Toric lens vs. future astigmatism

When I researched this I came across one study that indicated that both oblique and with-the-rule (WTR) astigmatism remains stable following cataract surgery and that against-the-rule (ATR) astigmatism tended to slowly migrate in the direction of becoming WTR astigmatism. The followup period in the study was 8 years. The progression rate and impact of ATR toward WTR was not enough to dissuade me from getting toric lenses. Two surgeons assured me that any future changes in astigmatism would be correctable with glasses. It's a similar situation with the natural eye in that it can have both corneal astigmatism and lenticular (lens) astigmatism and that is commonly corrected with glasses.

"Long-term outcomes of cataract surgery with toric intraocular lens implantation by the type of preoperative astigmatism" on Pubmed.

The first thing you need to do is find out from your surgeon what your expected astigmatism will be after surgery. It is not the same as your eyeglass prescription. It most likely will be less. But if it is in the 0.75 to 1.0 range, that would take the minimum power toric. If your interest is in eyeglass free vision I would go for the toric. Most of the change over time seems to be in the lens, not the cornea, so I think it makes sense to do the correction. I didn't do it, and now I regret not going for a toric.

With that small amount of astigmatism, your cataract surgeon could treat it with limbal relaxing incisions, and save you about $2,000. Or don't do anything and wear eyeglasses to correct. In my case, I had a lot of astigmatism--2 diopeters per pre-surgical measurements. I didn't want a toric IOL and thought I would need eyeglasses, but at my surgeon's suggestion, she set Intermediate vision as the refractive target, and I can see quite well without eyeglasses. I only need readers for small print. That was my personal experience with cataract surgery.

Like Lynda, I had my astigmatism corrected with limbal relaxing incisions (LRIs.) Like Ron said, your corneal astigmatism might be different than your eyeglass prescription which corrects for both the astigmatism in the natural lens and the cornea. If your corneal astigmatism is less than -1D, it should be easily correctable with LRIs. Research that I've seen shows that corneal astigmatism can be consistently reduced by 50-60% with LRIs, if you are a candidate and your surgeon is comfortable performing them. After surgery, if your astigmatism is below -0.5D, you probably won't notice it.

In my case, my right eye was on the border of what the surgeon thought would be correctable with LRIs, a bit more than -1D. Ten weeks after surgery, I have no measurable astigmatism in that eye. My left eye had corneal astigmatism of -1.4D and the surgeon recommended a toric. I rejected it in favor of the LRIs. As expected, four weeks after surgery, my left eye prescription measured -0.5D cylinder, enough that I can notice ghost images when looking at far away lighted signs at night or the moon out of just the left eye. In good light, I don't notice ghosted images out of the left eye. With both eyes, I don't see ghosted images.

My logic for rejecting the toric: It added complexity and additional long-term risks while adding minimal benefits. I had/have typical, easily correctable astigmatism and wouldn't have minded wearing glasses after surgery since I've been myopic my entire life. Turns out, I don't really need glasses except perhaps +1D readers for low light near vision (that I've not yet purchased.)

I wasn't convinced that corneal astigmatism would be stable over the 20-30 years that I hope to use the IOL. I know that my astigmatism, both axis and cylinder, had changed substantially over my lifetime but I don't know if that was the lens changing or the cornea but I suspect both.

If the toric IOL axis is off by just 3 degrees, the residual cylinder will be 10.5%, and if off by 30 degrees, the lens will have be completely ineffective. There are several ways this could happen:

1. the eye biometry is off, possibly due to additional pressure on one side of the eye
2. the IOL manufacturing isn't quite accurate
3. the IOL is installed at the wrong angle
4. the angle changes slightly as the incision and capsular bag adheres to the new lens.
5. the corneal astigmatism changes over time.

Additionally, astigmatism is generally undercorrected . This avoids problems with "flipping" the astigmatism which can cause the brain to have difficulty processing the image. I figured the chances of getting a better long-term outcome with a toric rather than LRIs was minimal and were far outweighed by the risks of having to reset a mis-aligned toric at some point in the future. Short-term, I'd guess the toric might have been better to correct the -1.4D in my left eye if all went well but the long-term risks seemed to high for me. I'm happy with the LRIs even though I have -0.5D of residual astigmatism in one eye. Many who get torics don't do much better than that.

If you have corneal astigmatism of less than -1D, I doubt many surgeons will use a toric, especially if they are comfortable with LRIs. Between -1D and -1.5D, you'll get differing opinions about what to do. More than -1.5D and most will recommend torics since LRIs would likely leave you with at least -0.75D of residual astigmatism and it would give you noticeably blurry uncorrected vision most of the time.

In the US, torics and LRIs are considered cosmetic. Torics are a bit more profitable than LRIs for surgeons and far more profitable for IOL manufacturers. They have substantial monetary incentives to recommend torics in marginal cases where the patient benefits are minimal.

Some additional comments:

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While I think it is less likely once the natural lens is gone, changes could still occur in your corneal astigmatism over time. But, you will have to deal with them, or not, regardless. If you start with the lowest possible astigmatism post surgery, you will have more room for deterioration before you are forced to eyeglasses for astigmatism correction. Remember these are only issues if you want to be eyeglass free. If you plan to wear glasses there really is no point in getting a toric IOL. Eyeglasses easily correct astigmatism.

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To my knowledge it is no harder to correct astigmatism in someone who has a toric IOL than it is in someone with a standard lens with corneal astigmatism. You do not paint yourself into a corner with a toric lens.

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In Canada where I am, you pay for a premium lens based on the differential between it and a standard lens. A toric is considered a premium lens and costs $1,100 more that the basic lens which we get for free. I assume part of that is to cover the higher cost of the lens, and part goes to the surgeon. Additional measurements are required to determine how much power and at what angle to place the lens. And, when it comes time to implant it, they have an additional step to mark the eye, and then position it after insertion. They also take the risk that it might move post surgery and they have to reposition it.

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My surgeon refused to do LRI. He said he used to do it, but stopped because he could not get reliable enough outcomes to meet his expectations. He said he would refer me to someone else, but he would not do it. I took it to mean that he did not want to deal with the potential negative outcomes of LRI surprises.

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I went into my surgery with a non toric thinking that if things did not turn out well, all I had to do was get Lasik or PRK. My surgeon even told me that was an option. It turned out to not be true in my case. When you do astigmatism reduction with laser your lose the negative sphere add that astigmatism provides. And, the killer is that you cannot add more negative sphere (myopia) with laser. They can easily reduce myopia (make the cornea less steep), but they cannot easily make the cornea more steep, or increase myopia.

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If I had it to do all over again I would have gotten a toric lens. I ended up painting myself into a corner that I cannot get out of short of doing a lens exchange to a toric. The good news is that I have -0.75 D astigmatism in my close eye with monovision, and my vision is still pretty good. I am eyeglasses free, but I know now it could have been better if I had gotten a toric. I have a drop shadow on letters when reading, and especially when it is white text on a black background (like on my iPhone). I can still read, but it slows me down. I think I would have largely avoided that with a toric. I have progressive glasses with astigmatism correction. When I wear them (which is almost never), the drop shadow pretty much goes away.

Greg59 really summed up all my concerns with the toric... risk vs. benefit. i do wish the surgeons weren't incentivised to use toric as you don't know if it's really in your best interest or theirs!

I'm glad RonAKA weighed in again because that does balance my thinking a bit.

I have a consult with my surgeon this week to go over my biometrics and make a final decision so i really appreciate the details everyone has shared here.

One more bit of information to consider. I have two years experience with the first eye to have cataract surgery. The cylinder in the eye varied from -1.25 to -1.5 to -2.75 in the five years prior to surgery. I'm sure the jump to -2.75 was due to the cataract which was diagnosed at that time. I made a special visit to the optometrist because I noticed double vision. The cylinder in the three years since surgery with a non toric have been:

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Year: Sphere, Cylinder

2020: 0.00, -0.75 @ 80 deg

2021: 0.00, -0.75 @ 80 deg

2022: 0.00, -0.50 @ 83 deg

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While not a long term outcome, it certainly looks quite stable for now. If anything astigmatism is improving. I did not consider a toric in this eye as the surgeon was expecting cylinder to be between 0.00 and -0.40 D. It turned out to be a little higher than that....

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In any case I think this indicates that much of the change we experience in vision over time may be due to changes in the lens, and less so on changes in the cornea. This bodes well for stability in vision post cataract surgery.

Another option to consider is the IC-8 lens (not available in all countries but has long been available in Europe and Australia and will be rolled out in US in first quarter of 2023). It corrects up to 1.5 D of astigmatism and has no axis. If your astigmatism changes over time, or if the lens rotates, it does not matter, as long as your astigmatism stays under 1.5 d.