In a cataract, the clear lens inside the eye clouds over the years, vision becomes blurry, lower in contrast and more sensitive to light. The good news: the clouded lens can be replaced with a clear artificial lens. The real question is then less whether than which, and lens selection and calculation are exactly where my work focuses.
The lens sits behind the pupil and focuses light sharply onto the retina. With age it loses its clarity and takes on a tint, much as hair turns grey over the years. It is a natural process, not a failing: almost everyone develops a cataract sooner or later. Usually both eyes are affected, often at different times. (Background: the lens is made of fine proteins; with age they rearrange and cloud, similar to how clear egg white turns white and opaque when heated.)
Vision changes as if you were looking through an increasingly fogged, milky window pane: contours soften, colours fade, and light sources, headlights, the sun, dazzle more and develop halos. Frequent changes of glasses that no longer help are another typical sign.
Glasses only shift the focal point, they can readjust a blurred image but cannot wipe a cloudy pane clear again. As long as the clouding sits within the lens itself, the image stays dull, no matter how good the glasses are. Only replacing the lens restores clarity.
During surgery the clouded lens is removed and replaced with a clear artificial lens (intraocular lens, IOL) that stays permanently in the eye. The procedure is one of the most common and best-studied of all and is usually performed on an outpatient basis under local anaesthesia, one eye at a time. As with any procedure, we weigh benefit and effort individually and discuss the course and possible risks calmly beforehand.
Because the artificial lens stays for life, choosing it is the most important decision. At its core lies a physical trade-off: every lens works with the same amount of incoming light. It can either concentrate that light onto one distance, where the image is then especially sharp and high in contrast, or split it across several distances, so you see at more distances without glasses, but each distance receives a smaller share. Much like the difference between single-vision and progressive glasses, only fixed inside the eye.
Many assume a lens for distance simply adds to what they already see, such as sharp near vision. In reality your own lens currently provides that sharpness. If it is removed and replaced with a monofocal distance lens, you gain distance but give up the familiar, unaided near vision and will then need reading glasses there, even if you can read without glasses today. A monofocal lens focuses at exactly one distance; which one that should be we decide together beforehand, to match your daily life.
Strength: highest contrast and few optical side effects, sharp at one main distance (usually distance). Trade-off: for the other distances, usually reading, you need glasses. Reliable and well tolerated.
Strength: a stretched zone of sharpness from distance into the intermediate range (screen, dashboard), with fewer halos than multifocal lenses. Trade-off: for reading small print a light pair of glasses is often still needed. A middle path.
Strength: seeing without glasses in many everyday situations, near and far. Trade-off: the split light can create halos and glare at night and slightly reduce contrast; not every eye is suitable, and a healthy retina and a regular cornea are prerequisites. Honest counselling about these trade-offs matters to me, they are not a defect but physics.
If your eye has astigmatism, it is shaped more like a rugby ball than a football. A toric lens is ground to match and compensates for this curvature. It can be combined with monofocal, EDOF or multifocal lenses and must be aligned precisely inside the eye.
There is no single “best” lens, there is the one that fits you. Which that is follows from your eyes, your daily life (work, driving, hobbies) and your willingness to accept optical trade-offs. That is exactly what we discuss, unhurried.
As important as the lens type is its power, and that must be measured and calculated individually for each eye, like a tailored suit cut to exact measurements rather than off the peg. Because the lens is implanted once and stays, the accuracy of this calculation co-determines your later vision. This is one of my research focuses: I have co-published on formulas for calculating lens power, among them the Castrop formula, and am an appointed member of the IOL Power Club, an international specialist circle on the science of lens calculation. So the selection and calculation of your lens flows into the consultation first-hand, not from a brochure.
Calculation becomes especially demanding in eyes that depart from the norm: after refractive laser correction (LASIK, PRK or SMILE), with Fuchs' endothelial dystrophy, with corneal scars or with keratoconus. Here standard formulas often give inaccurate values because the cornea no longer matches the usual assumptions. These difficult cases, and how corneal power can be determined more precisely in them, are the subject of my research (Ophthalmic Physiol Opt, 2025; Z Med Phys, 2025).
→ Research & publications on lens power calculation
For cataract surgery too, a femtosecond laser can take over individual steps, such as incisions or opening the lens capsule (femtosecond laser-assisted cataract surgery, FLACS).
What does the laser do, and what is the thinking behind it? It prepares two steps that are otherwise done by hand. First, the circular opening of the lens capsule, comparable to a tailor who marks and pre-cuts an exactly round piece. The thinking behind it: the position of this opening influences how the new lens later sits, which matters especially with toric and premium lenses. Second, the laser divides the clouded lens into fine segments beforehand, like a grid that pre-cuts a solid block into puzzle pieces, so that less ultrasound is needed to remove it. I then carry out the actual operation myself; the laser does not replace it, but prepares individual precision steps.
Honestly put: for routine cataract surgery, comparative studies show no advantage in the visual result over the established manual technique, at higher cost, an equally good result can be achieved by hand. But "not proven" does not mean "no benefit": potential advantages for the long-term position and centration of the lens, which matters especially with premium IOLs, can barely be demonstrated in studies today, because lens tilt and centration can only be measured reliably over years with a few, rarely available devices. Such long-term data therefore simply do not (yet) exist.
What can be observed: the laser creates a very evenly round, centred capsule opening. And in special situations, such as weakened lens support (zonulolysis) or a sensitive corneal endothelium (Fuchs dystrophy), it can be practical, because less manual work is needed on the lens itself. Whether it is useful in your case we discuss individually, without any automatism.
Special case keratoconus. With a deformed cornea, lens choice and calculation are considerably more demanding. → Cataract in keratoconus
Not yet presbyopic and simply want to be rid of glasses? Then the ICL may be worth a look, an additional lens that preserves your own. → About the ICL
Residual refractive error after lens surgery? A small deviation can be fine-tuned afterwards, with a corneal laser or an add-on lens. → Fine-tuning after lens surgery
Whether and when to operate and which lens makes sense depends on your eyes and your daily life. In the consultation we measure the eye, interpret the findings honestly and discuss the lens options with their pros and cons, without pushing toward a premium solution.
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