IOL description and movie | Huntereyesurgeons

Read below how Dr Peter Davies describe the types of intra-ocular lenses to his patients.

Best quality image,
More need for glasses

Less need for glasses, Less quality image

Intraocular Lens Choices at Cataract Surgery

Dr Peter Davies

1. Introduction

When you have cataract surgery or lens replacement surgery, your natural lens is removed and replaced with an artificial intraocular lens (IOL). There are many types of IOLs available, but they can be grouped into three main categories:

Single focus (monofocal) lenses
Extended depth of focus (EDOF) lenses
Multifocal lenses

Choosing the right lens is one of the most important decisions you and your surgeon will make.

2. Single Focus (Monofocal) Lenses

Focus all light into a single focal point.
Provide the sharpest image quality and the best vision in dim light (e.g., night driving, working in low light).
Preferred by professions requiring precise detail: airline pilots, doctors, lawyers, architects, artists, and musicians.
Often the safest choice if you have other eye conditions such as dry eye, floaters, macular degeneration, or glaucoma.

3. Multifocal Lenses

Designed to focus light at two or more distances (near, intermediate, distance).
Achieved by modifying the central part of the lens, known as the optic.
This modification is proprietary — meaning it is a trade secret. We do not know the exact design details for each company.
Common methods include:
- Adding refractive rings
- Adding diffractive rings
- Altering the spherical aberration of the optic
The benefit is greater spectacle independence. The trade-off is reduced image clarity (especially in dim light) and a higher chance of side effects such as glare, halos, or reduced contrast sensitivity.

4. Extended Depth of Focus (EDOF) Lenses

Positioned between monofocal and multifocal designs in terms of performance.
Extend the range of clear focus without splitting light as aggressively as multifocals.
Examples include Eyhance, RayOne EMV, Zoe, Puresee, and Vivity.
Offer a middle ground: some increased near vision with fewer side effects than multifocals, but less image sharpness than monofocals.

5. The Trade-Off Triangle

The choice of lens involves balancing three factors:

Image quality (best with monofocals)
Range of vision without glasses (best with multifocals)
Risk of side effects (lowest with monofocals, highest with multifocals)

Visual Chart – Quality vs Near Vision vs Side Effects:

A blue triangle represents image quality: highest at the monofocal end, lowest at the multifocal end.
A green triangle represents near vision: lowest at the monofocal end, highest at the multifocal end.
Side effects increase as you move from left (monofocal) to right (multifocal).

6. Important Surgical Considerations

If you have other eye disease, a monofocal is usually safest.
Sometimes we remove an EDOF or multifocal lens and replace it with a monofocal if side effects are unacceptable.
We never remove a monofocal lens to replace it with a multifocal.

7. Summary

Monofocal: Best image quality, safest choice, but glasses likely for reading.
EDOF: Middle ground, some reading without glasses, some loss of sharpness.
Multifocal: Maximum spectacle independence, but highest risk of reduced night vision quality and other visual side effects.

Final Advice:
Discuss your work, lifestyle, and night vision needs with your surgeon to decide which lens is right for you. This is a personalised choice—there is no “one-size-fits-all” answer.

Read on for a more verbose description of this important question, or click here to move onto the remainder of the information - the process of cataract surgery.

Which intra-ocular lens should you chose?

There are many brands of intra-ocular lens (IOL), but three basic types: mono-focal (or single focus) lenses, extended depth of single focus lenses (EDOF) and multifocal lenses. And each lens type can have a “toric” correction to reduce the astigmatism in your cornea.

Monofocal lenses usually require reading glasses afterward, while multifocal and EDOF lenses may reduce or eliminate the need for glasses both for reading and distance.

Toric lenses correct astigmatism, which can also reduce glasses dependence.

Ask yourself this question. Are you a “best quality vision person”, or an “I hate glasses person”? These are the two extremes which reflect the two ends of the IOL range, from single focus through to multifocal.

!. Single focus IOL

With single-focus lenses, all the light is focussed on one optical plane, or distance.

A single focus lens looks like the lenses you have seen before. It has smooth curved surfaces that gives you the highest quality vision, because it is only doing one job – focusing light in one plane, like a camera lens. However, it cannot shift or change its’ focus. Where the eye is focused is where it stays focused.

These give the best quality image because all the light is focussed on one plane. We use these lenses for most patients, because most patients want best quality. These lenses give the eye "best-quality vision" as they have the least side effects. They have a greater requirement for spectacles, especially for near work. These are best for eyes with any other pathology such as macula degeneration or dry eye. As most patients with cataract are elderly and have other eye disease, we prefer these lenses, because if there is reduced vision afterwards, we can sharpen the vision with glasses and we know that residual reduced vision is not due to the lens inside the eye.

Usually with single focus lenses, we use “Blended vision”, where we focus the first eye for slight near work, and most patients find that they have reasonable distance and intermediate vision. We then use the refractive result from the first eye we do to fine tune the focus in the second eye, which is focussed for distance. So you are more likely to need glasses

For most patients, we choose a single-focus lens that is focussed for distance. In this case you will need reading glasses. However, we can choose a single-focus lens focussed for near, and occasionally do this on the patient’s request.

2. Multifocal lenses

At the other end of the spectrum are multifocal lenses. These lenses are designed for patients who do not want to wear glasses.

These lenses look like lighthouse lenses, with concentric rings in them. The rings focus the light in different focal planes. They aim to remove the need for glasses for both distance and near viewing. They take 100% of the light and focus some for distance viewing, some for near viewing, and scatter the remaining light. This can cause halos around lights at night, although in time patients learn to ignore these effects. Contrast sensitivity (ability to distinguish shades of grey and colour) is also slightly reduced. Your Doctor can use this lens for you. This lens is a good option for patients who never want to wear glasses, or are physically disabled and cannot wear glasses. We would avoid using this lens in patients of a “meticulous” personality, such as Doctors, Lawyers, Architects, Accountants, Artists, Musicians. We cannot use this lens in Pilots.

Multifocal lenses aim to reduce the need for glasses, but at the cost of reducing quality of vision, because the lens is scattering (and not focussing) some of the light. The manufacturers manipulate the centre of the lens, to create different zones of focus.

They can cause rings around lights, and can cause glare and haze, and reduced quality vision. This is worse in dim light conditions. Floaters are more obvious with multifocal IOL’s, and patients are more likely to need vitrectomy to remove them.

When we use multifocal lenses, we sometimes need to exchange them for single focus lenses, if patients are unhappy with the quality of vision.

Before you have cataract, you can try multi-focal contact lenses to get some sense of what they can do and what they cannot do. I find that, in bright light conditions, multifocal contact lenses can work well, albeit with a ghost image around objects, and slightly reduced vision. In dim light however, I still need reading glasses and the quality drops off, with rings around headlights and increased glare and haze. I never wear multifocal contact lenses when I am performing high quality vision tasks such as macula surgery and flying an aeroplane – for these tasks I always wear progressive spectacles.

What the manufacturers actually do to the lens is unknown, as this is “proprietary” information, meaning “secret company information” subject to commercial patents. So each lens design is slightly different from another. This makes it difficult to compare different lens types, because companies do not pay for independent clinical comparison trials. At Newcastle Eye Hospital Foundation, Dr Peter Davies studies the huge amounts of data that we gather, but it is still very difficult to distinguish between IOL’s.

There is a new generation of multifocal lens coming called the Galaxy. The manufacturer claims that the lens was designed with the assistance of artificial intelligence, and that this lens has less side effects than traditional multifocal lenses. We need to wait and see for independent data to confirm these claims.

3. Extended Depth of Single Focus lenses.

Between these two types, are "extended depth of single focus lenses". They were introduced around 2018. These lenses aim to extend the focal range, whilst reducing the side effects of multifocal lenses. They have some of the benefits of a multifocal lens, with less side effects. They reduce the quality of the image, but not as much as a multifocal lens does, and they do not have the same near focus. They are increasingly popular as they are a compromise between the two extremes of single focus and multifocal lenses.

But in general, these are lenses that increase the depth of focus, or range of focus, but do so at the cost of reducing quality of vision. These lenses sit between the single focus and the multifocal lenses.

Dr Davies compared 6 versions of EDOF, and we found that the RayOne EMV lens was preferred by our group of patients. This is a very popular lens in Europe.

This is an important conversation that every patient should have with their surgeon.

Ask yourself these questions

1. Are you a "best quality vision" person OR an "I hate glasses" person?

2. Are you very physically active?

3. Do you drive at night, or do activities in dim light conditions?

4. Do you mind wearing glasses when you need them for certain activities?

5. Do you understand that the focus of your eyes will drift and change throughout life, whatever focus the surgery initially achieves for you?

Some patients do not like the visual side effects of multifocals and EDOF’s, and occasionally these lens needs to be removed. Removing a lens needs to occur within 4 weeks from the original surgery. We sometimes need to exchange EDOF’s and MFIOL’s for single focus lenses. BUT WE NEVER REMOVE A SINGLE FOCUS LENS AND REPLACE IT WITH A MULTIFOCAL LENS.

THERE IS NO PERFECT INTRAOCULAR LENS.

GLASSES GIVE BEST QUALITY VISION REGARDLESS OF WHAT LENS YOU CHOSE.

ARE YOU HAPPY WEARING GLASSES? DO YOU WANT BEST QUALITY VISION? IF SO, CHOSE A MONOFOCAL LENS. YOUR SURGEON WILL BE HAPPY BECAUSE THEY WILL HAVE LESS PROBLEMS.

DO YOU DISLIKE GLASSES? ARE YOU ARE HAPPY TO ACCEPT THE RISK OF MULTIFOCAL LENSES? THEN CHOSE MULTIFOCALS.

NOT SURE? THEN one of the EDOF's ARE A POPULAR CHOICE. You can pick one along a range of EDOF and side effects as per the diagram above.

Some surgeons refer to Premium lenses. We don’t as we believe this is misleading. All the lenses we use are “premium”. When doctors use the term premium lenses, they are referring typically to extended depth of focus or multifocal lenses.