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.
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.
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.
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.
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
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
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
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.
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.
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.
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.
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 (Pentacam or equivalent) is required to map these irregularities, quantify the aberrations and guide the choice of implant.
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.
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