Cataract Surgery After Radial Keratotomy: What to Expect

If you had radial keratotomy back in the 80s or 90s, you’re getting to the age where cataracts turn up, and somebody has probably already told you that your cataract surgery is going to be complicated. I wouldn’t put it that way. The operation is the same one everyone else has. What’s different is the cornea you’re bringing to it, and that changes how I plan things, which lens I’ll offer you, and how long it takes to know the result. Those are the things I want to walk you through here.

What RK did to your cornea

RK corrected short-sightedness by making a set of deep cuts into the cornea, spreading out from the centre like the spokes of a wheel, so the middle of the cornea flattened. It did work, and for a while it was the most common refractive operation in the world. LASIK took over, and a big part of the reason was what those cuts do over the years.

They never really heal. Every one of them stays a line of weakness, and a cornea with four, eight or sixteen of them is never quite structurally sound again. It keeps flattening slowly, for decades, which is why most RK eyes drift long-sighted with time. It also changes shape over the course of a day, so a lot of my RK patients tell me their vision is better in the morning than by the evening. And it’s often irregular, so the light doesn’t come to one clean focus whatever glasses you wear.

While nothing else is going on, the eye copes with all this. Cataract surgery stirs it up.

Why your vision will fluctuate, sometimes for six months

Any surgery on the eye makes those old cuts swell. When they swell they widen, the cornea flattens, and you become long-sighted for a while. Over the following weeks the swelling goes down, the cornea steepens back up, and the prescription drifts back the other way. The usual advice is to wait a minimum of three months before you judge the result or get glasses made. I’d go further than that. In my experience it’s very common for the vision to keep moving for up to six months, and the more cuts you have, the longer it goes on and the bigger the swing.

I tell people this before surgery because otherwise the first couple of months are alarming. If your vision is blurry, or long-sighted, or different in the afternoon from the morning, that’s the cornea settling down, and it’s what I’d expect. I won’t finalise your glasses in that period, and I won’t make any decision about fine-tuning the result, until I can see the cornea has stopped moving.

Working out the lens power

With every cataract operation I have to choose the power of the lens that replaces your cloudy one, and that calculation starts from measurements of your cornea. RK corneas mislead those measurements. The flattened central zone is small and irregular, most instruments read its power as higher than it really is, and if you plug those numbers into a standard formula you end up long-sighted.

So I use the formulas designed for post-RK eyes, the Barrett True-K and the ASCRS calculator mostly. Even so, the chance of ending up with some refractive error is higher than in an ordinary eye, and I’d rather you heard that from me now than found it out later. I also aim a little short-sighted on purpose. An RK cornea keeps flattening for years, so a result that’s spot on today will have drifted long-sighted in ten years’ time, and I’d rather build in some room for that.

If you do end up with a significant error once everything has settled, I’m reluctant to do laser on a cornea that’s full of incisions. The better option in these eyes is usually a secondary lens, which sits in front of the first one and can be changed or taken out if it needs to be.

Which lens? It depends on how many cuts you have

This is the question I get asked most, and my answer really does depend on the number of incisions.

If you have four cuts and a reasonably regular cornea, a multifocal or extended depth of focus lens is still on the table, and some people do well with them. There’s a published series of 24 post-RK eyes with an EDOF lens where 78% of patients were happy with the result, and uncorrected vision went from about 6/22 to 6/10. But there are two things I’d want you to understand properly first. One is the quality of the vision. These lenses split or stretch light to give you a range of focus, and an RK cornea scatters light on top of that, so a proportion of patients find the picture hazy or washed out in a way they wouldn’t with a standard lens. The other is the higher chance of the power being off, which matters more with a lens that relies on the focus being exact. If you decide to go ahead with one, you do it knowing those risks, and knowing that a lens exchange is there if it doesn’t work out.

If you have more than four cuts, so eight or sixteen, the cornea is more unstable and more irregular, and I generally steer people away from multifocal and EDOF lenses. The optics just aren’t good enough to carry them, and the drift afterwards is bigger. A good monofocal lens, aimed carefully, is the choice I’d make for my own eye in that situation.

The pinhole lens, the IC-8 Apthera, is a third option for irregular corneas. It has a small central opening, a bit like stopping down a camera, which blocks the scattered rays coming through the irregular parts of the cornea and only lets the central, well-focused ones through. It gives some depth of focus as well. The results in RK eyes have been encouraging: across the published series, 75% to 100% of eyes got to 6/12 or better without glasses, and in a group of 23 eyes followed for five years, unaided distance and intermediate vision held at 6/9 or better. The catch is glare. The small opening also cuts contrast in dim light and makes the retina harder to examine. That’s why I only put it in one eye, and use a standard lens in the other so you keep your night vision and contrast.

When it’s the cornea that needs fixing

Now and then the cornea is so unstable, or has drifted so far long-sighted, that choosing a lens carefully isn’t enough on its own and it makes more sense to deal with the cornea first.

Cross-linking doesn’t help much here. People sometimes ask about it, reasonably enough, because it’s the treatment that stiffens keratoconic corneas. In my experience it does little for an RK cornea. The problem isn’t weak collagen spread through the cornea, it’s a set of deep cuts that gape open, and cross-linking doesn’t close them.

The Greene lasso suture is something I can do for a cornea that has drifted a long way long-sighted or flexes unpredictably. It’s a circular purse-string stitch placed within the cornea around the central zone, crossing the old incisions, that pulls the centre back into a steeper and more stable shape. In a published series of 17 eyes, long-sightedness came down from an average of over four dioptres to close to zero. It’s a specialised procedure, but in the right eye it turns a cornea I can’t predict into one I can, and it can be done before or after the cataract surgery.

A corneal transplant is the last resort, for the small number of corneas that are too irregular and unstable for any of the above. Once there’s a stable cornea in place, cataract surgery becomes predictable again. It’s uncommon, and I mention it mainly so you know the option is there rather than assuming you have to live with poor vision.

Don’t forget the eye behind the cornea

There’s one more thing that’s easy to overlook, because the cornea gets all the attention. RK was done for short-sightedness, and most short-sighted eyes are short-sighted because they’re long from front to back. The cuts flattened the cornea to make up for that, and decades of extra flattening may have carried you the whole way into being long-sighted, but none of it changed the length of your eye. Behind that flat cornea is still a long, myopic eye.

That matters because long eyes have a higher rate of retinal detachment after cataract surgery. In a large Swedish study, every extra millimetre of eye length pushed the risk up by about 40%. A glasses prescription that reads “long-sighted” can make everybody, patient and doctor, treat the eye as low risk when it isn’t. So I measure the length of the eye rather than going by the prescription, I have a careful look at the retina before surgery and again afterwards, and I ask you to let me know straight away if you ever notice new flashes, floaters or a shadow coming across your vision, whether that’s a month after surgery or five years on.

One thing to bring

If you’ve still got any record of your glasses prescription from before the RK, dig it out. The best post-RK formulas use it.

Otherwise the operation itself is the same as anyone else’s, a day procedure with you asleep under sedation. If your laser surgery was LASIK rather than RK, it’s a different set of considerations and I’ve written about those separately.

The short version

Cataract surgery after RK works well, but it takes more planning and more patience than usual. Your vision will move around for a while, possibly six months. There’s a somewhat higher chance you’ll need glasses or a secondary lens afterwards. How many cuts you have decides which lenses I’ll offer: four keeps the premium options open, more than four generally rules them out, and the pinhole lens has a place in one eye. If the cornea itself is the problem there are ways to stabilise it. And the eye behind the cornea is still a long one, so the retina needs watching. Bring your old records and we’ll plan it properly.