Choosing a Cataract Lens

Introducing Intraocular Lenses: What are the differences?

In modern cataract surgery, the clouded crystalline lens is removed and replaced by an artificial intraocular lens (IOL). Intraocular lenses represent a highly innovative technology – both in terms of corrective power and the quality of vision provided. Different types of intraocular lenses are available today, enabling good vision at one, two or all three distances:

  • Near: Approx. 40 cm (Reading).
  • Intermediate: Approx. 80 cm (Computer work).
  • Far: Beyond 100 cm (Spatial orientation).
Illustrative demonstration of vision distances covered by modern IOLs.
Different vision distances can be corrected with modern IOLs

Intraocular lenses explained

IOLs can simulate the refractive properties of the natural lens, however they do not have the ability to accommodate. Advanced intraocular lenses are designed to meet additional, individual patient's vision requirements. Depending on the design, the advanced IOLs can offer further benefits, such as improved contrast perception.

Size of intraocular lenses (IOLs) in comparison to an almond.
Actual IOL size compared to an almond

Intraocular lenses are usually made of a soft, synthetic, and biocompatible material. A typical IOL measures approximately between 11 and 13 mm in diameter. The thickness of the lens can vary, depending on its refractive power. The corrective power of the lens is individually calculated and may differ for each eye. An IOL is transparent and neither visible nor perceptible in the eye.

Different Types of Intraocular Lenses

There are different types of intraocular lenses available today. Generally, there is a distinction made between standard and advanced intraocular lenses, also known as premium intraocular lenses.

  • Standard intraocular lenses are the most commonly used implants in cataract treatment. They have one focal point and can improve sight at one distance: far or near. These lenses are called monofocal lenses. For the remaining distances, the patient may still need to use glasses. Advanced versions offer additional advantages on top of treating the cataract. They provide the possibility of being less dependent on glasses for different activities. Advanced products include so-called multifocal, EDoF (Extended Depth of Focus) and aspheric or toric lenses.
  • Multifocal intraocular lenses have two or three focal points and restore vision at more than one distance, giving the patient a chance of being more independent of glasses. Multifocal lenses include trifocal IOLs, representing the most advanced technology. Trifocal options allow the highest level of independence from glasses, enabling patients to see clearly at all three distances without them.
  • EDoF Intraocular lenses also provide a high extent of spectacle independence while inducing less visual side effects at night, compared to multifocal versions.

Added capabilities in advanced IOLs, such as aspheric or toric functions, offer additional advantages for the patients: Toric IOLs allow the correction of pre-existing astigmatism, while aspheric IOLs can improve contrast sensitivity general image quality.

Advanced IOLs allow patients to become less dependent on glasses, and are a good option for patients with active lifestyles and for those wanting more freedom from glasses. Since what they offer are additional benefits for patients, cataract treatment with premium lenses is – depending on in which country you live – not covered by health insurance.

Characteristics of Monofocal IOLs

Clear vision at one distance

This is the most common type of intraocular lens used in cataract surgery. When light enters the eye through a monofocal lens, it is bent to a single focus point on the retina.

Light cannot be focused from both distant and near objects at the same time, so it means that a monofocal lens can correct vision at one distance, providing good visual perception for either near, or far distance.

Most patients choosing this option want to be able to see at a distance, allowing them to perform activities such as driving and watching TV. They usually need to use glasses to help with near vision tasks, such as reading, cooking and working on the computer.

Demonstration of the visual perception with a monofocal IOL in everyday life.
Vision Simulation with a monofocal IOL

Choosing the Right Distance

While most surgeons implant the monofocal option with distant focus to correct far vision, it is also possible to choose a monofocal lens with near correction to enable good vision up close. For all other distances, the patient needs to wear glasses.

The decision about whether distant or near sight should be corrected depends on the patient's lifestyle and visual needs. The decision should be made in agreement with the surgeon after a close consultation with the patient.

A couple enjoying good vision after cataract surgery.
Monofocal IOLs can correct far or near vision.

What You Should Know

Standard types of monofocal IOLs have a spherical optic, which is equally rounded on both sides. It is normally paid for by your health insurance.

However, the natural crystalline lens of the eye has a slightly aspherical (not completely round) shape at the front, and is not equally curved on both sides. This shape enables it to precisely focus light rays entering the eye onto one point on the retina. The result is a clear, crisp image.

Advanced monofocal IOLs are available with an aspherical optic very similar to the original shape of the crystalline lens. The special design of the aspheric versions enable an enhanced image quality.

Additionally, if you have an irregularly shaped cornea, a monofocal lens in a toric version can improve your quality of eyesight considerably. Consult with your ophthalmologist to find out which type of monofocal option is right for you.

Characteristics of EDoF Lenses

Clear vision at intermediate and far distances

EDoF (Extended Depth of Focus) intraocular lenses use an advanced optical technology that allows to increase the range of focus compared to standard monofocal types.

In this way, EDoF solutions enable clear eyesight ranging from far up to intermediate distances, like a computer monitor. For close-up activities such as reading fine print and precision work, patients treated with EDoF lenses may need to wear reading glasses. However, they will experience less visual disturbances at night, which are sometimes caused by bright light sources with multifocal IOLs.

Demonstration of the visual perception with an EDoF IOL in everyday life.
Vision Simulation with an EDoF IOL

How EDoF Lenses Work

EDoF IOLs work by bending the light entering the eye from intermediate and far distances and focusing this light onto a single focal point on your retina. This allows you to focus on objects at these distances simultaneously, providing good intermediate and distance vision through one lens. EDoF IOLs reduce or may even eliminate the need for glasses. Just like prescription glasses, your IOL will also be adjusted to your individual needs to give you the best vision possible.

EDoF IOLs in Everyday Life

Extended Depth of Focus (EDoF) lenses provide sharp vision over a wide range, allowing you to see objects clearly at different distances from far to intermediate: approximately at arm’s length. EDoF IOLs enable you to perform a broad spectrum of activities without glasses, including:
  • Sports
  • Socializing
  • Working on the computer
  • Driving a car
  • Watching TV
  • Cleaning
  • Cooking
  • Shopping 
  • Other typical home and garden tasks

Daily tasks become easier and more enjoyable. Most activities can be fulfilled without needing to wear prescription glasses, however, reading glasses may be necessary for small print.

Advantages of EDoF IOLs

EDoF lenses combine the advantages of both monofocal and multifocal IOLs, providing the perfect balance between increased freedom from glasses and reduced visual side effects typically associated with the multifocal types. Some patients are more, others less sensitive to these light phenomena, which may be experienced as halos or glare around light sources, especially at night.

Patients with EDoF lenses generally enjoy good night vision, which is particularly important for driving after sunset, for example. The undisturbed and reliable visual performance that EDoF lenses provide gives patients a feeling of added comfort and safety.

EDoF IOLs are an ideal fit for individuals wishing to maintain an active lifestyle.

A couple enjoying good intermediate vision after cataract treatment.
With EDoF IOLs you can enjoy good intermediate vision without glasses.

What you should know

EDoF lenses offer a high degree of spectacle independence. However, the achieved vision quality is very individual and may differ from patient to patient.

It also offers a good fit for individuals interested in an IOL that combines greater freedom from glasses with high vision comfort day and night. Consult your doctor to see if an EDoF IOL might also be right for you.

Characteristics of Multifocal Lenses: Trifocal IOLs

Clear vision at all distances

These are the most advanced intraocular lenses (IOLs) available today, providing clear vision for near, intermediate and far distances. They are designed to enable a high degree of independence from glasses for patients leading an active life and wishing to do without visual aids.

Demonstration of the visual perception with a trifocal IOL in everyday life.
Vision Simulation with a trifocal IOL

How Trifocal Lenses Work

Trifocal lenses work by bending the light entering the eye from near, intermediate and far distances, and focusing this light onto a single focal point on your retina. This enables you to focus on objects at different distances simultaneously, providing near, intermediate and distant vision. These modern IOL types reduce, or may eliminate the need for glasses or contact lenses. Just like prescription glasses, your IOL will also be adjusted to your individual needs to give you the best vision possible.

Trifocal Lenses in Daily Life

Unlike monofocal options, trifocal lenses also provide comfortable intermediate vision, which is important for various daily activities, such as computer work.

It allows you to perform a range of activities in everyday life without glasses. This includes daily tasks such as:

  • Reading
  • Cooking, cleaning, ironing
  • Working at the computer
  • Shopping
  • Watching TV
  • Driving
  • Working in the garden
  • Playing sport or doing exercise

Advantages of Trifocal Lenses

The biggest advantage of trifocal IOLs is the possibility to see clearly at all distances without glasses. As a result, you may no longer need to wear glasses when pursuing your daily activities.

Moreover, trifocal solutions allow for the treatment of pre-existing vision disorders, such as myopia or hyperopia. With a toric version of the trifocal lens, pre-existing astigmatism can be corrected as well.

Trifocal intraocular lenses are also effective for treating age-related vision changes such as presbyopia, which affects nearly everyone after the age of 40. When you treat your cataract with a trifocal IOL you can take care of your presbyopia at the same time.

In short, trifocal IOLs offer a high chance to become independent from glasses or contact lenses.

A dancing couple enjoying their spectacle-free vision at all distances after cataract surgery.
With trifocal IOLs you may no longer need glasses

What you should know

Like with all innovative technologies, there are also a few things to consider when choosing a trifocal lens.
If you suffer from eye diseases, such as glaucoma, diabetic retinopathy, diabetic macular oedema, or macular degeneration, you may not be a suitable candidate for trifocal lenses. These diseases, even in early stages, may be incompatible with premium intraocular lenses. If you suffer from one of these diseases, you can discuss alternative options with your ophthalmologist.
Light phenomena
One side effect connected with multifocal solutions is a higher degree of visual disturbances and light phenomena (dysphotopsia), which are caused by the lens focusing light from multiple distances. These are normally perceived as
  • Glare in certain low lighting situations.
  • Halos around light sources at night.

Most people with multifocal lenses find these phenomena only mildly disturbing and get used to them over time. However, there is also a small group of patients who do not adapt well or are very bothered by the side effects that may occur. Simulations of potential halo and glare perceived after the surgery help the patient prepare for the possible side effects.
Ask your doctor about the light disturbances during your consultation to check if you are the right candidate for a trifocal IOL.

Decreased contrast sensitivity
Another consequence of the multifocality might be a slightly less perfect image quality. This is due to the lens splitting light from different distances on the retina. Therefore, patients have to compromise a little on the image quality to gain the multifocal effect.

Aspheric and Toric IOL Functions

Additional advantages of advanced cataract treatment options

In addition to the advantages offered by multifocal and EDoF IOLs, advanced solutions offer some more functions for a better vision. For instance, aspheric lenses correct certain light phenomena and improve contrast, providing an optimized image quality.

Toric intraocular lenses enable the treatment of astigmatism, a common vision disorder affecting roughly one third of the global population and causing distorted vision.

Both IOL types: the aspheric and toric IOLs have special characteristics to enable clear, crisp images. These additional functions are not always covered by the national health care system. Please check with your doctor if an aspheric and/or toric IOL is recommended in your case and discuss the potential extra costs of the lens.

Characteristics of Aspheric Lenses

Standard types of monofocal IOLs have a spherical optic, which is equally curved on both sides. However, the natural crystalline lens of the eye has a slightly aspherical (not completely round) shape at the front. This enables it to precisely focus the light rays entering the eye on one point of the retina.
Advanced monofocal IOLs are available with an aspherical optic just like the shape of the natural lens, which allows you to have a vision as close as possible to natural vision.

How Aspheric Lenses Correct Vision

The special, not uniformly curved, design of the aspheric IOLs enables the correction of spherical aberrations.

What is a spherical aberration?

A spherical aberration is a visual defect that occurs when light rays passing into the eye are not precisely focused at one single focal point. When we are young, the cornea and lens of the eye work together to focus the entering light rays at exactly one point on the retina, optimizing image contrast.

As we grow older, that interaction deteriorates, causing reduced vision quality. This means:

  • Vision gets blurry.
  • Contrast perception is decreased, leading to difficulty seeing in low-light conditions.

With aspheric IOLs, light rays entering the eye are once again sharply focused at a single point on the retina. The result is improved contrast sensitivity and an enhanced image quality, especially during activities such as driving at night or reading in dim lighting conditions.

If you are already suffering from spherical aberration or you want to prevent this visual change, an aspherical IOL may be a suitable option for you. Discuss this option with your ophthalmologist.

Demonstration of the visual perception with a spheric and an aspheric IOL.
Vision simulation with a spheric (left) and an aspheric IOL (right).

Characteristics of Toric Lenses

Correcting irregularly shaped corneas for clear vision

Visual acuity is an important factor for patients. The possibility of correcting astigmatism using toric intraocular lenses during a cataract procedure is a great option for patients suffering from both conditions. Astigmatism is a refractive error like near- or farsightedness. This error is usually the result of an irregularly shaped cornea, which leads to light not being properly focused on the retina. It causes objects at different distances to appear skewed or distorted.

How Toric Lenses Correct Astigmatism

A toric lens is shaped in a certain way. The shape of toric lenses is significantly unlike other types of corrective lenses, as they feature two different curvatures.
The shape of toric lenses creates various refractive powers on the vertical and horizontal axis. The combination helps to focus all incoming light properly onto your retina to reduce or eliminate astigmatism.
How toric lenses are implanted in the eye
If you decide to have a toric IOL, the surgical procedure is slightly different to normal cataract surgery. It must be implanted in a very specific position in the eye, meaning:
  • Depending on the type of lens, just prior to cataract surgery, temporary markings may need to be placed on your cornea that identify the location of the most curved meridian.
  • During surgery, the toric IOL is implanted in your eye.
  • Once implanted, each toric lens is rotated until the markings are aligned with the markings on your cornea.

If you have astigmatism and would like to correct it during cataract surgery, consult your doctor to discuss the implantation of toric IOLs.

Demonstration of the vision affected by astigmatism and corrected with a toric IOL.
Vision simulation with astigmatism (left) and with a toric IOL (right).

Vision Simulation Tool Experience how different types of intraocular lenses may correct your visual disorders!
Your ZEISS IOL information Have you been implanted with an intraocular lens from ZEISS and/or are you looking for product information on ZEISS IOLs?

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