Which lens implant to choose, and how far will you see clearly?

Once the natural lens has been removed, it has to be replaced. The implant stays in place for good: it cannot be changed like a pair of glasses. It is the only truly personalised decision in the whole operation.

The principle, in one sentence

A young natural lens changes shape to focus at every distance. No lens implant can do this. Every implant is a compromise: it chooses where to put sharp vision, and what it is willing to give up to get it.

The four families

The monofocal lens places sharp vision at a single distance, most often far away. Distance vision is excellent, with maximum contrast. You need glasses to read. It is the only lens implant fully covered by French national health insurance (Assurance Maladie), and also the safest in terms of quality of vision.

The monofocal plus lens extends the zone of sharp vision slightly towards intermediate distance: the car dashboard, the computer screen, arm's length. Fine print still needs glasses.

The extended depth of focus lens, known as EDOF, stretches the range of sharp vision continuously from distance to intermediate. It is a compromise between comfort and contrast.

The multifocal lens divides the light between several focal points, so you can see at distance, at intermediate range and up close. It is the one that most often frees you from glasses, and the one that asks the most of your eye.

The price of independence from glasses

A lens implant that divides the light between several distances sends, by design, less light to each focal point. The result is a loss of contrast and, frequently, halos around lights at night.

These effects fade over time: the brain learns to ignore them, a process called neuroadaptation. But it takes several weeks, sometimes several months, and it is never guaranteed. A patient who drives a lot at night should know this beforehand, not discover it afterwards.

When some lens implants are ruled out

This is the most important point in this article, and the one least often explained.

AMD (age-related macular degeneration) rules out the multifocal lens, and in most cases the EDOF lens too: a weakened macula cannot tolerate the extra loss of contrast. Advanced glaucoma leads to the same conclusion, for the same reason applied to the optic nerve. Diabetic retinopathy, even mild, points towards a monofocal lens.

Marked dry eye, an irregular cornea or previous refractive surgery also make the lens calculation harder and can affect the quality of the result.

In other words, a premium lens implant is not an extra you buy. It is an option your eye either allows or does not.

And astigmatism?

Each of these families comes in a toric version, which corrects corneal astigmatism. Without this correction, significant astigmatism leaves vision blurred at every distance, whatever lens implant is chosen.

How the decision is made

The pre-operative assessment measures the length of your eye, the curvature and thickness of your cornea, and the condition of the macula and optic nerve. These measurements first rule out what is not possible. Only then do we look at your habits: do you read a lot, drive at night, work on a screen, would you accept glasses for reading?

A patient who is happy to wear reading glasses has nothing to gain from a multifocal lens. That is not settling for less: it is often the best choice.

Sources Société Française d'Ophtalmologie (French Society of Ophthalmology), information leaflet on cataract surgery (in French).
Haute Autorité de Santé (French National Authority for Health), multifocal intraocular lenses, health technology assessment (in French).
Rampat R., Gatinel D., Multifocal and extended depth-of-focus intraocular lenses, Ophthalmology.