Cataracts

What a cataract is

Behind the pupil sits a clear lens, about the size of a lentil, which focuses light onto the retina. A cataract is that lens becoming cloudy.

This matters to get right, because the common mental picture is wrong in a way that affects what people expect from treatment. A cataract is not a skin, a film or a growth over the surface of the eye. Nothing is covering anything. The lens itself, which was transparent, has lost its transparency — the proteins that make it up clump together and scatter light instead of passing it through cleanly.

That is also why the treatment is what it is. The lens cannot be polished or cleared. It is removed and replaced.

Cataract is the commonest cause of sight loss in the world, and almost uniquely among serious eye conditions, it is fully reversible. Most of what appears in the low vision article concerns conditions that can be slowed or managed. This one can be cured.

What it is like to have one

Cataracts usually develop slowly over years, which is the main reason they are missed. Vision that declines gradually feels normal, because there is no moment of change to notice.

The characteristic complaints are:

• vision that is less clear and distinct, in a general way rather than a blurry patch
• dazzle from headlights and streetlights, often the first thing people report
• difficulty adjusting when moving from shade into bright sunlight
• colours looking faded or yellowed
• double vision in one eye, which is to say double vision that persists when the other eye is covered

There is one more, and it is routinely misread as good news. Someone who is long-sighted may find they need their reading glasses less than they used to. That is not the eyes getting better. A clouding lens also changes its focusing power, and the shift happens to favour near vision for a while. A sudden improvement in reading vision in later life is a reason to get the eyes looked at, not a reason to feel lucky.

Regular sight tests pick up cataracts well before anyone notices them, which is the practical argument for going even when nothing seems wrong.

What causes them, and what does not

Ageing is the main cause, and the process is universal enough that cataract is better understood as something that eventually happens than as something that goes wrong. Most people who develop one in one eye go on to develop one in the other.

Other causes and contributors:

• injury to the eye, which can produce a cataract at any age
• diabetes
• long-term steroid medication
• other eye conditions, including glaucoma, uveitis, retinitis pigmentosa, and previous surgery for retinal detachment
• smoking, heavy alcohol use, being overweight, and ultraviolet exposure, all of which raise the risk

A very small number of babies are born with cataracts, which is a different situation handled by specialist paediatric services.

Two things that do not cause or worsen cataracts, both widely believed: using the eyes a great deal, and close work. Reading, screens and detailed work do not make a cataract progress faster.

Nothing has been shown to cure, slow or prevent a cataract — no drops, no supplement, no diet. Products claiming otherwise are not supported by evidence. What genuinely reduces the risk is the unglamorous list: not smoking, good sunglasses carrying a recognised safety mark, a healthy weight, and moderate drinking.

Nobody has to wait for it to ripen

This is the part most worth knowing, because the old rule is still repeated and it costs people years of avoidable difficulty.

Cataract surgery used to be delayed until the cataract was “ripe” — dense enough that vision had deteriorated badly. That approach is obsolete, and in England it has been explicitly overturned. The national guidance on cataracts in adults is unambiguous: access to cataract surgery is not to be restricted on the basis of visual acuity.

The reasoning is that reading letters on a chart is a crude measure of how much a cataract is costing someone. It misses glare and dazzle entirely, and it misses loss of colour discrimination — both of which can make driving at night impossible while the measured acuity still looks acceptable. The evidence review behind the guidance found no group, defined by starting acuity, that failed to benefit from surgery. Delay mostly produced avoidable loss of quality of life.

What determines referral instead is a conversation: how the cataract is affecting this particular person's vision and daily life, whether one or both eyes are involved, what surgery entails, what happens if they decline, and whether they want it.

That cuts both ways, and the second half matters as much as the first. Having a cataract is not in itself a reason to have surgery. If it is not interfering with daily life, leaving it alone is a legitimate choice and carries no penalty — it will not become harder to treat for having waited.

What the operation involves

It is among the most commonly performed operations in the health service, and it is briefer and less dramatic than most people expect.

A small incision is made at the front of the eye. The cloudy lens is broken up and removed, while the thin capsule that held it is deliberately left in place to support the replacement. An artificial lens is folded through the same incision and positioned inside that capsule. Stitches are usually not needed.

Most people are awake, under local anaesthetic. The sensation is of pressure, movement and cool liquid rather than pain. Sedation or a general anaesthetic is used where there is reason to.

The operation itself takes around twenty minutes. It is a day case, so nobody normally stays overnight, although a general anaesthetic or living alone may change that. Each eye is usually done separately, a few weeks apart, though some surgeons operate on both in one session for people at low risk.

One correction worth making, because it causes real confusion: standard cataract surgery is not laser surgery. The lens is broken up by ultrasound. Laser can be used for parts of the procedure, but there is little evidence it produces better results, and it is not widely available on the NHS. The laser treatment many people have heard about is a different, much later procedure, described further down.

The lens, and why glasses usually stay

The implanted lens is a fixed-focus lens. It normally lasts for life and needs no maintenance.

Fixed focus is the thing to understand. A natural young lens changes shape to focus at different distances; an implant cannot. Standard NHS surgery aims for good distance vision, which means reading glasses are usually still needed afterwards — a point that disappoints people who expected to throw their glasses away. The prescription is generally weaker than before, and some people find they need glasses for less than they used to, but expecting to need none is setting up for disappointment. This is the same focusing problem described in the presbyopia article, arriving by a different route.

Variable-focus and toric lenses, the latter correcting astigmatism, can reduce dependence on glasses further. They are generally available privately rather than as standard NHS provision, and they carry the same compromises as multifocal contact lenses do — some loss of crispness and more trouble with haloes at night.

Surgeons cannot guarantee a particular refractive outcome. The calculation is good but not exact.

Recovery

The eye is covered after surgery, usually until the following morning, after which it is bathed with cooled boiled water and a sterile swab. Prescribed drops are used for around four weeks and are not stopped early without being told to.

What is normal in the first days: a gritty sensation, blurred vision that improves steadily, mild redness, and slight swelling of the lid. Reading vision often needs a new prescription once things have settled, which is why new glasses are not ordered immediately.

What to avoid: rubbing the eye, soap or water in it, and eye make-up for two weeks; gardening, heavy lifting and similarly strenuous activity for two weeks; swimming for six weeks.

Most people are back at work after about a week, longer for dusty or physically demanding jobs. A check-up usually follows at around four weeks.

Driving depends on whether vision meets the legal standard, which is covered in the eye tests article, and the surgical team advises on when it is reasonable to start again.

The risks, in numbers

Cataract surgery is safe and routine, which is not the same as risk-free, and vague reassurance is less useful than figures.

For people with no other eye disease, the approximate frequencies are:

• around 2 in 100 find their vision is no better afterwards
• around 1 in 100 find it worse
• around 1 in 100 have a rupture of the lens capsule during surgery, which raises the later risk of retinal detachment
• around 1 in 1,000 have bleeding or infection severe enough to cost vision

Endophthalmitis, infection inside the eye, is the rare complication that does the most damage, and it is the reason for the drops and the care in the first weeks.

Pre-existing eye conditions change these numbers. Someone with macular degeneration or advanced glaucoma may have a cataract successfully removed and still see poorly, because the cataract was not the only thing limiting their sight. That is worth establishing in advance, since it reframes what success looks like.

When vision clouds again

Months or years after successful surgery, vision can become cloudy once more, with the same dazzle and blur as before. This is common, it is expected, and it is easily fixed.

It is not the cataract coming back. That is impossible — the lens was removed. What has happened is that the capsule left behind to hold the implant has itself thickened, which blocks light in much the same way. It is called posterior capsule opacification, and studies put it at somewhere around 10 to 20 per cent of people at some point after surgery.

The treatment is YAG laser capsulotomy, and this is the laser procedure people tend to remember and misattribute to the original surgery. A laser cuts a small opening in the thickened capsule so light passes through again. It takes five to ten minutes, there are no incisions and no stitches, and it is painless under anaesthetic drops. The appointment itself runs to a couple of hours because of dilating drops and checks beforehand, and driving home is not possible afterwards for the same reason.

Vision improves for most people, though it can take several days to settle fully. Temporary raised pressure in the eye, mild inflammation and new floaters are the common after-effects. Retinal detachment is a rare but serious one, more likely in people who are very short-sighted, and it can occur days to months later — which is why new floaters or flashes after this procedure are taken seriously rather than shrugged off.

When something is wrong

Most recoveries are uneventful. These are the things that are not waited out.

Contact the eye unit if vision is poor or getting worse, if the eye stays sensitive to light, or if it remains sore, red or sticky for more than a few days.

Seek urgent help, through the eye emergency service, for severe pain not relieved by ordinary painkillers, for a shower of floaters or flashing lights, or for redness, worsening vision or cloudiness within ten days of surgery.

The reasoning is the same as everywhere else in eye care: the conditions that threaten sight are treatable when caught quickly and much less so when they are not.