Laser eye surgery

What it does

Laser vision correction reshapes the cornea — the clear front surface of the eye — so that light focuses on the retina without help from a lens in front of it. It treats short sight and long sight and astigmatism, which are all consequences of the eye's optics not matching its length.

It is a genuine alternative to glasses and contact lenses rather than a cure for anything. The eye is not made healthier by it; its focus is adjusted.

The three kinds of procedure

Clinics market these as meaningfully different choices. They are different in how they are done and in what recovery feels like, and much less different in where they end up.

LASIK creates a thin flap in the cornea with one laser, lifts it, reshapes the tissue underneath with a second, and lays the flap back without stitches. Recovery is the fastest of the three and many people are back at work the following day.

Surface treatments — PRK, LASEK and TransPRK — remove the outermost layer of the cornea rather than making a flap, then reshape the surface directly. The three differ only in how that layer is removed: by the surgeon, by loosening it with alcohol, or by the laser itself. The eye is often very sore while the layer regrows, and full visual recovery takes around three months.

Lenticule extraction — SMILE and its relatives — uses a laser to define a lens-shaped disc of tissue inside the cornea and removes it through a small incision, with no flap. Recovery is a little slower than LASIK, though the surface of the eye may settle slightly sooner.

The point worth holding on to: by three months the visual results are reported as equally good across all three. The choice between them is driven by corneal thickness, prescription, the surgeon's assessment and how much recovery discomfort is acceptable — not by one being better at correcting vision.

Who it suits

The basic requirements are being over eighteen and having a prescription that has been stable, meaning it has not shifted by more than half a dioptre in two years. A prescription still changing is a reason to wait rather than a reason to decline.

The usual treatable range runs to around −10 dioptres of short sight, +4 of long sight and 6 either way of astigmatism. Stronger prescriptions can sometimes be treated; some weaker ones are better served by a lens implant instead, which is a different operation worth asking about rather than assuming laser is the only option.

Cataracts rule it out, as do certain problems with the surface of the eye. One caution from the Royal College of Ophthalmologists is worth repeating: some contact lens wearers are wrongly told they have dry eye and are unsuitable, when the discomfort was the lenses. A second opinion is reasonable.

What to expect

The realistic promise is vision comparable to wearing contact lenses, without the lenses. The great majority of people who have it are satisfied with the result.

What it is not is a guarantee of never needing glasses. Glasses may still be wanted for some tasks, reading in particular for anyone past their forties. Vision can take up to two years to settle fully, and up to one person in ten needs a second treatment to fine-tune the result — which is normal rather than a failure, but worth knowing before rather than after, along with whether the clinic includes it.

Recovery

The procedure takes about half an hour for both eyes, under anaesthetic drops, and is done as a day case.

After LASIK or lenticule extraction, normal washing and showering resume the same day, and gentle exercise from day one. After a surface treatment, that waits until the bandage contact lenses come out, usually somewhere between the fourth and seventh day — and that first week is genuinely painful, which is the main reason to know in advance which procedure is planned.

Common and expected in the early weeks: dry, gritty eyes and intermittent blurring; glare, halos, starbursts and ghosting around lights, which can make night driving difficult at first; and red blotches on the white of the eye after LASIK, which can take six weeks to clear and look worse than they are. Most of this settles within a few months.

Swimming is usually out for a week and contact sports for a month after LASIK. Drops matter, with a couple of minutes left between different ones, and review appointments are worth attending even when the eyes feel perfectly fine.

The risks

Set against the fact that this is elective surgery on a healthy eye, these are the ones that deserve a straight answer.

Dry eye and night-vision disturbance are the common ones. They usually improve over a few months, but in a minority they persist, and higher prescriptions carry more of this risk.

Ectasia is the one the screening is for: the cornea becomes progressively unstable in shape after treatment. It can sometimes be corrected without a transplant. This is why corneal thickness is measured carefully and why some people are turned down.

Infection or abnormal healing can scar the cornea, and scarring can need a transplant to repair.

Permanent serious loss of vision is rare. Fewer than one in five thousand people treated go on to need a corneal transplant. That is a small number, and it is not nothing, which is the honest way to put it for an operation nobody has to have.

It does not spare anyone reading glasses

This is the expectation most often got wrong, and the disappointment is avoidable.

Laser surgery reshapes the cornea. Presbyopia — the gradual loss of near focus that arrives in the mid-forties — happens in the lens inside the eye, and nothing done to the cornea prevents it. Someone treated for distance vision at thirty will still need reading glasses in their forties, on the same schedule as everyone else.

There is a particular sting for people who are short-sighted, because short sight means being able to read comfortably with the glasses off. Correct that for distance and the near vision that came free disappears with it. For some people this registers as a loss, and it is better considered beforehand.

From the mid-forties onwards surgeons often work around it deliberately, aiming for good distance vision in one eye and arm's-length vision in the other, so the two together cover more range. It is called micromonovision, it suits many people well, and it suits some people not at all — which is a conversation to have at the consultation rather than a detail to discover afterwards.

It is not available on the NHS

Laser vision correction for ordinary short sight, long sight or astigmatism is not an NHS procedure, and private medical insurance does not generally cover it either. It is paid for privately.

That has a consequence for how it is sold. This is a competitive consumer market with heavy advertising, and the useful questions at a consultation are about what is actually included: the total cost and what it covers, whether fine-tuning treatments are included and for how long, what follow-up is provided, and what happens — and who pays — if there is a complication. A clinic should be clear about all of that from the outset.

It is also worth asking directly which procedure is recommended and why, and whether a lens implant would suit better. A surgeon who has reviewed the measurements should have a specific answer.

What it changes afterwards

Two consequences last for the rest of a lifetime's eye care, and neither is widely known.

A treated cornea causes eye pressure readings to come out lower than they really are. Pressure is one of the measurements used in checking for glaucoma, so an artificially low reading can be falsely reassuring. Anyone who has had laser correction should say so at every eye test, and it is worth keeping a copy of the prescription from before the surgery.

It also slightly reduces the accuracy of the calculations used to choose the replacement lens in cataract surgery, which almost everyone needs eventually. Telling the cataract surgeon about previous laser treatment lets them allow for it.

Neither is a reason not to have the surgery. Both are reasons to keep the paperwork and mention it, decades later, when it no longer feels relevant.