Posterior Capsule Opacification: The Secondary Cataract and the YAG Laser That Clears It
By Pauline Driscoll | Medically reviewed by Mr Lewis Pereira, FRCOphth
Published April 17, 2026 · Last updatedMay 28, 2026 · Last reviewed June 2, 2026 · 3 min read
Key takeaways
- Posterior capsule opacification (PCO) is the clouding of the thin capsule left behind your lens implant, not the cataract growing back.
- It is the most common later issue after cataract surgery, affecting a meaningful minority over months to years.
- The fix is a YAG laser capsulotomy, a painless clinic procedure that usually takes around 5 minutes with no incision.
- The laser makes a small clear opening in the cloudy capsule, restoring vision, and the change is often dramatic and immediate.
- Once a capsulotomy has been done, PCO does not recur in that eye, because the central capsule has been opened.
Posterior capsule opacification (PCO), often called secondary cataract, is the clouding of the thin capsule deliberately left behind your lens implant during cataract surgery, and it is not the cataract growing back; it is fixed in minutes with a painless YAG laser1. It is the most common later issue after the operation, blurring vision months or years on in a way that feels like the original cataract, yet the cure is a quick clinic laser rather than more surgery2.
I had this myself, two years after my operation, and the panic of thinking my cataract had returned is exactly why I want to explain it properly. For the operation that comes first, see cataract surgery, and for the early healing afterwards, cataract surgery recovery.
What posterior capsule opacification actually is
PCO is the clouding of the posterior capsule, the thin, clear membrane left in place to hold your lens implant, when cells grow across it over time and make it hazy1. During cataract surgery the cloudy natural lens is removed from inside this capsule, and the new plastic lens is placed into the same capsule, which acts like a little bag holding the implant in position.
The key point, and the one that reassured me most, is that the capsule clouds, not the implant. The lens itself is permanent plastic and does not re-cloud. So although it feels like the cataract is back, what has happened is that the supporting membrane behind your perfectly clear implant has gone misty. That is why it is only nicknamed a secondary cataract, rather than being a true return of the original one.
How common it is and what it feels like
PCO is the most common later issue after cataract surgery, affecting a meaningful minority of people over months to years, with the exact rate varying by the lens implant and surgical technique3. The symptoms mirror a cataract: gradually blurred or misty vision, more glare and haloes around lights, and a feeling that hard-won clear sight is slipping away.
In my case, my vision had been wonderfully sharp after surgery, and then over a few months it began to feel like looking through a slightly smeared window again. My first thought was dread, that the whole thing had failed. When the optometrist explained it was the capsule clouding and not the lens, and that it was the commonest thing to happen later on, the relief was enormous. If your once-crisp vision starts fogging months or years on, this is a likely and very fixable cause.
The YAG laser capsulotomy that clears it
PCO is treated with a YAG laser capsulotomy, a painless clinic procedure that makes a small clear opening in the cloudy capsule and usually takes around 5 minutes, with no incision and no stitches1. You sit at a machine much like the one used for an eye examination, with numbing drops in and your chin on a support, and the laser creates a clean window in the centre of the capsule so light passes through clearly again.
What surprised me was how undramatic it was, despite the dramatic result. There were bright flashes and a clicking sound, sometimes a special contact lens is rested on the eye to steady it, and that was it. Afterwards I had a few new floaters and slightly blurry vision for an hour or two, which settled, and then my sharp vision was simply back4. It felt closer to a thorough eye test than an operation.
Why it does not come back, and what to expect
Once the laser has opened the cloudy capsule, PCO does not recur in that eye, because the central capsule has been permanently opened and cannot re-cloud across your line of sight1. You should not normally need the treatment repeated in the same eye, and the improvement in vision is often immediate and striking.
As with any laser treatment there are small, uncommon risks, such as a temporary rise in eye pressure, a small chance of retinal problems, and the new floaters mentioned above, which your eye team will discuss with you3. The honest summary is that this is one of the most routine and satisfying procedures in eye care: a few minutes of bright clicking lights in clinic, and the clarity you had after your cataract surgery is restored. If you want the wider question of whether cataracts themselves can return, that is covered separately in can cataracts come back.
References
- What is posterior capsule opacification (secondary cataract)?, American Academy of Ophthalmology. ↩
- Cataract surgery, NHS. ↩
- Cataracts in adults: management (NG77), NICE. ↩
- Cataract surgery patient information, Royal College of Ophthalmologists. ↩
Common questions
What is posterior capsule opacification?
It is the clouding of the thin, clear membrane called the posterior capsule that is deliberately left in place during cataract surgery to hold your lens implant. Over months or years, cells can grow across this capsule and make it hazy, blurring vision in a way that feels like the original cataract returning. It is the most common later issue after cataract surgery and is easily treated.
Is PCO the cataract coming back?
No. A cataract cannot come back, because the cloudy natural lens was removed and replaced with a permanent plastic lens that does not re-cloud. What clouds in PCO is the capsule behind that implant, not the lens itself, which is why it is nicknamed a secondary cataract rather than being a true recurrence. The symptoms feel similar, but the cause and the treatment are different.
How is posterior capsule opacification treated?
With a quick procedure called a YAG laser capsulotomy. The laser makes a small, clean opening in the middle of the cloudy capsule, letting light pass through clearly again. It is done in clinic while you sit at a machine like the one used for an eye examination, takes around 5 minutes, needs no incision or stitches, and is painless apart from a bright light and the clicking of the laser.
Does the YAG laser hurt?
No, it is painless. Numbing drops are usually used, you rest your chin on a support, and a special contact lens may be placed on the eye to steady it. You see bright flashes and hear clicking as the laser works, but there is no pain. Afterwards you may notice some new floaters and slightly blurred vision for a short while, which settle.
How common is PCO after cataract surgery?
It is the most common later complication of cataract surgery, affecting a meaningful minority of people over the months and years after the operation. Rates vary with the type of lens implant and surgical technique. Because it is so treatable, it is generally regarded as a minor and expected late finding rather than a serious complication of the surgery itself.
Can posterior capsule opacification come back after laser treatment?
Not in the central area that has been treated. Once the YAG laser has made an opening in the cloudy capsule, that clear window stays open, so the same clouding does not return across your line of sight. You do not normally need the treatment repeated in the same eye. Each eye is treated separately if both develop PCO.
What are the signs of PCO?
The symptoms feel like the original cataract: gradually blurred or misty vision, increasing glare and haloes around lights, and a sense that your once-clear vision is fading again, often months or years after surgery. If your sight was crisp after the operation and is now slowly clouding, it is worth an eye check, as PCO is a common and very treatable cause.
Written by Pauline Driscoll. Medically reviewed by Mr Lewis Pereira, FRCOphth.
Our guides are written from personal experience and reviewed by a qualified clinician for accuracy. Read our editorial policy.
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