How it works, and what follows
A multifocal lens has several concentric optical zones, which create two or three focal points at the same time. Your brain constantly selects the sharp image and ignores the others.
The consequence is a matter of physics, and it cannot be avoided: the light entering the eye is divided between these focal points. Each image therefore receives less energy than with a monofocal lens. Every advantage and every drawback of this family of lenses comes from this.
What you gain
A degree of independence from glasses that no other option provides. In published series, a large majority of patients with multifocal lenses manage without glasses or contact lenses in everyday life, including for reading. It makes a real difference from one day to the next.
What you accept
- A loss of contrast, especially noticeable in low light.
- Halos and rings of light around light sources at night. This is the most common complaint, and it mainly affects night driving.
- A period of neuroadaptation lasting from several weeks to several months, during which these effects are more troublesome than they will be afterwards.
- A greater need for precision in calculating the lens: a power error that would go unnoticed with a monofocal lens becomes a real nuisance here.
The question I always ask
Do you drive at night, and how often? A patient who drives at night several times a week (for work, on poorly lit roads) is not a good candidate, even if every eye criterion is met. The discomfort is not unusual. It is expected, and it may never go away completely.
When it is ruled out
This is not negotiable, whatever the patient asks for.
- AMD (age-related macular degeneration), even at an early stage: the macula cannot tolerate any further loss of contrast.
- Glaucoma with visual field loss: the same reasoning, applied to the optic nerve.
- Diabetic retinopathy, even mild, or a history of macular oedema.
- An irregular cornea, keratoconus, or severe dry eye that is not under control.
Over the age of sixty-five, one in two candidates for cataract surgery has at least one of these conditions. That is why, despite its reputation, the multifocal lens is implanted in only a minority of cases.
Possible complications
First, there are those of any cataract surgery, which I describe on the cataract page. Three are specific to the lens itself:
- Posterior capsule opacification: the membrane that holds the lens in place can become cloudy over time. This is known as secondary cataract, and it is treated with a YAG laser.
- Displacement of the lens: this is rare.
- Halos and reduced contrast: this is the trade-off. Because the light energy is shared, contrast is lower and halos around lights are common, especially in the first few months.
If the result does not suit you
Exchanging the lens is technically possible, but it is a second operation inside the eye, with its own risks. It is done only very rarely. Prevention comes before surgery: complete information, and a deliberate decision not to go ahead when the conditions are not met.
The multifocal lens, with and without toric correction
Diffractive rings divide the light between several focal points: distance, intermediate and near. It is the only family of lenses that covers all three distances without glasses. The trade-off is that, because the light energy is shared, contrast is lower and halos around lights are common, especially in the first few months.
Several focal points share the light: distance, intermediate and near. The trade-off: halos around lights are common in the first few months.
All distances, plus correction of astigmatism. Of all lenses, this is the one that needs the most precise alignment.
Clear vision without glasses Variable comfort Glasses needed Toric axis marks
This lens requires a regular cornea, a healthy retina and a patient who understands the compromise: it is not suitable for everyone. The choice is made case by case, looking at the cornea, the retina, your visual habits and how well you tolerate 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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