What “extended depth of focus” means
The name comes from photography, where the same idea is called depth of field. A camera lens with a shallow depth of field brings only one precise plane into focus; a lens with a large depth of field keeps acceptable sharpness over a range of distances.
The EDOF lens applies this principle. Instead of splitting light into two or three distinct focal points, it stretches a single focal point into an elongated zone. The result is a continuous transition, with no jump in sharpness between distance and intermediate.
What you will see
- At distance: clear, with a quality close to that of a monofocal lens.
- At intermediate distance: a screen, a car dashboard, prices on a shop shelf are clear as well. This is the main gain.
- Up close, for fine print: glasses are still needed in most cases. Some patients can read medium-sized print without them, others cannot.
Of the lens families, this is the one that best covers office work and driving, and the weakest with a book in small print.
What it costs in image quality
Spreading light out always has a price. An EDOF lens causes a loss of contrast that is smaller than with a multifocal lens, but real. Night-time light effects do occur, more as a diffuse halo or streaks than as the concentric rings of a multifocal.
These effects fade over time, through neuroadaptation. This takes anywhere from a few weeks to a few months, and it is never guaranteed.
A combination worth knowing about
An EDOF lens can be placed in one eye and a monofocal lens set for near vision in the other, or two EDOF lenses can be set at slightly offset distances. This widens the overall range of clear vision while limiting the optical drawbacks. It is discussed case by case, depending on your dominant eye and your habits.
When it is ruled out
Like the multifocal lens, an EDOF lens is not advised if you have AMD (age-related macular degeneration), advanced glaucoma or diabetic retinopathy: the loss of contrast it brings adds to the loss already caused by the disease.
Marked dry eye, an irregular cornea or previous refractive surgery also make the calculation harder and affect the quality of the result.
Who it is for
An active patient who works on a screen, drives in daylight and accepts glasses for long periods of reading. Someone who wants to rely less on glasses without accepting the marked halos of a multifocal lens. The extra charge for this lens is not covered by French national health insurance (Assurance Maladie).
Possible complications
First, there are those of any cataract surgery, which I describe on the cataract page. Three 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.
- Halos around lights: they stay faint with an EDOF lens, much less marked than with a multifocal lens.
The EDOF lens, with and without toric correction
A central zone changes the way light is focused and stretches the depth of focus, instead of creating several distinct focal points. Clear vision extends from distance to intermediate, with fewer halos than a multifocal lens. Fine print often still needs glasses.
The zone of clear vision is stretched, from distance to intermediate. Fine print often still needs glasses.
Extended depth of focus, combined with correction of astigmatism.
Clear vision without glasses Variable comfort Glasses needed Toric axis marks
The central ring represents the optical zone responsible for this stretching; it cannot be seen with the naked eye on the actual lens. The choice is made case by case: cornea, retina, visual habits, 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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