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Presbyopic Lens Exchange, or clear lens exchange
PreLex corrects presbyopia by replacing the natural lens with a multifocal lens implant. It is the same procedure as cataract surgery, applied to a lens that is still clear but has lost its elasticity and can no longer focus. The operation is permanent, and it removes any possibility of a future cataract along the way.
How it works
Presbyopia is not a disease of the cornea. It is the natural lens that stiffens and can no longer bulge to focus up close. PreLex therefore deals with the cause directly.
From around the age of 45, the lens gradually loses its flexibility. The ciliary muscle still contracts normally, but the lens no longer changes shape enough to focus up close. This is presbyopia, and it is unavoidable: no technique prevents or delays it.
PreLex, short for PREsbyopic Lens EXchange, means removing this stiffened (but still clear) lens and replacing it with a multifocal intraocular lens. This implant splits light between several focal points and restores distance, intermediate and near vision.
The procedure is exactly the same as cataract surgery. The only difference is timing: we operate before the lens becomes cloudy, for a functional reason, not because clouding has reduced vision.
The implant can correct myopia (short-sightedness), hyperopia (long-sightedness) and, in its toric version, astigmatism at the same time. That is where its value lies: it treats the whole optical problem in a single operation.
This is what sets PreLex apart from every other kind of refractive surgery. A working organ is removed from someone whose distance vision is often excellent. The decision is made with a cool head, after a full assessment and time to think it over, never in the enthusiasm of a consultation.
The operation is the same: I remove the natural lens and replace it with an implant. What changes is the state of the lens, and therefore the reason for operating.
With a cataract, the lens has become cloudy. Vision drops, colours look duller, driving at night becomes difficult. We operate to restore the vision the clouding has taken away, and the operation is covered by French national health insurance (Assurance Maladie).
With PreLex, the lens is still clear. The eye sees well at distance, but the stiffened lens can no longer focus up close. We operate to do without glasses, not to treat a disease: PreLex is refractive surgery and is not reimbursed.
The assessment decides. What makes it cataract surgery is not the clouding alone: it is how much the clouding gets in the way of daily life. Early clouding, or a cataract that does not yet affect vision, points towards PreLex. Cataract surgery
Step by step
The operation takes about twenty minutes. What surrounds it matters more: the assessment that decides on it, and the weeks of adaptation that follow.
This is the decisive step. It measures the eye's biometry, which is used to calculate the implant power for your eye, and checks the cornea by topography, the macula and optic nerve by OCT, and the quality of the tear film.
It also looks at your expectations and way of life: night driving, screen work, long spells of reading. These guide the choice of implant as much as the measurements do.
As a day case, under anaesthetic eye drops, with an eyelid speculum in place. One main incision at the limbus and one or two side-port incisions (paracenteses), a circular opening of the capsule (the capsulorhexis), then ultrasound fragmentation and aspiration of the lens, with the capsule preserved.
The multifocal lens is injected folded into the capsular bag, where it unfolds. The incision seals itself: a stitch is rarely needed.
You are awake and lying down, with your eyelids held open by a speculum. You feel no pain, only a sensation of pressure, and you can hear the instruments.
Your vision becomes strange: diffuse lights, coloured shapes, a feeling of looking through a kaleidoscope. This is normal and temporary. Feeling apprehensive before the operation is just as normal, and the team is there for that.
A protective eye shield at night for a few days, antibiotic and anti-inflammatory eye drops, no strenuous physical exertion, and above all no rubbing the eye.
Blurred vision and sensitivity to light are usual in the first few days. Vision becomes useful again within two to seven days, but because the implant is multifocal or EDOF, high-quality vision takes several weeks to several months to settle while the brain adapts (neuroadaptation). Vision stabilises within one to three months, sometimes up to six. The two eyes are operated on a few weeks apart.
The six stages of the operation: front view
Antiseptic cleaning of the eye surface, anaesthetic eye drops, then placement of an eyelid speculum.
One main incision at the limbus and one or two side-port incisions (paracenteses), with no stitches.
Continuous circular opening of the capsule, which is kept to hold the implant.
The lens, still clear but now stiff, is broken up and then aspirated. The capsule around it is preserved.
The multifocal lens is injected folded, then unfolds in the capsular bag. Its concentric rings split light between distance, intermediate and near.
Antibiotic injection, check that the incisions are sealed, protection of the eye.
Structure involved Lens removed Multifocal lens Capsule preserved
The choice
These are the two ways to correct presbyopia, and they are not meant for the same patients. One works on the cornea and leaves the lens to age. The other replaces the lens and leaves the cornea alone.
| PreLex | PresbyLASIK | |
|---|---|---|
| What is changed | The natural lens, replaced by a multifocal lens | The cornea, reshaped by laser into a multifocal surface |
| Durability | Permanent. A cataract can no longer develop | The lens keeps on ageing: a cataract is still possible, and will need surgery |
| Range of correction | Corrects high refractive errors, beyond the limits of the laser | Limited by the corneal thickness available |
| Type of procedure | Intraocular: the eye is opened | Corneal: the inside of the eye is not entered |
| Specific risks | Endophthalmitis, capsule rupture, retinal detachment: rare but real | Corneal complications, with no intraocular risk |
| Cost | Higher: operating theatre, anaesthesia and implant costs are added to the surgeon's fees. Not reimbursed, but often partly covered by top-up health insurance (mutuelle) | Lower, as the procedure takes place in the laser suite. Not reimbursed, but often partly covered by top-up health insurance |
| Usual age | From 55 | Between 45 and 55, while the lens is still clear |
| Location | Clinique Les Martinets, Rueil-Malmaison | Laser suite at Institut Voltaire, Paris 11th |
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Before 55, there is often some remaining ability to focus up close (accommodation) that it would be a pity to sacrifice, and the benefit of PreLex over laser does not yet justify the intraocular risk. Beyond that age, accommodation is used up, an early cataract often starts to form, and replacing the lens becomes the most logical option: presbyopia is treated and the cataract dealt with in advance, in a single procedure.
Expected side effects
These effects are not complications: they follow directly from the way the implant works. Because they are predictable, they must be understood and accepted before the operation.
| Its strengths | Its limits |
|---|---|
| Frequent night driving is the main reason to choose an EDOF lens over a multifocal one, or even to give up on multifocality altogether. | Halos and glare at night: a multifocal lens creates rings or starbursts around lights, especially at night and when driving. This is an optical property of the device, not a flaw in the operation. |
| Expectations must be stated clearly: the realistic goal is to do without glasses in the vast majority of everyday situations, not in all of them. | Reduced contrast sensitivity: by splitting light between several focal points, the implant gives less of it to each one. Subtle shades are harder to tell apart, especially in low light. |
| The first eye is a test: operating on the two eyes a few weeks apart lets us see how well you actually tolerate the lens before going on. | Fine print sometimes imperfect: for small print, or long reading in dim surroundings, occasional glasses may still be useful. |
| Everything depends on the health of the retina and cornea: a multifocal lens needs an eye that is otherwise perfect. That is what the assessment checks. | Neuroadaptation: the brain learns to pick out the sharp image from those the implant provides. Vision becomes useful again within two to seven days, but adaptation takes several weeks to several months, with vision stabilising in one to three months, sometimes up to six. |
Monofocal, monofocal plus, EDOF or multifocal: each type gives a different range of clear vision, and multifocality is not always the best compromise. These four profiles are described in detail on the page on lens implants.
Complications
The procedure is identical, so the risks are too. They are rare but real, and accepting them asks more of you here, because the operation is done for function and is not a medical necessity.
An infection inside the eye, despite strict asepsis. This is the most serious complication: it needs immediate treatment, and its effects range from a major loss of vision to the functional loss of the eye.
A tear in the thin membrane that supports the implant compromises its stability. The multifocal lens originally planned often has to be abandoned in favour of another model: the surgical plan changes during the operation.
A temporary swelling of the cornea blurs vision for the first few days. It usually clears up on its own.
More common in people with high myopia. It can lead to a major loss of vision if it is not operated on quickly, which is why you should know the warning signs.
Usually controlled with local treatment, and checked at the post-operative visits.
Calculation formulas have their limits, and every eye has its own particularities. A residual error may mean wearing glasses or having a second procedure. The risk is higher in patients who have already had corneal refractive surgery, because the altered cornea skews the measurements.
Previous LASIK, PRK or SMILE does not rule out PreLex, but it makes the implant calculation much harder. Be sure to bring your operation reports and your pre-laser measurements: they are what allow the right formulas to be applied and the margin of error to be reduced.
Indications
PreLex offers a lasting correction of presbyopia, but it does not suit everyone. What matters is less the presbyopia itself than the health of the rest of the eye.
SFO information leaflets (in French)
These leaflets are published by the Société Française d'Ophtalmologie (French Society of Ophthalmology). They describe the procedure, its results, its risks and the consequences of declining treatment. They serve as the basis for informed consent, but do not replace the consultation.
The questionnaire gives a first indication of laser or implant. The pre-operative assessment measures what cannot be guessed: your biometry, your cornea and the health of your retina.
Dr Emmanuel Halimi
Ophthalmic surgeon · RPPS 10100555084 · Medical Council of Hauts-de-Seine no. 92/23003
Page written and approved by the surgeon.
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