you work in the eye field, words like toric and limbal probably sound foreign. So let’s go over what is astigmatism and how cataract surgery can correct it.
What is astigmatism?
This is a football; Photo by Dave Adamson on Unsplash
The easiest way to understand astigmatism is that the cornea is shaped more like a football than a basketball. What does this do? This blurs and distorts your vision. Fortunately ordinary astigmatism does this is a very regular way. This allows astigmatism to be corrected with glasses.
If you’ve ever taken a look at your glasses prescription, it contains three different numbers per eye (unless you are one of the few people with absolutely zero astigmatism; then it contains only one number per eye). The last two numbers in the prescription are measurements of the astigmatism in your eye.
The higher the middle number (measured in something called a diopter, the optical unit of measurement), the higher amount of astigmatism you have. This ranges from less than 2.0 to up to 6.0 in extreme cases.
The last number simply measures the direction of where the astigmatism is pointing. If you lay a football down on the ground, the long axis of the football can point in any direction. Same thing with astigmatism; so this direction gets measured so that it can be corrected.
Let’s head to cataract surgery
Unrelated to astigmatism is cataracts.
Cataracts are a clouding of the natural lens inside the eye. Cataracts happen to everyone; it’s just a matter of when. Some people get cataracts at a young age, others don’t have to worry about cataracts until well into their senior years.
See also Your Comprehensive Handbook To Learn What Are Cataracts
But regardless of when cataracts develop, cataracts can be treated easily enough with cataract surgery. During cataract surgery, the cataract is removed and replaced with a new clear artificial lens.
This new artificial lens is a large key to getting the best vision after cataract surgery. This is especially the case if there is astigmatism.
But not all artificial lenses are the same! A typical cataract surgery uses a basic artificial lens. This lens is clear and able to eliminate some glasses but it can’t do everything. This basic lens is unable to correct astigmatism. If you have large amounts of astigmatism before cataract surgery, you will still have large amounts of astigmatism after cataract surgery and will need glasses.
Toric lenses to correct astigmatism
Not everyone likes glasses and so upgraded artificial lenses were developed. These upgraded lenses were designed to be able to correct astigmatism during cataract surgery - the toric lens was developed.
The word toric simply means that the lens is able to correct astigmatism. These lenses come in a large range of powers in order to match the power of astigmatism that you have in your eye. Toric lenses can correct from 1.0 diopter of astigmatism to a little over 4.0 diopters. That large ranges covers almost everyone and provides a very individualized correction.
But wait, isn’t there another number that must be corrected with astigmatism? Yes! Good memory. It’s the direction. You can’t just simply place this lens within the eye and expect it work. It must correct the astigmatism in the appropriate direction.
Toric cataract lens; image © 2018 Jung, N.Y., Lim, D.H., Hwang, S.S. et al., used under CC BY 4.0 / modified from original
If you look closely at the toric lens above, you will notice that there are two different lines of dots on the lens. These line marks indicate the direction of the astigmatism correction. Once the lens is placed within the eye, the lens is simply rotated until those lines line up with the direction of the astigmatism on the cornea. Once the lens is in place and healed up, it stays in that direction to continue correcting the astigmatism.
Toric lenses are a very elegant way to correct astigmatism at the time of cataract surgery. But what if your astigmatism isn’t bad enough for a toric lens?
Limbal relaxing incisions can correct small amounts of astigmatism
For smaller amounts of astigmatism, toric lenses are too powerful. Something else needs to be done to get rid of the astigmatism. The technique to correct smaller amounts of astigmatism is called limbal relaxing incisions or LRIs.
Think back to the football: one side of the football is much steeper than the other side. If you take out a tape measurer, you will find that the circumference of the steep side is less than the circumference of the flatter side (if they both had the same circumference, we would be talking about a basketball). If we could somehow relax the steep side and increase its circumference, we could turn the football more into a basketball. That’s the goal behind limbal relaxing incisions.
By placing a tiny incision against the steep part of the cornea, the surgeon can relax that steep part of the cornea and flatten it - reducing astigmatism.
Back in the day, limbal relaxing incisions were performed by hand. But nowadays, LRIs are more commonly performed by a laser at the time of cataract surgery. While limbal relaxing incisions by hand weren’t bad, the advancements of lasers has made these corrections more precise and accurate.
Limbal relaxing incisions are great for astigmatism 1.0 diopters or less (coincidentally the same range that toric lenses don’t work for). As you get above 1.0 power, limbal relaxing incisions get less accurate and toric lenses become the more optimal way to correct astigmatism.
Summary
If you need cataract surgery and have astigmatism, you are in luck. There are great ways to correct astigmatism with cataract surgery. Using either a toric lens or limbal relaxing incisions (depending on how much astigmatism you have) provides the best cataract surgery for astigmatism.
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