Lens surgery

The lens
and cataract

When the lens becomes clouded or too rigid, it is replaced with a custom-calculated intraocular lens. The choice of implant and the precision of the biometric calculation are the two levers that turn a functional surgery into a refractive one.

01 — Surgery

Cataract
surgery

A cataract is a progressive clouding of the lens — the eye’s natural lens, normally transparent. It causes a decline in vision, glare, impaired contrast perception and, sometimes, a change in refraction. The only treatment is surgical.

The procedure consists of removing the clouded lens by phacoemulsification — an ultrasound probe fragmenting the lens through a 2.2 mm micro-incision — then implanting an artificial lens to replace it. The procedure is performed as a day case, under topical (eye-drop) anaesthesia, and usually lasts ten to fifteen minutes.

Visual recovery is fast: most patients regain functional vision within 24 to 48 hours. The final refractive result stabilises over a few weeks, while corneal healing completes.

Technique

Phacoemulsification

Ultrasound fragmentation. 2.2 mm incision. No sutures. Day case.

Anaesthesia

Topical, with eye drops. Sedation if needed. No general anaesthesia in the great majority of cases.

Recovery

Functional vision within 24–48 h. Refractive result stable in 3 to 6 weeks.

Video — Cataract surgery Source: Clinique Saint-Pierre Ottignies
Lens surgery in five steps Five panels. First: a 2.2 mm micro-incision is made at the periphery of the cornea, usually without a suture. Second, seen from the front: a circular opening is made in the front capsule. Third: the lens is broken up and aspirated by a probe introduced through the incision. Fourth: the emptied capsular bag receives the folded implant, delivered by an injector. Fifth: the implant unfolds and centres itself in the preserved capsular bag. Lens surgery in five steps The same sequence, whether for a cataract or for a clear lens. 1 ACCESS 2.2 mm A 2.2 mm micro-incision at the edge of the cornea, usually without a suture. 2 CAPSULORHEXIS front view A circular opening is made in the front capsule, sized and centred on the visual axis. 3 PHACOEMULSIFICATION The lens is broken up and then aspirated. The clearer the lens, the less ultrasound energy is needed. 4 INJECTION The emptied bag is cleaned, then the folded implant is inserted through the same incision. 5 UNFOLDING The implant unfolds and centres itself in the original capsular bag, which will hold it for life. Local anaesthesia with drops, as a day case, one eye at a time. The procedure itself takes about ten minutes; allow a few hours at the clinic. The sequence is identical for a cataract and for a clear lens exchange: only the indication differs.
The five stages of the procedure
The risks of lens surgery, in orders of magnitude Four events placed on a logarithmic scale of frequency. A capsular veil treated with the laser affects about one person in ten within five years. Swelling of the macula, which usually resolves on its own, about one in a hundred. Retinal detachment is rare, with a frequency that varies widely with the eye and is about twice as high after clear lens exchange. Intraocular infection, the most serious event, occurs in about one case in five to ten thousand. The risks, in orders of magnitude Rare, but real. Here is how they stand in relation to one another. Logarithmic scale: from one gridline to the next, the event is ten times rarer. 1 in 10 1 in 100 1 in 1,000 1 in 10,000 Capsular veil treated with the laser within the following five years about 1 in 10 Swelling of the macula usually resolves on its own about 1 in 100 Retinal detachment higher beyond 26 mm of axial length about twice as frequentafter clear lens exchange Intraocular infection the most serious event about 1 in 5,000 to 1 in 10,000 These orders of magnitude come from the international literature and assume uncomplicated surgery on an eye with noparticular risk factor. They do not replace an assessment of your own eye: diabetes, a membrane on the retina or a verylong eye shift these figures. The antibiotic injected at the end of surgery divides the infection risk by about five. Figures from the international literature, reviewed in August 2026.
Orders of magnitude
Posterior capsule opacification and laser capsulotomy Three cross-sections of the operated eye. After surgery, the back wall of the capsular bag stays transparent behind the implant. Over time, cells cover it and it thickens: vision veils over again. A central opening is then made with the laser through the pupil, without any incision. The late veil: the posterior capsule This is not a cataract growing back, but the capsule left in place becoming cloudy. AFTER SURGERY clear posterior capsule The capsular bag is preserved. Its backwall stays transparent behind theimplant. SECONDARY CLOUDING clouded posterior capsule Cells gradually cover it: vision veilsover again, sometimes months oryears later. LASER CAPSULOTOMY (YAG) central opening made with the laser A central opening is made with thelaser, through the pupil. A fewminutes, no incision, no anaesthetic. This is the most ordinary late event after lens surgery, it is harmless, and it is treated only once.Worth knowing: once the capsule is open, exchanging the implant becomes more delicate. That is a reason to wait untilvision has settled before performing the laser, rather than scheduling it at the first sign of veiling.
The posterior capsule after surgery
02 — Expanded indication

Refractive cataract
and clear lens

Refractive cataract surgery

In standard cataract surgery, the main goal is to restore clear vision by replacing the clouded lens. Refractive cataract surgery goes further: from the planning stage it incorporates a precise optical-correction goal, aiming to reduce or remove the dependence on glasses after surgery.

This involves more demanding biometry, the choice of a precision implant (EDOF, multifocal, toric), and an in-depth discussion of the patient’s visual expectations. The refractive approach is offered as a matter of course to patients who are candidates for it.

Clear-lens surgery

In some presbyopic patients — whose lens is still transparent but has lost all ability to accommodate — the same procedure can be performed in the absence of a cataract. This is known as clear-lens surgery (refractive lens exchange, RLE).

The indication is discussed case by case. It is particularly relevant in high hyperopes, or in patients whose cornea and anterior segment do not allow correction by laser or phakic implant. It permanently removes the risk of a future cataract, since the natural lens is removed.

Cataract or clear lens: the same operation, two situations Three cross-sections of the eye. On the left, a lens clouded by cataract. On the right, a lens that is still transparent but no longer focuses at near. Both lead to the same operation, shown in the centre: the lens is replaced by an implant placed in the preserved capsular bag. The operation and its risks are identical; only the reason for undertaking it differs. Cataract or clear lens: the same operation, two situations What differs is not the surgery, but the reason for doing it. CATARACT clouded lens The lens has become cloudy. Visiondeclines, and no pair of glassesrestores it. THE SAME SURGERY implant in the preserved bag The operation, its recovery and itsrisks are identical in bothsituations. CLEAR LENS transparent lens The lens is still clear, but it nolonger focuses at near and thecorrection remains strong. In one case, surgery repairs lost vision: the benefit is certain and the decision straightforward. In the other, it anticipatesan optical need: it is a choice, carrying the same operative risks for a benefit measured in convenience.What differs is the balance behind the decision, not the operation.
Cataract or clear lens
What the implant replaces and what it does not Three cross-sections of the front of the eye. While the lens is flexible, it bulges under the action of the ciliary muscle and zonules to focus at near. Once hardened, it no longer bulges and near vision is lost: this is presbyopia. After surgery, the implant placed in the preserved capsular bag has a fixed shape: accommodation is not restored. What the implant replaces — and what it does not The natural lens changes shape. An implant does not. FLEXIBLE LENS solid line: at rest · dotted: accommodating The lens is flexible. Driven by the ciliary muscle, it bulges to bring near objects into focus: this is accommodation. HARDENED LENS almost no accommodative amplitude The lens hardens. It no longer bulges: near vision is gradually lost. This is presbyopia. LENS REPLACED the original capsular bag is preserved The implant has a fixed shape. It restores a sharp image, but it does not change shape: accommodation is not restored. No implant restores accommodation. So-called multifocal implants do not reproduce it: they create several simultaneous points of focus by sharing out the light entering the eye. That sharing is the source of the trade-offs set out in the diagrams that follow.
Accommodation and its loss
What can be undone and what cannot Three cross-sections compared. The corneal laser permanently removes corneal tissue, whose original profile is shown as a dotted line. The ICL implant is added behind the iris, in front of the preserved natural lens, and can be removed. Lens exchange removes the lens, replaced by an implant in the capsular bag: the step cannot be undone, even though the implant itself remains changeable. What can be undone — and what cannot Three surgical routes, three degrees of reversibility. CORNEAL LASER dotted: the original corneal profile (tissue removal exaggerated for clarity) The laser permanently removes corneal tissue. This cannot be undone; a touch-up remains possible if thickness allows. ICL IMPLANT natural lens preserved The implant is added behind the iris, in front of the lens, which stays put. It can be removed: the eye returns to its previous state. LENS EXCHANGE lens removed, capsular bag preserved The lens is removed. That cannot be undone. The implant itself can be changed — at the cost of a second intraocular operation. REMOVABLE PERMANENT ICL implant Lens exchange* Corneal laser * A lens that has been removed cannot be put back; only the implant remains changeable.
What can be undone and what cannot
03 — Choosing the implant

Choosing
your implant

The choice of implant is the central refractive decision in lens surgery. It takes into account the ocular anatomy, the refractive history, the visual habits and the patient’s expectations regarding independence from glasses. No implant is universally superior: each family suits a different patient profile.

01

Monofocal

A single point of focus

The monofocal implant corrects refraction for a single distance — generally distance vision. Near vision and, to a lesser extent, intermediate vision require glasses.

It is the implant that offers the best refractive predictability and the best optical quality in night vision. It is indicated in patients whose lifestyle is compatible with occasional spectacle wear, or in those for whom refractive safety takes priority over spectacle independence.

  • Most predictable refractive result
  • Maximum optical quality at distance
  • Very few halos or glare
  • Reading glasses usually needed

Suitable profile

Patients who accept reading glasses. Pilots. Heavy night driving. Macular history or moderate glaucoma.

02

EDOF

Extended depth of focus

The EDOF implant (Extended Depth of Focus) does not create several distinct focal points: it stretches the range of sharpness from distance to intermediate vision (computer, dashboard). Near vision still requires glasses in low light, but is often satisfactory in bright light.

Night-time optical quality is better than with a multifocal, with fewer halos. Neuroadaptation is shorter and easier. It is often the best-tolerated compromise for patients wanting more independence without sacrificing night-vision quality.

  • Excellent distance and intermediate vision
  • Moderate night-time halos
  • Shorter neuroadaptation than with the multifocal
  • Occasional reading glasses possible in low light

Suitable profile

Active patients wanting to reduce their dependence on glasses. Regular driving. Special cases: after radial keratotomy (see dedicated section).

03

Multifocal

Aims for full spectacle independence

The multifocal implant creates several focal points (distance, intermediate, near) through concentric diffractive zones. When selection is rigorous and neuroadaptation complete, the great majority of patients no longer need glasses day to day.

In return, halos and glare around night-time light sources are more frequent than with the other families. A period of neuroadaptation is needed (a few weeks to a few months). Selection requirements are stricter: maculopathy, significant glaucoma or an irregular cornea contraindicate this implant.

  • Best potential independence from glasses
  • More frequent night-time halos and glare
  • Neuroadaptation required
  • Stricter selection criteria

Suitable profile

Patients strongly motivated by spectacle independence. Regular cornea. No macular disease or significant glaucoma.

Sharing out the light between points of focus Three optical diagrams compared. A monofocal implant concentrates all the light on a single point of focus on the retina. An extended focus implant lengthens that zone of focus towards intermediate vision. A trifocal implant creates three points of focus: only one is on the retina at a given moment, the other two arriving out of focus and superimposed, which explains the loss of contrast and the halos. Sharing out the light An implant does not create extra sharpness: it shares out the light that enters the eye. MONOFOCAL A single point of focus retina How the incoming light is shared EXTENDED FOCUS A continuous range of focus, but a limited one range of focus retina TRIFOCAL Three points of focus near intermediate far retina the other two focal points arrive out of focus far intermediate near optical losses Proportions are schematic: they vary between implant models. Every added point of focus takes light from the others, and some of it is lost. Less contrast in dim light and halos at night are therefore not complications: they are how these implants work.
How an implant splits incoming light
Where vision is sharp, by implant type Four curves comparing the sharpness obtained from distance vision to reading. The monofocal is sharp at distance only. Micro-monovision extends the range towards intermediate. Extended focus covers far and intermediate. The trifocal covers all three distances but shows dips between them. Under each curve, a bar marks the distances where glasses remain useful. Where vision is sharp, by implant type No profile is sharp everywhere: each one puts the sharpness in a different place. distances where glasses remain useful MONOFOCAL A single point of focus sharp blurred far intermediate reading Sharp vision at distance.Glasses for intermediateand for reading. MONOFOCAL + MICRO-MONOVISION One eye set slightly myopic sharp blurred far intermediate reading Far and intermediate often withoutglasses. Requires tolerating adifference between the two eyes. EXTENDED FOCUS A continuous range of focus sharp blurred far intermediate reading Far and intermediate covered.Glasses for prolonged readingor small print. TRIFOCAL Three points of focus sharp blurred far intermediate reading All three distances covered, withdips between them and slightlylower contrast. These curves are orders of magnitude, not promises: the result depends on the eye and on neuroadaptation.The choice is therefore not about the widest curve, but about the distances you actually use.
Range of sharp vision by implant family
Night vision and neuroadaptation At the top, the same light source seen at night according to the type of implant: a sharp point with a monofocal, a faint halo with extended focus, concentric rings with a trifocal. Below, a curve shows that the perceived disturbance falls sharply over the first months and then settles at a low but non-zero level in a minority of patients. Night vision and neuroadaptation The same light source at night, according to the optical profile of the implant. MONOFOCAL Sharp point of light, slight veiling possible. EXTENDED FOCUS Faint halo, sometimes a streak. TRIFOCAL Concentric rings around light sources. Schematic depiction of a car headlight seen at night. HOW THE DISTURBANCE CHANGES OVER TIME first weeks 3 to 6 months beyond disturbance none residual in a minority The brain learns to ignore these stray images: the disturbance fades markedly over the months, without disappearingcompletely in everyone. If it remains disabling, the implant can be exchanged — that is a second intraocular operation.
Night vision and neuroadaptation

Toric implants

Each of these families exists in a toric version, incorporating a correction of corneal astigmatism. The toric model is selected for refractive cataract surgery when preoperative astigmatism exceeds about 0.75 to 1.00 cylindrical dioptres. Its axial alignment is calculated preoperatively and checked intraoperatively.

Combined surgery

Cataract
and glaucoma

When glaucoma and a cataract coexist, surgery on the lens also makes it possible to act on the drainage of aqueous humour, and the choice of implant takes the glaucoma into account. A micro-stent can be added during the same procedure.

Cataract and glaucoma →

04 — Special case

Calculation after
previous refractive laser

Corneal laser surgery (LASIK, transPRK, PRK) changes the curvature of the anterior cornea. Now, the standard biometric formulas used to calculate the power of a cataract implant were developed for unoperated corneas: they use corneal keratometry (the curvature measurement) to estimate the overall refractive power of the cornea, which is no longer valid after laser ablation.

After a myopic laser (which flattens the central cornea), the standard formulas overestimate the residual corneal power and lead to an underpowered implant → risk of postoperative hyperopia. After a hyperopic laser (which steepens the cornea), it is the opposite: risk of residual myopia.

Specialised formulas and dedicated calculators (Barrett True K, ASCRS Post-Refractive IOL Calculator) make it possible to correct this bias. Accuracy improves when the pre-laser data are available: initial refraction, correction performed, pre-laser keratometry.

What the surgeon needs

  • Pre-laser refraction if available
  • Correction performed (dioptres treated)
  • Technique: LASIK, transPRK, PRK
  • Approximate date of the procedure
  • Operative reports if accessible

What this means for you

In the absence of pre-laser data, the calculation is still possible but the margin of uncertainty is wider. It is important to be aware of this before surgery: the refractive result may deviate further from the intended target, and a residual correction with glasses remains possible.

05 — Special case

Options after
radial keratotomy

Radial keratotomy (RK) is a surgical technique used from the 1970s to the 1990s, which corrected myopia with radial incisions on the cornea. It has been largely superseded by the excimer laser, but many patients operated on at that time now approach cataract surgery with a deeply reshaped cornea.

01

Diurnal variation of vision

The radial scars have reduced rigidity. At night, lying down, the incisions open up slightly, which flattens the cornea and changes the refraction. On waking in the morning, vision can be noticeably different from what it is at the end of the day, once the incisions have tightened again. This variability persists for decades after the keratotomy and cannot be removed surgically.

For the implant calculation, this means keratometry varies depending on the time of measurement: biometry performed in the morning may give a different result from one taken in the afternoon. Repeated measurements and a complete corneal tomography are essential.

02

Irregular astigmatism and high optical aberrations

The radial incisions create surface irregularities that generate higher-order aberrations (HOAs): coma, spherical aberration, trefoil. These aberrations cannot be corrected by a simple sphero-cylindrical correction (glasses or a standard implant) and degrade vision quality, particularly at night.

A complete corneal tomography is required to map these irregularities, quantify the aberrations and guide the choice of implant.

Two options to consider

EDOF

Reducing diurnal variation

In patients with significant diurnal variation, the EDOF implant may be offered not to improve intermediate vision — the usual advantage of this family — but for a reason more specific to radial keratotomy:

Its extended range of focus acts as a refractive buffer. When the corneal curvature fluctuates over the day and slightly shifts the focal point, the EDOF “absorbs” part of these fluctuations — where a monofocal would be more sensitive to each variation in keratometry.

The goal is to improve day-to-day visual stability, not to eliminate the variability (which remains linked to the corneal scars).

IC-8 Apthera

Reducing the impact of high HOAs

The IC-8 Apthera implant (Bausch + Lomb) incorporates a central opaque ring with a 1.36 mm pinhole. Like a photographic aperture, this pinhole narrows the incoming light beam, which increases depth of focus and greatly reduces the impact of irregular optical aberrations on the perceived image quality.

For patients with radial keratotomy and very high HOAs and severe irregular astigmatism, the IC-8 can offer an improvement in vision quality that conventional implants cannot achieve.

The IC-8 reduces the overall brightness reaching the retina. It is contraindicated in cases of macular disease or any optic-nerve condition limiting sensitivity.

Biometric calculation — a point of attention

The standard biometric formulas fail on two counts after radial keratotomy: they account neither for the corneal irregularities nor for the variability of the measurements. The calculation must be performed with adapted formulas, measurements repeated at different times of day, and a complete tomographic analysis. The residual margin of uncertainty is wider than in standard cataract surgery — the patient must be informed of this.

Your assessment determines
the right implant

Biometry, corneal topography, refractive history, visual expectations: the choice of implant is a decision built during the preoperative consultation, not before.

Book an appointment → Patient journey

Frequently asked questions

What does cataract surgery involve?

A cataract is the progressive clouding of the lens, the eye’s natural lens; its only treatment is surgical. The procedure fragments the clouded lens with ultrasound (phacoemulsification) through a 2.2-mm micro-incision without sutures, then replaces it with an implant. It is performed as day surgery, under local anaesthesia with drops, and generally lasts ten to fifteen minutes.

Is it painful?

Anaesthesia is given with drops, sometimes supplemented by light sedation; general anaesthesia is needed only in rare cases. The procedure is not painful.

When will I recover my vision?

Most patients regain functional vision within 24 to 48 hours. The final refractive result stabilises over three to six weeks, as healing completes.

Are both eyes operated on the same day?

It depends on the procedure. For a cataract, the two eyes are usually operated separately, one to two weeks apart — which allows the result of the first eye to be verified before operating on the second. For a refractive lens exchange, bilateral sequential surgery is generally offered on the same day (both eyes one after the other, during the same session).

Can the cataract come back after surgery?

No: the removed lens does not re-form. It can happen, however, that the thin membrane supporting the implant — the posterior capsule — becomes cloudy over time: this is posterior capsule opacification, often called a "secondary cataract". It is treated in a few minutes by a painless laser procedure, without any new incision.

What is "refractive" cataract surgery?

In standard cataract surgery, the aim is to restore clear vision. The refractive approach goes further: from the planning stage it incorporates an optical-correction objective, to reduce or eliminate your dependence on glasses. It requires more demanding biometry and the choice of a precision implant, and it is systematically offered to patients who are candidates for it.

Can surgery be performed without having a cataract?

Yes: in certain presbyopic patients whose lens is still clear but has lost all accommodation, the same procedure can be performed without a cataract — this is called refractive lens exchange. The indication is discussed case by case; it is particularly relevant in high hyperopes or when the cornea allows neither laser nor a phakic implant. As the natural lens is removed, it permanently eliminates the risk of a future cataract.

Monofocal, EDOF, or multifocal: how to choose?

No implant is superior in absolute terms: each family suits a different profile. The monofocal offers the best predictability and the best night-vision quality, but requires reading glasses. The EDOF extends sharpness from distance to intermediate with few halos, fine reading possibly requiring glasses in low light. The multifocal aims for full independence from glasses, at the cost of more frequent night halos and a neuroadaptation period. The choice is built at the assessment, according to your anatomy, your habits, and your expectations.

Do halos after a multifocal implant go away? How long does adaptation take?

With a multifocal, halos and glare around lights at night are more frequent at first. The brain gradually learns to filter them out: this neuroadaptation takes from a few weeks to a few months. It is shorter and easier with an EDOF, whose halos are milder — one of the elements discussed when choosing.

Will I still need to wear glasses afterwards?

It depends on the implant chosen. With a monofocal, reading glasses are usually still needed. With an EDOF, distance and intermediate vision are independent, fine reading possibly requiring a little help in low light. With a well-selected multifocal, the great majority of patients manage without glasses day to day — though no implant guarantees total independence in every situation.

Can my astigmatism be corrected at the same time?

Yes. Each implant family is available in a toric version, which incorporates the correction of corneal astigmatism. This option is chosen from about 0.75 to 1.00 diopter of astigmatism; the implant’s axis is calculated before the procedure and verified during it.

I have already had laser surgery: is it more complicated to calculate my implant?

The laser altered the curvature of your cornea, which skews the standard calculation formulas and can leave a residual correction after surgery. Specialised formulas correct this bias, all the better when your pre-laser data are available (initial refraction, diopters treated, technique, date). Without them, the calculation is still possible but with a wider margin of uncertainty, which it is important to be aware of beforehand.

I have had radial keratotomy: what does that change?

This older technique leaves a cornea weakened by incisions, with vision that often varies between morning and evening and high optical aberrations. Calculating the implant requires repeated measurements at different times of day and a complete tomography, with a wider margin of uncertainty. Depending on your case, particular implants — an EDOF to dampen the variability, or a small-aperture (pinhole) implant to reduce the impact of aberrations — may be considered.

Have you already had laser surgery or radial keratotomy? Your case is covered here →

Already treated — second opinion
On this page