Secondary cataract (posterior capsule opacification): causes and treatment

A cataract is a clouding of the natural lens of the eye. The NHS explains that cataract surgery replaces the cloudy lens with an artificial lens, and that the surgeon makes a tiny opening through the front of the lens capsule, breaks up and removes the old lens and places the new lens inside the capsule, which holds it in position.

That capsule is the key to understanding a secondary cataract. Cambridge University Hospitals explains that the bag which enclosed the cataract is deliberately left behind to support the new lens. In a proportion of people the back of that bag gradually thickens and becomes opaque. The medical name is posterior capsule opacification, usually shortened to PCO, and it is also called a secondary cataract or after-cataract.

The name can be misleading. The cataract has not come back, because the natural lens has already been removed and a clear artificial lens put in its place. What has become cloudy is the supporting membrane behind that lens, so light has to pass through a misty film on its way to the retina.

Because the artificial lens itself does not cloud, PCO is a very different problem from the original cataract, and it is treated in a different and much simpler way. It is also a recognised, expected possibility rather than a sign that the first operation was done badly.

People usually describe the change as a return of the blur or mist they had before cataract surgery. Cambridge describes problems with vision such as misting or glare. In its list of possible complications the NHS includes vision that gets cloudy or blurry months or years after the operation, and in its advice about when to go to an optician it lists cloudy or blurry vision and finding it hard to focus.

Typical complaints include a slow, painless worsening of vision in the operated eye, increased glare from headlights or bright sunlight, and the sense that glasses no longer help as they did soon after surgery. The change is usually gradual, so it can be easy to adapt to without noticing until a reading or driving task becomes harder.

Cambridge adds that mild PCO may not cause symptoms but can progress over time and cause the vision to become more blurred. If that happens you can be referred for treatment later, so there is no need to rush into laser treatment when vision is still good.

Not every change in vision after surgery is a secondary cataract, and some changes need prompt help. The NHS advises getting help from NHS 111 if floaters, meaning dots and lines, suddenly appear or suddenly increase in number, if you get flashes of light, if a dark curtain or shadow moves across your vision, or if your vision suddenly becomes blurred. It says these could be signs of a detached retina.

The NHS also lists redness or pain in the eye, light or dark areas in the vision, and discomfort looking at bright light among the reasons to go to an optician. If you have severe pain, a rapidly worsening red eye or loss of vision, treat it as urgent and contact your eye clinic, NHS 111 or A&E.

PCO is identified by an eye examination. An optometrist or ophthalmologist checks your vision and examines the eye, and can also look for other reasons for blurred vision. Cambridge says that mild PCO may not cause symptoms.

This matters because the same symptom, blurred vision after cataract surgery, can have several causes. Treating PCO will only help if the capsule is the problem. That is why it is sensible to be seen by an optometrist or the hospital eye clinic rather than assuming the cause.

The NHS advises going to an optician if your vision gets cloudy or blurry, and Cambridge notes that you can be referred for the laser treatment. Some people also arrange laser treatment privately, which follows the same procedure.

The standard treatment is YAG laser capsulotomy. Cambridge describes how the laser is targeted precisely within the eye to create an opening in the middle of the misty capsule, clearing a path for light to enter the eye.

According to Cambridge, no special preparation is needed. A nurse checks your vision and puts drops in the eye to enlarge the pupil, which take around 20 to 30 minutes to work and leave your vision blurred for approximately four hours. A drop of local anaesthetic is given, a special contact lens is usually placed on the surface of the eye, and you rest your forehead against a headrest. The laser itself takes only a few minutes, you may hear clicking noises or see lights, and the procedure is painless. You are free to leave shortly afterwards.

Cambridge describes the YAG laser capsulotomy as a relatively minor laser procedure. Some people notice blurring or floaters afterwards, which generally settle within a few days. The laser can cause inflammation, and sometimes the pressure inside the eye rises shortly after the procedure, which may need further treatment, usually with eye drops. Occasionally the laser can make small marks on the surface of the artificial lens, which rarely causes problems but in a small minority of cases can result in glare.

Other side effects are described as very rare: detachment of the retina, swelling of the central part of the retina (macular oedema) or dislocation of the new lens. Cambridge says these complications are all potentially treatable. It advises contacting the eye clinic urgently if redness, pain or loss of vision gets worse after the procedure.

After treatment, you can usually resume activities as normal once the drops have worn off. Cambridge says your sight should be restored to the level you had after your original cataract surgery, you will still use glasses as before, and you may occasionally need an updated prescription for the best result.

For most people the outlook is good. Cambridge says that after treatment your sight should be restored to the level you had after the original surgery, unless you have another eye condition affecting your sight. If your vision does not improve as expected, your clinician will look for another cause.

It is sensible to mention any gradual change in vision to an optometrist. If you have had surgery on both eyes, each eye is treated separately, as the NHS notes that cataracts in both eyes are treated on separate days.