How it works
A monofocal lens has the same power across its whole surface. It focuses all the light on a single plane of sharp vision. Nothing is split and nothing is lost, which is why it gives the best image quality of all the lens families.
The sharp distance is chosen before the operation. Most often, distance vision is given priority: driving, recognising a face, watching television. Reading glasses, often of low power, take care of near vision.
What it offers
- The best quality of vision available at the chosen distance, with contrast intact.
- No halos or glare caused by the lens itself, which matters for driving at night.
- Full cover by the Assurance Maladie: no supplement for you to pay.
- No ocular contraindication: it can still be implanted with a fragile macula, advanced glaucoma or retinopathy.
What it requires
You will need glasses for anything outside the chosen distance. If distance vision was given priority, that means reading, your phone and close-up screen work.
This is not a failure of the surgery. It is the trade-off accepted from the outset. Many patients live with it very well, because they were already wearing reading glasses.
The “monofocal plus” variant
A recent development extends the zone of sharp vision slightly towards intermediate distance (a screen, a car dashboard, prices on a shop shelf), without the optical drawbacks of lenses with several focal points. The loss of contrast is minimal and halos are rare.
Fine print still needs glasses. The supplement is not covered by the Assurance Maladie, but it is lower than for EDOF and multifocal lenses. It often offers the best balance between what you gain and what it costs in image quality.
Monovision
One eye can be set for distance and the other for a closer distance. The brain learns to favour the right eye for whatever it is looking at. This reduces dependence on glasses without the optical drawbacks of a multifocal lens, but it does not suit everyone. You need to tolerate the difference between your two eyes, and this can be tested beforehand with contact lenses.
Who it is the right choice for
Patients whose retina or optic nerve is fragile, which rules out premium lenses. People who drive a lot at night. Those who are happy to wear reading glasses, and there are more of them than you might think. And those who would rather have the security of a predictable result than the promise of a glasses-free life that is never guaranteed.
One point of substance: choosing a monofocal lens is not settling for less because of cost. It is often the most reasonable decision, and I recommend it more often than not.
If you have astigmatism
Significant corneal astigmatism leaves vision blurred at all distances, whatever the lens. There is a toric version of the monofocal lens that corrects it. See the page on the toric lens.
Possible complications
First, those of any cataract surgery, which I describe on the cataract page. Two relate to the lens itself:
- Posterior capsule opacification: the membrane that holds the lens can become cloudy over time. This is called secondary cataract, and it is treated with a YAG laser.
- Displacement of the lens: this is rare.
In the first few days, mild dry eye and a feeling of something in the eye are usual. The complications are the same for the monofocal plus variant.
The monofocal lens, with and without toric correction
A monofocal lens has only one focal point, most often set for distance vision. The light is not split: all of its energy serves that distance, which gives the best contrast and the best night vision of all the lens families. It is the reference lens.
A single focal point, set for distance vision. Glasses are still needed for intermediate distance and reading.
The same principle, with correction of astigmatism. Its axis must be aligned precisely.
Sharp vision without glasses Variable comfort Glasses needed Toric axis marks
The golden halo shows the marks engraved on the optic, which must be lined up with the steepest meridian of the cornea. The choice is made case by case, depending on the cornea, the retina, visual habits and tolerance of halos.
The monofocal plus lens
It looks the same as a monofocal lens, but its shape is slightly modified to stretch the zone of sharp vision towards intermediate distance. Contrast stays close to that of a monofocal, without the light-splitting of multifocal lenses.
Distance vision is preserved, and intermediate distance (a screen, a car dashboard) becomes more comfortable. Reading still needs glasses.
The intermediate comfort of the monofocal plus, combined with correction of astigmatism.
Sharp vision without glasses Variable comfort Glasses needed Toric axis marks
The gain at intermediate distance is real but modest, and varies from one patient to another, hence the pale green on the bar. The choice is made case by case, depending on the cornea, the retina, visual habits and tolerance of halos.
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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