Choosing an IOL: monofocal vs multifocal vs EDOF, a pre-op primer

Somewhere between "you have a cataract" and the day of surgery, your surgeon's office will ask you a question that catches many people off guard: which lens implant do you want? You went in expecting a medical decision and instead you are handed something that feels like a consumer choice, often with a price difference attached. And unlike glasses, you do not get to try it for a week and swap it — the intraocular lens (IOL) that goes in during surgery is, for practical purposes, permanent.

The short version: the core trade-off is between image quality at one distance and freedom from glasses across many. A monofocal lens gives one crisp focal distance with the best contrast, but you will usually still wear glasses for part of your range. Multifocal and extended-depth-of-focus (EDOF) lenses spread focus across more distances so you need glasses less — at the cost of some contrast sensitivity and more night-time halos. Neither is universally 'better'; the right pick depends on your eyes, your priorities, and how you feel about glasses. Here is the plain-English version to bring into that conversation.

What an IOL actually does

Your natural lens sits behind the pupil and does two jobs: it bends incoming light to help focus it on the retina, and — when you are young — it flexes to shift focus between far and near. Cataract surgery removes that lens once it clouds and replaces it with a clear artificial one. The catch is that a standard IOL cannot flex. It is a fixed optic, so it focuses light at a distance (or distances) chosen in advance, and that is where the different lens types diverge.

The choice is really a choice about how to handle presbyopia — the age-related loss of the eye's ability to shift focus — because a fixed lens cannot do it for you the way a young natural lens once did.

Monofocal: one sharp distance, best contrast

A monofocal lens has a single focal point. You and your surgeon choose where it sits — nearly always distance, so you can drive and watch television without glasses, and use reading glasses for close work. (Some people choose "monovision," setting one eye for distance and the other for near.)

The great strength of a monofocal lens is that it devotes all the light entering your eye to one focus. That means the sharpest, highest-contrast image the optics can deliver, and generally the fewest night-time visual artifacts. The trade-off is equally simple: you will need glasses for the distances the lens is not set to. For many people — especially anyone who already wore glasses happily for decades — that is a perfectly comfortable deal, and it is why the monofocal remains the default and the benchmark against which the others are judged.

Multifocal: several distances, at a cost

A multifocal IOL is designed to give usable vision at more than one distance without glasses. Most work by splitting incoming light among two or more focal points (for example, one for distance and one for near, with trifocals adding intermediate). Your brain learns to attend to whichever image is in focus and suppress the others.

The appeal is obvious — more tasks without reaching for readers. But splitting light has consequences. Because no single focal point gets all the light, and because the concentric rings in many multifocal optics can scatter it, multifocal lenses tend to lower contrast sensitivity and increase glare and halos around lights at night. How large and how lasting the contrast effect is depends on the lens design: one early study of a refractive multifocal found contrast sensitivity was reduced relative to a monofocal in the first months after surgery but had largely caught up with the monofocal group by around six months (Montés-Micó & Alió, 2003).¹ The glare-and-halo side of the trade is the more consistent finding. A Cochrane systematic review pooling 20 randomized trials found that people with multifocal lenses were less dependent on glasses but markedly more likely to report glare — and, especially, halos — than those with monofocal lenses (de Silva and colleagues, 2016).² That is the bargain in one sentence: fewer glasses, more glare and halos, and less light devoted to any single focus.

EDOF: a stretched focus, a middle path

Extended-depth-of-focus (EDOF) lenses are a newer category that tries to soften the trade-off. Instead of creating two or three separate focal points, an EDOF lens elongates a single focal point into a continuous zone, aiming for a smoother range of clear vision — typically strong distance and intermediate (dashboards, computer screens), with near vision that is improved but often still assisted by light readers.

The idea is to capture much of the range benefit while producing fewer of the rings and starbursts that split-light multifocals can cause. In practice, EDOF lenses still sit between monofocal and multifocal on the contrast trade-off. A multi-centre randomized trial comparing two EDOF lenses against a monofocal found that the monofocal delivered better contrast sensitivity, while the EDOF lenses gave better intermediate and near vision and a higher rate of spectacle independence (Reinhard and colleagues, 2021).³ So EDOF is best understood not as a free lunch but as a deliberately positioned compromise: more range than a monofocal, more contrast than a full multifocal, and a good fit for people who want to reduce (not necessarily eliminate) glasses without a heavy night-vision penalty.

Note: a contrast sensitivity test is a screening signal of overall visual function. It cannot tell you which IOL to choose, cannot measure a lens before it is implanted, and does not replace your surgeon's assessment of your eyes and goals. It is only useful here as a way to understand and, later, track the kind of function these lenses trade against.

How to think about the choice

The lens types are tools for different priorities, so start with your own life rather than the brochure.

• How do you feel about glasses? If you have worn them contentedly for years, a monofocal lens plus readers may be the least-fuss, highest-quality option. If being free of glasses matters a lot to you, a multifocal or EDOF lens buys that — at a contrast cost you should go in expecting.
• How much do you drive at night? Night driving is the scenario where halos and reduced contrast bite hardest. Heavy night drivers often prefer a monofocal. Our pieces on halos and starbursts after cataract surgery and night driving after cataract surgery walk through what those artifacts feel like and how they relate to lens design.
• What else is going on in your eyes? This is where your surgeon's judgment is decisive. Because multifocal and EDOF lenses reduce contrast, they are often avoided in eyes with macular disease, glaucoma, corneal irregularity, or significant dry eye — conditions that already tax contrast. In those cases a monofocal is frequently recommended to preserve as much contrast as possible.
• What are your intermediate tasks? Lots of computer and dashboard time favors an EDOF or trifocal design's intermediate strength; a monofocal set for distance leaves that range to glasses.

There is no lens that is simply best. There is a lens that best matches your priorities and your eyes, and finding it is a conversation, not a purchase.

One more practical note: the range-of-focus lenses (multifocal and, to a lesser degree, EDOF) tend to demand a period of neuroadaptation, during which the brain learns to make sense of the multiple or stretched focal points and to suppress halos. Early after surgery, night-time artifacts and a slightly "busy" visual quality are common and usually diminish over weeks to months — a normal part of the process rather than a sign the wrong lens was chosen. Knowing that up front prevents unnecessary alarm in the first weeks, and it is one reason surgeons often ask about your patience for an adjustment period when discussing these lenses.

What to do next

You cannot test-drive an IOL, but you can walk in prepared. Our guides to what to expect after cataract surgery and to glare and the bright-light problem fill in the neighboring details, and the questions in our what to ask your eye doctor piece translate directly to a pre-op visit.

Bring your real priorities in concrete terms: how much you drive at night, how you feel about readers, what your day's near and intermediate tasks look like, and whether you have any other eye conditions. Those specifics are what turn "monofocal, multifocal, or EDOF" from a brochure into a decision.

If you want a functional reference point, you can take a free contrast sensitivity test before surgery and again once your eyes have settled afterward, on the same device under similar lighting. It will not choose a lens for you, but it can make the contrast trade-off these lenses involve concrete rather than abstract — a companion to your surgeon's guidance, not a substitute for it.