Secondary cataracts are a good example of a medical term that was made up to simplify things, and then accomplished exactly the opposite. The same thing happened with the idea of cataracts being “ripe.” There is no such thing as a secondary cataract happening after successful cataract surgery, just like there is no such thing as ripeness to a cataract. The reason this matters is because the inevitable misunderstanding caused by these poor explanations will often cause people to worry about problems that don’t exist. It’s kind of the ophthalmologic equivalent of cooties, which were just an attempt to explain why the opposite sex is gross when you’re in kindergarten, but instead created panic over highly-contagious, non-existent disease.
When a cataract is removed, it isn’t a layer of cloudiness being removed. The lens in the eye itself is cloudy, and so the whole lens must be removed for the cloudiness to go away. This would cause a problem when it comes to seeing clearly afterward because lens in the eye has such a high prescription. Most human lenses have a prescription of around +15 diopters to +20 diopters—compare that to your strong reading glasses that are +2.50 diopters or so. The only way to have glasses strong enough to make up for the power of the missing lens is to make them as thick as shark aquarium glass.
There is, however, another way that is much more convenient.
That power can be put into an intra-ocular lens that is customized to have the exact right prescription to match what the eye needs. Now, not only is the cloudy lens gone, there is a new clear lens in its place with exactly the right focusing power to make glasses unnecessary altogether. But, we need a place to put it. And the perfect place is exactly where the old lens was.
The only way to get a new lens into the exact same spot that the old lens was is to put it inside the capsule that held the old lens. There is a very thin, transparent “skin” around the natural lens inside the eye that holds it in place. Successful cataract surgery is in large part the removal of the old cloudy lens without damaging the capsule that held it. Except for a small, circular opening made in the front of the capsule so that the old lens may be removed, the rest of the capsule must stay damage-free so it may hold the new artificial lens.
That’s where secondary cataracts come in.
The capsule is transparent, but it is also still natural human tissue. That means it is dynamic. It means it still can change over time. Because of that, it isn’t uncommon for the capsule holding this new, perfectly clear lens to lose a little bit of its transparency. This is called posterior capsular opacification (PCO). If you’re trying to call it a confusing and incorrect name, it would be called secondary cataracts. Sometimes it takes a couple months, sometimes a couple years. Sometimes it stays transparent for the rest of your life.
But when that capsule—the old transparent membrane that held both your old lens and now the new one—gets cloudy, you can imagine what the symptoms might be. Yes! The match the symptoms of a cataract almost line for line. The only difference is how you fix this problem. It involves a laser procedure (called a YAG laser capsulotomy) that takes about 30 seconds in clinic. It’s a laser you can’t see and can’t feel, and it fixes the problem instantly and permanently.
Once the laser procedure opens the capsule, the cloudy membrane isn’t in the way of your vision anymore. The only surface the light entering your eye must pass through is the clear, artificial lens. That new intra-ocular lens can never get a cataract, so you don’t have to worry about it changing over time. And because it can never get a cataract, it’s probably better we give up as soon as possible on the term “secondary cataracts” since it is inaccurate and misleading. It’s an uphill battle though, because posterior capsular opacification—while very easy to cure—sure doesn’t have the same ring to it.