Cataract surgery on both eyes: at the same time or one after the other?

Two ways of doing it

Cataract almost always affects both eyes, often to different degrees. We usually start with the eye that is more troublesome. The second is operated on afterwards, generally a few weeks later.

Another approach is to operate on both eyes on the same day, one after the other, as two separate procedures: instruments, sterile drapes and products are changed between the two. It is common in some countries: in Sweden, more than 92,000 operations of this kind were recorded over sixteen years. It reduces the number of trips and the costs.

What the research says about the results

The question has been well studied. A Cochrane review, which brought together fourteen studies and more than 276,000 patients, concludes that there is probably no important difference in results between the two approaches. It points out that the evidence remains limited, and of moderate to very low quality depending on the criteria.

The most recent trial comes from the Netherlands. In ten hospitals, 865 patients were randomly assigned to surgery on the same day or in two stages. The second eye reached the intended correction, to within one dioptre, in 97% of cases on the same day and 98% in two stages. The authors had only included patients with no particular risk of infection or of a surprise in the lens implant calculation.

Not all studies point in exactly the same direction. An American registry covering 1.8 million patients found slightly poorer vision when both eyes were operated on the same day, by one to three letters on the reading chart. A large Californian study, for its part, found no difference. The American authors themselves acknowledge that this gap does not necessarily matter in daily life.

The risk that gives pause: infection of both eyes

The most feared complication after cataract surgery is endophthalmitis, an infection inside the eye. It is rare. In the Cochrane review, it occurred in 1 patient out of 14,076 operated on the same day, and 55 out of 556,246 operated on in two stages. The Swedish registry found one case per 6,600 operations, and only one patient infected on both sides.

So the risk is not higher. But when it occurs, it can affect both eyes at once. In Denmark, in 2022, three patients operated on the same day at the same clinic were infected in both eyes by the same germ, probably following a breach of sterility that day. One of them lost an eye. This is very rare, and teams who perform this surgery have strict protocols to prevent it. It is nonetheless the scenario I want to rule out.

Why I operate on one eye at a time

The first reason is infection. By operating two weeks apart, I check that the first eye is doing well before touching the second. If there were a problem, the other eye would be spared.

The second reason concerns the lens implant calculation. This calculation is based on very precise measurements, but it keeps a small margin of error. The result in the first eye tells me how your eye has responded, and I can adjust the implant for the second. An English study of 2,129 patients showed this: when the first eye was slightly off target, taking that gap into account raised the share of second eyes within half a dioptre of the target from 56% to 75%.

This is even more useful if you have chosen a particular implant, or if we are aiming for different vision in each eye. I discuss this with you when choosing the implant. The second eye is also an opportunity to adjust course if the first does not quite suit you.

Between the two operations

The two-week interval is not always comfortable. The operated eye sees better, the other not yet, and your glasses no longer suit the operated eye. Some patients feel a little unbalanced. This only lasts until the second eye is operated on. Having the lens removed from your glasses on the operated side can make you more comfortable.

The first eye is checked two days after the operation. The second is operated on two weeks after the first, then both eyes are checked at one month. Final glasses, if needed, are prescribed at that point. The full process is described on the cataract page.

Is it really worth operating on the second eye?

Once the first eye has been operated on, some patients see well enough to wonder whether the second operation is worthwhile. Most of the time, it is. An English trial published in the Lancet compared patients who had their second eye operated on within six weeks with others who waited seven to twelve months. Vision measured on the reading chart changed little. On the other hand, those who had been operated on reported far fewer difficulties in daily life, particularly with reading, and saw depth much better.

Seeing with two eyes means judging distances, steps and kerbs better. For an older person, this is not a detail. I never push anyone to have surgery, but I advise against leaving the second eye waiting for months without good reason.

If you have other questions about the process, the frequently asked questions page covers several of them. The pre-operative assessment is the right time to talk about it with me.

Sources Dickman MM, Spekreijse LS, Winkens B, et al. Immediate sequential bilateral surgery versus delayed sequential bilateral surgery for cataracts. Cochrane Database Syst Rev. 2022;4(4):CD013270.
Spekreijse L, Simons R, Winkens B, et al. Safety, effectiveness, and cost-effectiveness of immediate versus delayed sequential bilateral cataract surgery in the Netherlands (BICAT-NL study): a multicentre, non-inferiority, randomised controlled trial. Lancet. 2023;401(10392):1951-1962.
Friling E, Johansson B, Lundström M, et al. Postoperative endophthalmitis in immediate sequential bilateral cataract surgery: a nationwide registry study. Ophthalmology. 2022;129(1):26-34.
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Aristodemou P, Knox Cartwright NE, Sparrow JM, et al. First eye prediction error improves second eye refractive outcome results in 2129 patients after bilateral sequential cataract surgery. Ophthalmology. 2011;118(9):1701-1709.
Laidlaw DA, Harrad RA, Hopper CD, et al. Randomised trial of effectiveness of second eye cataract surgery. Lancet. 1998;352(9132):925-929.